Studying different etching methods for several types of ...

Republic of Iraq Ministry of Higher Education And Scientific Research Al-Mustansiriyah University College of Science

Studying different etching methods for several types of S.S.N.T.ds. A Thesis Submitted to the College of Science Al – Mustansiriyah University in Partial Fulfillment of the Requirements for the Degree of Master of Science in Physics

By

Layth Abdulhakeem Jebur (B. Sc. 2012) Supervised by

Dr. Nada F. Khadhim Assistant professor Physics Department 2016 A.D

1437 A.H

Abstract This research includes study different techniques chemical etching for nuclear track detector, and try to estimate the appropriate time for etching alpha particle and fission fragments latent tracks originated in two solid state nuclear track detectors (CR-39 and CN-85) using chemical etching induced with three different techniques; water bath, microwave and ultrasound, In order to recognize the effects of these techniques and shortening the etching time. It was found, the optimum etching time for CR-39 detector irradiated with alpha particles etched in water bath, microwave and ultrasound would be (60-150 minute), (20-30 minute) and (60-120 minute) respectively. And the optimum etching time for CN-85 detector irradiated with alpha particles etched in water bath, microwave and ultrasound would be (30-35 minute) (10- 15 minute) and (20-35 minute) respectively. And the optimum etching time for CR-39 detector in fission fragments etched in water bath, microwave and ultrasound would be (4560 minute) (45- 60 minute) and (20-30 minute) respectively. Calculate parameters track etching: the bulk etch rate (VB), the track etch rate (VT), the track etch rate ratio evaluates (V), critical angle (θc), etching efficiency (η). (First) calculate the bulk etch rate (VB) at the three using devices (water bath, microwave, ultrasound) as follows: CR-39 detector when irradiated with alpha particles the result was respectively (1.15, 4.00, 1.22) and CN-85 detector when irradiated with alpha particles the result was respectively (5.23, 12.42, 6.45) and when CR-39 detect fission fragments in soil samples the result was respectively (2.05, 3.41, 2.10).

I

(Second) calculate the track etch rate (VT) at the three using devices (water bath, microwave, ultrasound) as follows: CR-39 detector when irradiated with alpha particles the result was respectively (2.62, 9.5, 2.87) and CN-85 detector when irradiated with alpha particles the result was respectively (7.13, 23.36, 9.75) and when CR-39 detect fission fragments in soil samples the result was respectively (4.60, 7.73, 4.60). (Third) calculate the track etch rate ratio evaluates (V) at the three using devices (water bath, microwave, ultrasound) as follows: CR-39 detector when irradiated with alpha particles the result was respectively (2.278, 2.375, 2.352) and CN-85 detector when irradiated with alpha particles the result was respectively (1.36, 1.88, 1.51) and when CR-39 detect fission fragments in soil samples the result was respectively (2.24, 2.26, 2.19). (Fourth) calculate critical angle (θC) at the three using devices (water bath, microwave, ultrasound) as follows: CR-39 detector when irradiated with alpha particles the result was respectively (26.03, 24.9, 25.15) and CN-85 detector when irradiated with alpha particles the result was respectively (47.18, 32.11, 41.41) and when CR-39 detect fission fragments in soil samples the result was respectively (26.46, 26.17, 27.16). (Fifth) calculate etching efficiency (η) at the three using devices (water bath, microwave, ultrasound) as follows: CR-39 detector when irradiated with alpha particles the result was respectively (0.561, 0.58, 0.575) and CN-85 detector when irradiated with alpha particles the result was respectively (0.267, 0.469, 0.339) and when CR-39 detect fission fragments in soil samples the result was respectively (0.550,0.558,0.540).

II

Supervision certification I certify that this thesis entitled “Studying different etching methods for several types of S.S.N.T.ds.” was prepared by (Layth Abdulhakeem Jebur) under my supervision at Department of Physics, College of Science, Al-Mustansiriya University, as a partial fulfillment of the requirements for the degree of Master of Science in Physics.

Signature: Name: Dr. Nada F. Khadhim Scientific Position: Professor Address: Department of Physics College of Science, AL-Mustansiriya University. Date: / / 2015

In view of the available recommendation, I forward this thesis for debate by the Examination Committee.

Signature: Name: Dr. Ali Abid D. Al-Zuky Scientific Position: Professor Address: Head of Physics Department, Collage of Science, AlMustansiriya University. Date: / /2015

Acknowledgments First of all, praise is to our Almighty Allah gracious for enabling me to finish what I have started and for helping me to present this work. A great thank and appreciation goes to my supervisor Dr. Nada F. Khadhim for her constant support and for suggesting the subject of my thesis and her cooperation, her scientific, academic advices and for giving me her invaluable time during the time of my research. Without her help, this work would not be possible. My gratitude goes to the dean of collage of science and head of the department of physics for their help. Thanks and appreciation to my Dr. Ali Abdulwahab, Dr. Basem. I would like to thank my family for their great and continuous supports, patience, and encouragement. Thanks and appreciation to all my friends, and in particular to the brother Ahmed M.Abid Alasady.

List of contents List of figures VI List of Tables IX No. Chapter One " General Introduction" Page (1-1) Introduction 1 (1-2) Types of Radiation 2 (1-2-1) Ionizing Radiation 2 (1-2-2) Non-Ionizing Radiation 2 (1-3) Sources of Ionizing radiation 2 (1-3-1) Natural Background 3 (1-3-1-1) Cosmic Rays 3 (1-3-1-2) Terrestrial Radiation 4 (1-3-2) Artificial (man-made) sources of ionizing radiation 7 (1-4) The Radioactive decay Low 7 (1-5) Heavy charged particles 8 (1-5-1) Alpha particle 8 (1-5-2) Nuclear fission 9 (1-6) The Radiation Detection 10 (1-7) Previous Studies 12 (1-8) Aim of the study 15 Chapter Two " Theoretical Background" (2-1) Introduction 16 (2-2) Formation of a latent track 17 (2-3) Characteristics of nuclear latent track 18 (2-3) Types of Solid state nuclear track detectors (SSNTDs) 19 (2-4) Detection thresholds of track detectors 20 (2-5) The etching techniques for solid state nuclear track 22 detectors (SSNTDs) (2-5-1) Chemical etching (CE) 22 (2-5-2) Electrochemical etching (ECE) (2-5-3) Microwave-induced chemical etching 24 (2-5-4) Ultrasonic chemical etching (UCE) 25 (2-5-5) Plasma etching (dry etching) 26 (2-6) Parameters track etching 26 (2-6-1) Bulk etch rate (VB) 27 (2-6-1-1) Thickness measurement method 27 (2-6-1-2) Track diameter measurement method 27 (2-6-1-3) Mass Change method 28 (2-6-1-4) Measurement method the track's diameter-length (Le-D) 28 (2-6-2) Track etch rate (VT) 29 (2-6-3) Etching rate ratio (V) 30 III

(2-6-4) (2-6-5) (2-7) (2-8) (2-9) (2-10) (2-11) (2-11-2) (2-11-2) (3-1) (3-2) (3-2-1) (3-3) (3-3-1) (3-4) (3-4-1) (3-4-2) (3-4-3) (3-4-3-1) (3-4-3-2) (3-5) (3-5-1) (3-6) (3-6-1) (3-7) (3-8) (3-8-1) (3-8-1-1) (3-8-2) (3-8-2-1) (3-8-2-1-1) (3-8-2-2) (3-8-2-2-1) (3-8-2-3) (3-8-2-3-1) (3-9) (3-10) (3-10-1) (3-10-2) (3-10-3 (3-11)

Critical angle of etching (θC) Etching efficiency (η) Track Geometry CR-39 detector CN-85 Track detector Applications of solid state nuclear track detectors The Americium Americium-241 (Alpha source) 241 Am-Be neutron source Chapter Three " Experimental Technique" Introduction Collection and preparation of soil Samples Test sieve Samples sites and coding Electric oven Pressing the soil samples Connecting material (starch) Hydraulic Press Solid state nuclear track detectors CR-39 detector CN-85 detector Irradiation of the soil samples with neutrons Neutron source Irradiation of the track detectors with alpha Alpha source (Americium-241) Dose calculation Chemical etching Preparation of the Etchant solution Hot plate Stirrer Chemical etching techniques Chemical etching with water bath Water bath device Chemical etching with ultrasound waves Ultrasonic cleaner device Chemical etching with microwaves Laboratory microwave device Cleaning and drying the detectors Viewing the detectors Track density measurement Optical microscope Digital Camera Sensitive balance IV

30 31 32 34 36 36 37 37 39 40 40 40 41 42 43 43 44 44 44 45 45 46 46 47 48 48 48 49 50 50 50 50 51 52 52 53 53 53 54 54 55

(4-1) (4-2) (4-3) (4-3-1) (4-3-1-a) (4-3-1-d) (4-3-1-1) (4-3-1-2) (4-3-1-3) (4-3-2) (4-3-2-1) (4-3-2-2) (4-3-2-2) (4-4) (4-4-1) (4-4-2) (4-4-3) (4-5) (4-6) (4-6-1) (4-6-1-1) (4-6-1-2) (4-6-1-3) (4-6-2) (4-7) (4-8)

Chapter Four " Result and discussion" Introduction Time estimation of developing latent track by chemical etching Time estimation of alpha latent tracks Time estimation of alpha latent tracks in CR-39 detectors CR-39 detector in touch with alpha source CR-39 detector at a separation distance from alpha source Chemically etching with water bath device Chemically etching with microwave device Chemically etching with ultrasound device Time estimation of alpha latent tracks in CN-85 detectors Chemically etching with water bath device Chemically etching with microwave device Chemically etching with microwave device Etching time estimation for CR-39 detector irradiated with neutron emitted from (241Am-Be) Chemical etching with water bath Chemical etching microwave device Chemical etching with ultrasound device Calculations of chemical etching parameters Discussion Etching time Chemically etching of CR-39 detector irradiated with alpha Chemically etching of CN-85 detector irradiated with alpha Chemically etching of CR-39 detector irradiated with fission fragments Etching parameters of the track Conclusions Future Works References

V

56 56 57 57 57 58 59 60 62 64 64 65 67 69 69 71 72 74 84 84 84 86 88 91 92 93

No.

List of Figures

Page

(1-1) (2-1) (2-2) (2-3)

Natural radiation sources and man-made Formation of a latent track Shows the damage from radiation (a) crystals (b) polymers Critical angle of etching θC (a) θ> C (e.g. Normal incidence), (b)  < C and, (c)  =C (i.e. Critical angle) Three phases in the track development. (I) Is the initial detector surface, O and E are the entrance and end points of the particle path R, (1) Conical track; (2 and 3) the track wall is partially conical and partially spherical; (4) the track is fully spherical Three phases in the track development. (I) Are the initial detector surface, O and E are the entrance and end points of the particle path,(1) Conical Phase (X1) (Y1, t1),(2) Transition Phase (X2) (Y2, t2), (3) Spherical Phase (X3) (Y3, t3) The chemical form of CR-39 plastic Decay Scheme of 241Am Test sieve Samples collection sites on Al-Mustansiriyah University map Electric oven used to dry soil samples The hydraulic press and cast Fission Track occur in sandwich of soil sample and two slices of solid state nuclear track detector The design used to irradiate the detectors with the alpha particles emitted from americium source Americium-241 source Hot plate strirer Water bath device Ultrasounic cleaner device using in our research Laboratory microwave device Optical microscope Camera installation user Sensitive balance View of enlarged tracks originated in CR-39 detector after exposed in touch with (Am-241) alpha source Views of CR-39 detector etched chemically at (30, 90, 150, 240) minutes with water bath Views of CR-39 detector etched chemically at (10, 20, 30, 40) minutes with microwave device Views of CR-39 detector etched chemically at (30, 90, 150, 240) minutes with ultrasound device

3 18 20 31

(2-4)

(2-5)

(2-6) (2-7) (3-1) (3-2) (3-3) (3-4) (3-5) (3-6) (3-7) (3-8) (3-9) (3-10) (3-11) (3-12) (3-13) (3-14) (4-1) (4-2) (4-3) (4-4)

VI

33

34

35 38 41 42 43 44 46 47 47 49 50 51 52 54 55 55 58 60 61 63

(4-5) Four views of CN-85 detector etched chemically at (15, 25, 35, 45) minutes with water bath (4-6) Views of CN-85 detector etched chemically at (5, 10, 15, 20 minute) with microwave device (4-7) Four views of CN-85 detector etched chemically at (15, 25, 35, 45 minute) with ultrasound (4-8) Four views of CR-39 detector etched chemically at (15, 45, 60, 90) minutes with water bath (4-9) Four views of CN-39 detector etched chemically at (10, 20, 30, 40) minutes with microwave (4-10) Four views of CR-39 detector etched chemically at (15, 45, 60, 90) minutes with ultrasound (4-11) Slope between track diameter and etching time for CR-39 detector etched with water bath (4-12) Slope between track diameter and etching time for CR-39 detector etched with laboratory microwave device (4-13) Slope between track diameter and etching time for CR-39 detector etched with ultrasound (4-14) Slope between track diameter and etching time for CN-85 detector etched with water bath (4-15) Slope between track diameter and etching time for CN-85 detector etched with microwave (4-16) Slope between track diameter and etching time for CN-85 detector etched with ultrasound (4-17) Slope between track diameter and etching time for CR-39 detector etched with water bath (4-18) Slope between track diameter and etching time for CR-39 detector etched with microwave (4-19) Slope between track diameter and etching time for CR-39 detector etched with ultrasound (4-20) Alpha track density against etching time for (CR-39) detector etched with water bath and irradiated at different doses (4-21) Alpha track density against etching time for (CR-39) detector etched with microwave and irradiated at different doses (4-22) Alpha track density against etching time for (CR-39) detector etched with ultrasound and irradiated at different doses (4-23) Alpha track density against etching time for (CN-85) detector etched with water bath and irradiated at different Doses (4-24) Alpha track density against etching time for (CN-85) detector etched with microwave and irradiated at different doses (4-25) Alpha track density against etching time for (CN-85) detector VII

65 67 68 70 72 73 78 78 79 79 80 80 81 81 82 85 85 86 87

88 88

etched with ultrasound and irradiated at different doses (4-26) Track density of fission fragments against etching time for (CR-39) detector etched with water bath (4-27) Track density of fission fragments against etching time for (CR-39) detector etched with microwave (4-28) Fig (4-28) track density of fission fragments against etching time for (CR-39) detector etched ultrasound

VIII

89 90 90

No.

List of Tables

(1-1) The natural decay series for 238U, 235U and 232Th (2-1) Some nuclear track detectors, and its specifications (2-2) Some etching conditions for organic and inorganic nuclear track detectors (3-1) The samples codes and their gathering locations (3-2) Alpha doses calculated according to times of irradiation (4-1) Track densities in CR-39 detector at different doses and various etching times when using water bath device (4-2) Track densities in CR-39 track detector at the different doses and various etching times using microwave device (4-3) Track densities in CR-39 track detector at the different doses and various etching times using ultrasound device (4-4) Track densities in CN-85 track detector at the different doses and various etching times using water bath device (4-5) Track densities in CN-85 track detector against different doses and various etching times using microwave device (4-6) Track densities in CN-85 track detector against different doses and various etching times using ultrasound device (4-7) Track densities in CR-39 track detector at different doses and etching times using water bath device (4-8) Track densities in CR-39 track detector at different doses and etching times using microwave device (4-9) Track densities in CR-39 track detector at different doses and etching times using microwave device (4-10) The etching time, average diameter and bulk etch rate for CR-39 detector etched with water bath (4-11) The etching time, average diameter and bulk etch rate for CR-39 detector etched with microwave (4-12) The etching time, average diameter and bulk etch rate for CR-39 detector etched with ultrasound (4-13) The etching time, average diameter and bulk etch rate for CN-85 detector etched with water bath (4-14) The etching time, average diameter and bulk etch rate for CN-85 detector etched with microwave (4-15) The etching time, average diameter and bulk etch rate for CN-85 detector etched with ultrasound (4-16) The etching time, average diameter and bulk etch rate for fission fragments in CR-39 detector etched with water bath (4-17) The etching time, average diameter and bulk etch rate for fission fragments in CR-39 detector etched with microwave IX

Page 6 21 23 41 48 59 62 63 65 66 68 70 71 73 74 75 75 75 76 76 76 77

(4-18) The etching time, average diameter and bulk etch rate for fission fragments in CR-39 detector etched with ultrasound (4-19) Etching parameters of CR-39 detector irradiated with alpha (4-20) Etching parameters of CN-85 detector irradiated with alpha (4-21) Etching parameters of CR-39 detector irradiated with fission fragments in soil samples

X

77 83 83 83

Chapter One

General Introduction

Chapter One General Introduction

(1-1) Introduction Radiation is energy in the form of waves or streams of particles. There are many kinds of radiation around us. Atomic energy, nuclear power and radioactivity, but the radiation has many other forms. Sound and visible light are familiar forms of radiation; other types include ultraviolet radiation, infrared radiation, and radio and television signals [1]. Radiation is naturally present in our environment and has been since the birth of this planet. Consequently, life has evolved in an environment which has significant levels of ionizing radiation. Radiation comes from outer space (cosmic), the ground (terrestrial), and even from within our own bodies. It is present in the air we breathe, the food we eat, the water we drink, and in the construction materials used to build our homes. Certain foods such as bananas and nuts naturally contain higher levels of radiation than other foods [2-3]. Brick and stone homes have higher natural radiation levels than homes made of other building materials such as wood and contains higher levels of natural radiation than most homes [2-3]. In physics, radiation is a process in which energetic particles or energetic waves travel through a medium or space. Two types of radiation are commonly differentiated in the way they interact with normal chemical matter [4]

1

Chapter One


(1-2) Types of Radiation (1-2-1) Ionizing Radiation Ionizing radiation is capable of takeoffs electrons out of their orbits around atoms, and giving the atom a positive charge. Electrically charged molecules and atoms are called ions [1]. Materials are ionization in two ways (directly or indirectly) [5-6]: 1-Directly ionizing radiation: electrons, protons, particles and heavy ions, i.e. individual particles with adequate kinetic energy can directly disrupt the atomic structure of the absorbing medium through which they pass producing chemical and biological damage to molecules. 2-Indirectly ionizing radiation: photons (x-rays and δ-rays), neutrons, they do not produce chemical and biological damage themselves, but produce secondary electrons (charged particles) after energy absorption in the material. (1-2-2) Non-Ionizing Radiation The energy of non-ionizing radiation is low, do not produce charged ions when passing through matter, the electromagnetic radiation has only sufficient energy to change the rotational, vibrational or electronic valence configurations of molecules and atoms [3]. Non-Ionizing radiation includes: electromagnetic radiation these include radio waves, microwaves, infrared, visible light, and sometimes ultraviolet [4].

(1-3) Sources of Ionizing radiation Sources

of

ionizing

radiation

include

natural

radiation

(background) and radioactive materials (man-made). As shown in figure 2

Chapter One


(1) natural background (radon 54.5%, cosmic 7.9 %, terrestrial 7.9%, internal 10.9%) and man-made (medical x-ray 10.9%, nuclear medicine 4%, consumer products 3%), other ˂ 0.9% [7].

Fig. (1-1) Natural radiation sources and man-made [7]. (1-3-1) Natural Background Many radioisotopes are naturally occurring, and originated during the formation of the solar system and through the interaction of cosmic rays with molecules in the atmosphere, as well as some radioisotopes (such as uranium and thorium) in our environment [3]. Background radiation is the ionizing radiation constantly present in the natural environment. There are three sources of the public exposure to natural radiation: cosmic radiation, terrestrial radiation, radioactivity in the body by (inhalation and ingestion) [1]. (1-3-1-1) Cosmic Rays Cosmic rays are a type of radiation that comes from outer space consisting primarily of charged particles (87 % protons, 11 % alpha 3

Chapter One


particles and 1 % the nuclei of atomic number between (26-4), and 1% electrons very high energy). The earth‘s atmosphere absorbs some of this radiation and in the process produces secondary radiation of reduced intensity consisting of subatomic particles such as muons (µ -) and electrons [8-9]. The atmosphere acts as a shield and reduces very considerably the amount of cosmic ray reaching the earth's surface. Radionuclides arises from the interaction of fast neutrons in cosmic radiation with nitrogen in the upper atmosphere to form

14

C as follows:

14

N (n, p)

14

C, where

14

C

has a half-life of (5568) years and diffuses to the lower atmosphere where it may become incorporated into living matter [10]. (1-3-1-2) Terrestrial Radiation Terrestrial radiation comes from radionuclides that occur naturally in rock and soil such as

238

U, 235U, 232Th series and their decay products,

this three series emit alpha particles mainly addition to beta and gamma rays, so it was found that the mass number of each element of the series is a multiple of four (mass number of rays alpha) [11-12]. The emission of alpha and beta particles, accompanied by a change in the number of nucleons (protons and neutrons) in the nucleus and the instability of the nucleus in terms of energy, in order to reach the nucleus of stability emits of gamma rays [13]. The Uranium 238 U Series P

It is the head of the uranium decay series, of which U-234 is a member, it is available as a percentage (99.27%) of uranium isotopes, and half-life 4500 million years. Its typical concentration in soil is (1pCi/g) [14-15]. 4

Chapter One


This series begins with the element uranium-238 (238U) which is parent nucleus, ends at stable isotope lead-206 (206pd) and accompanied by the emission of alpha or beta at decay and also radiation gamma with most of the elements [14-15]. The number of nucleons were be calculated from the law (4n + 2), and this means that the number of nucleons, is divisible by (4) and the rest is (2) [16]. The decay series is shown in table (1-1). The actinium 235 U Series P

U-235 is the head of the actinium decay series with abound of (0.71%), and half-life 710 million years, its typical concentrations in soil are (1pCi/g) [17]. This series begins with uranium-235, which suffers many of the decay and ending with the stable isotope lead-207 (207Pb) [14-15], The number of nucleons were be calculated from the law (4n + 3), and this means that the number of nucleons is divisible by (4) and the rest is (3) [16]. The decay series is shown in table (1-1). The thorium 232Th Series Pure thorium is a silvery white metal it is presenting the second radioisotope coming after uranium. Its atomic mass is 92, its mass number 232, its melting point 1750 C˚, its boiling point 4700 C˚, its density is (11.72gm/cm3) [15-16], its exist in very little concentration in the nature, natural thorium consists almost entirely of

232

Th , 1.35x10-8 %

of 228Th and extremely small amounts 234Th, 230Th, 231Th and 227Th [15]. The series starts with thorium isotope -232 (232Th) and ends with a stable isotope of lead-208 (208Pb), and many suffer from decay accompanied by the emission of alpha particles or beta, and gamma with 5

Chapter One


most of the elements [14-15], The number of nucleons were be calculated from the law (4n) [16]. The decay series is shown in table (1-1). Table (1-1) the natural decay series for 238U, 235U and 232Th [17]. Natural

238

U decay series

Natural

235

U decay series

Natural

232

Th decay series

Nuclide Half-life Decay mode Nuclide Half-life Decay mode Nuclide Half-life Decay mode 238

4.5E+09y

α

235

24.10 d

β

231

1.17 min

β

231

2.5E+05y

α

227

7.5E+04y

α

227Th

Ra

1.6E+03y

α

223

Rn

3.85 d

α

223

3.1 min

α

219

At

1.5 s

α

219

Pb

27 min

β

215

Bi

19.9 min

β

215

Po

1.6E–04 s

α

215

Tl

1.30 min

β

211

Pb

22.6 y

β

211

Bi

5.01 d

β

211

Po

138.4 d

α

207

Hg

8.2 min

β

207

Tl

4.20 min

β

Pb

(Stable)

(Stable)

U

234Th 234

Pa

234

U

230Th 226 222

218

Po

218

214

214 214

210 210

210 210 206

206 206

U

7.0E+08y

α

232

Th

1.06 d

β

228

3.3E+04y

α

228

Pa

Ac 2.2E+01y

α (1.4%)

Th 1.4E+10y Ra

5.75 y

β

Ac

6.13 h

β

1.913 y

α

Ra

3.66 d

α

Rn

55.6 s

α

228Th

β (98.6%)

18.7 d

α

224

Fr

21.8 min

β

220

Ra

11.43 d

α

216

At

56 s

α

212

Rn

3.96 s

α

212

7.6 min

β

212

α

208 208

Bi

Po 1.8E–03 s At

1.0E–07 s

α

Pb

36.1 min

β

Po

25.2 s

α

2.14 min

α

Tl

4.77 min

β

Pb

(Stable)

(Stable)

Bi

6

α

Po 1.5E–02 s Pb Bi

10.64 h 1.01 h

Po 3.0E–07 s Tl 3.053 min

Pb

(Stable)

α β α (36%) β (64%) α β (Stable)

Chapter One


(1-3-2) Artificial (man-made) sources of ionizing radiation Radionuclides are produced industrially, shelling stable nuclides by charged particles or neutrons for nuclear reaction process, where the radionuclides utilized in various medical and industrial fields produce and other [19]. Plenty of sources of man-made radiation exist in medical examinations man made radiation is associated with x-rays and diagnostic or therapeutic materials, radioisotopes are produced as a by-product of the operation of nuclear reactors, and by radioisotope generators like cyclotrons. Many man-made radioisotopes are used in the fields of nuclear medicine, biochemistry, the manufacturing industry and agriculture. In addition the earth‘s atmosphere has been contaminated with the fallout from atmospheric testing of nuclear weapons [20]. Some isotopes: cobalt (60CO), cesium (137Cs), americium (241Am) [19].

(1-4) The Radioactive decay Low Decay is automatic particle emission from the nucleus unstable, decay is subject to the law of exponential [21-22]. 𝑁 = 𝑁𝑜 𝑒 −𝜆𝑡 …………………. (1-1) Where: (No): Represents the number of nuclides parent nucleus at the time (t = 0). (N): Represents the number of nuclides parent nucleus, remaining at the time (t). (λ): Constant decay (time rate of decay). (t): Decay time (decay time from the beginning until the time of measurement). 7

Chapter One


We get a constant decay (λ) of the following formula, which contains a half-life (t1/2) [23-24]. 𝑙𝑛2

=𝑡

1/2

=

0.693 𝑡1/2

…………….……… (1-2)

The activity A(t) of a radioactive substance containing a large number N(t) of radioactive atoms represents the total number of decays per unit time, as in the equation (1-3). 𝐴 = 𝜆𝑁 = 𝜆𝑁𝑜 𝑒 −𝜆𝑡 = 𝐴𝑜 𝑒 −𝜆𝑡 ……….. (1-3) The decay constant (λ) and mean-life (T) are related through the following equation [24]. 1

𝑡1/2



𝑙𝑛2

𝑇= =

= 1.44𝑡1/2 ………………. (1-4)

The mean life (T), can also be defined as the time required for the number of radioactive atoms or activity to fall to (1/e = 0.368) of its initial value (No) or initial activity (Ao).

(1-5) Heavy charged particles A charged particle is called ‘heavy’, if its rest mass is large compared to the rest mass of the electron. Such as mesons, protons, αparticles, and of course fission fragments are all heavy charged particles. Electrons and positrons are ‘light’ particles [22]. (1-5-1) Alpha particle The alpha particle consists of (2) neutrons and (2) protons, is essentially the same as the nucleus of a helium atom. Because it has no electrons, the alpha particle has a charge of (+2). This positive charge causes the alpha particle to strip electrons from the orbits of atoms in its vicinity [4]. 8

Chapter One


As the alpha particle passes through the material, it removes electrons from the orbits of atoms it passes near. And the energy of the alpha particle is reduced by each reaction. In the end the particle will expend [4]. The most well-known source of alpha particles is an alpha decay of heavy atoms. When an atom emits an alpha particle in alpha decay, the atom's mass number decreases by four due to the loss of the four nucleons in the alpha particle. The atomic number of the atom goes down by exactly two, as a result of the loss of two protons the atom becomes a new element. Examples are when uranium becomes thorium, or radium becomes radon gas, due to alpha decay [25]. The short range of absorption, alphas are not, in general, dangerous to life unless the source is ingested or inhaled, in which case they become extremely dangerous. Because of this high mass and strong absorption, if alpha-emitting radionuclides do enter the body (upon being inhaled, ingested, or injected), alpha radiation is the most destructive form of ionizing radiation. The most energetic alpha particles are stopped by a few centimetres of air or a sheet of paper [26]. (1-5-2) Nuclear fission In the fission reaction the incident neutron enters the heavy target nucleus, forming a compound nucleus that is excited to such a high energy level (Energy excitation > Energy critical) that the nucleus "splits" (fissions) into two large fragments plus some neutrons. An example of a fission reaction is shown below, large amount of energy is released in the form of radiation and fragment kinetic energy [27-22]. 1 0𝑛

236 ∗ + 235 92𝑢 → ( 92𝑢 ) →

140 55𝑐𝑠

9

93 + 37 𝑅𝑏 + 3( 10𝑛)…….(1-5)

Chapter One


Nuclear fission produces asymmetric masses with high probability. The mass distribution of fission fragments from

235

U is thus bimodal in

distribution. All fission fragments are radioactive and most decay through several steps to stable daughters. The decay of the collective fissionproduct activity following the fission of a number of atoms at t = 0 is given by the equation A ≅ 10-16 t-1.2 curies /fission Where (t) is in days, this expression can be used for estimating residual fission product activity between about 10 s and 1000 h [27].

(1-6) The Radiation Detection 1-Gaseous detectors Gas detectors, consist from cylinder-shaped chamber a gas-filled (air, CO2, or argon), containing two electrodes (anode and cathode), connected to a power supply (battery), which provides the needed voltage for detector operation. The electric circuit may include a series of resistors to expand the scale of readings. The readout may be analog or digital. The scales may be calibrated to give readings in c/min, mR/h, or μSv/h [28]. 2- The scintillation detectors The scintillation detectors. Consists of scintillation matter and a light-pipe and the light-reflector, and the photon photomultiplier tube. It is used for the detection of all ionizing radiation. The radiation or nuclear particles fall on a fluorescent screen of (zinc sulfide) then on the scintillator material, the emission of scintillation 10

Chapter One


light travels through photomultiplier tube to photocathode, and the reflector restores light to anode to producing an electrical pulse. The scintillations material types, organic crystals such as anthracene, stilbene, and terphenyl, and liquid solutions containing scintillators as solutes and plastics with scintillating, the crystal (NaI) the most widely used in scintillation detectors [29]. 3-Semiconductor detectors The semiconductor detectors, formation of an electron-hole pair in a semiconductor such as silicon or germanium requires an energy of only about (3eV), so, when these crystals are used as solid-state ionization chambers, they provide large signals for very little energy deposition in the medium. Solid-state devices can therefore be particularly useful for applications at low energies [30]. 4-Track detectors Track detectors comes in the second chapter 5-Neutron Detectors Methods for neutron detection and measurement are based largely on of secondary interaction for determining the neutron. As for thermal neutrons using one of material, lithium (Li) or boron (B), where thermal neutrons interact with material with the emission of alpha particles high-energy. As for fast neutrons, it is preferably detected using apostate proton in dispersion (interaction) fast neutrons with hydrogen. Equipped with the crystal in the form of a mixture of granules zinc sulphide (ZnS) and the wax because it contains hydrogen [31]. 11

Chapter One


(1-7) Previous Studies 1- Studies used different methods of etching: In 2009, S. P. Tripathy et al., study the use of microwave-induced chemical etching (MCE) technique is introduced, for the first time to etch the SPTDs with much less (about on the tenth) time as compared to the traditional etching methods (CE and /or ECE). The alpha tracks started appearing just after 10min of etching and were fully developed after 25 min, which usually takes several hours of CE and ECE techniques. The tracks were observed to be developed clearly with well defined, smooth and sharp edges thereby improving the measurements using an image analyser. The MCE technique is found to be promising, simple, faster and convenient [32]. In 2014, H. Saeed Al-Nia’emi, Study the effect of 40 kHz ultrasound (US) in chemical etching of alpha particle tracks in CR-39 solid state nuclear track detector. Alpha particle irradiations (using 1 µCi 241

Am source). He observed the effect of ultrasound on the chemical

etching process, and particularly the etching on the surface (VB) [33]. In 2015, Anaam Yassen, study the chemical etching of fission fragment in CR 39 and Lexan track detector use water bath and microwave device separately. It was found that the optimum etching time for CR-39 detector is (30 min and 8 min) when etching with water bath and microwave respectively, and is was (60) and (5) for Lexan in water bath and microwave respectively [34]. 2- Studies which have been calculated (VB, VT): In 1996, Nada Fadhil Tawfik, study the properties of organic nuclear track detector CR 39 and CN 85 at different etching conditions, 12

Chapter One


and calculate of parameters track etching and find the best values for the bulk etch rate (VB) and the track etch rate (VT) produced by fission fragments and α-particles, determination of uranium concentration in soil samples from different Iraqi, used as a source of nuclear fission fragments by source (Am-Be) [35]. In 2000, Dunia Fadhil. Study measure the radioactivity emitted by radon from building materials, in addition to the effect of etching time on a detector weight (w), track diameter (D) for CR-39 and CN-85, and calculated their (VB, VT, θc, η) [36]. In 2000, M.R. El-Aasser et., study the bulk etch rate (VB) the track diameter and alpha range in a CR-39 track detector exposed to U.V. and different energies of alpha particles emitted from 241Am source [37]. In 2003, Ali Abdul-Abbas, study the effect of the electric field on the sensitivity of the plastic nuclear track detector, by calculating the bulk etching rate (VB) nuclear track detectors CR-39. I've found that the etching rate of speed decreases with increasing electric field values leading to improved sensitivity of the detector [38]. In 2004, D. Nikezic, study the formation and growth of tracks in nuclear track materials and calculate the bulk etch rate (VB). The dependences of (VB) on different parameters such as the preparation procedures, etching conditions, irradiation before etching, etc. are examined. Review of existing methods for determination of the bulk etch rate and track etch rate (VT) is also given [39]. 3- Study of radioactive sources in the soil: In 1986, Ellis Australia, study determine the concentrations of uranium in samples of marine sediment using the nuclear impact detector 13

Chapter One


(CR-39) study showed that uranium concentrations ranging from (14.149.9ppm) [40]. In 1999, Ajaj F. A., study estimated the uranium content in three rock samples in Mekkah (Saudi Arabia) using CR-39 detectors. Uranium concentration is about 1.9±0.7 ppm [41]. In (2005), Nesha’at R. Al-Ataby, study the radioactivity environmental soil Tuwaitha area and some surrounding units using a detector nuclear impact (CR-39), the concentrations of uranium at depth (cm 5-15) ranging from (0.065-3.875 ppm) [42]. In (2006), Mustafa A. Al-Baidhani, determine concentration of uranium in the soil to areas of Baghdad, Karbala, Basra, using the nuclear impact detector (CR-39), and was the highest concentration (2.73 ppm) in Aeltagy - the Baghdad area, and the lowest concentration (1.57 ppm) in the region industrialized Karbala [43]. In 2007, M. F. Zaki and Y. H. EL-Shaer, Egypt. Study the response of CR-39 (for two types) to alpha particles from two sources, energy 5 MeV and

241

238

Pu with

Am with energy 5.4 MeV. The methods of etching

and counting are investigated, along with the achievable linearity, efficiency and reproducibility. The sensitivity to lower activity and energy resolution are studied [44]. In 2009, Ali Q.R., estimated uranium concentration in soil samples taken from different sites on the national highway between Baghdad and Ramadi using SSNTDs. Uranium concentrations were varying from 1.03 ppm to 7.1 ppm [45]. In 2011, Tawfiq et al., "Measured the uranium concentrations in the soil of Thi-Qar, Basra and Baghdad Governorates using CR-39 14

Chapter One


detectors". The uranium concentrations were 16.38ppm, 16.1 ppm and 0.78 ppm in Thi-Qar, Basra and Baghdad, respectively [46].

(1-8) Aim of the study 1. Estimate the optimum etching time of CR-39 and CN-85 nuclear track detector when etching them chemically with the use of three different techniques the conventional (water bath) and the novel (microwave and ultrasound). When irradiated the detectors with alpha particles and fission fragments. 2. Highlight the differences in the speed of developing tracks and the track density for etch techniques. 3. Calculate the etching track parameters (VB, VT, ϴC, η) for CR-39 and CN-85 for all the techniques used and make compare between them.

15

Chapter Two

Theoretical Background

Chapter Two Theoretical Background

(2-1) Introduction The development of SSNTDs began in the year 1958, when D. A. Young observed number of shallow etch pits in LiF crystal the name (etch tracks) was coined later for these shallow etch pits. D. A. Young observed these latent tracks in LiF crystal placed in contact (1 mm) with a uranium foil (238U) and irradiated with slow neutrons. The slow neutrons lead to fission of uranium nuclei followed by emission of fission fragments. These fission fragments traversed the LiF crystals and damaged the internal arrangements of atoms in the crystal structure, making these regions more chemically active than the surrounding undamaged region [47]. When the LiF crystal was treated with concentrated HF in glacial acetic acid (HF+CH3COOH) saturated with FeF3 for time intervals of 4560 minutes at 12 ˚C, the tracks were observable under an optical microscope. Fine channels are thus produced which accurately delineate the particle path and shows as a dark needle shaped tracks in a transparent detector under an optical microscope [48]. For example, an alpha particle with an energy of (6 MeV) creates about 150,000 of ion pairs in cellulose nitrates. Along the path of the alpha particle, then created zone enriched with free chemical radicals and other chemical species, this damage zone is called a latent track. The track effect exists in many materials. It is particularly pronounced in materials with long molecules, like cellulose nitrates or different 16

Chapter Two


polycarbonates, and such materials are the most convenient ones for application and detector manufacturing [49]. E.C. H. Silk and R. S. Barnes in the year 1959 unaware of the findings of Young, independently observed with the transmission electron microscope damaged regions in mica which marked the paths of heavy charged particles such as those from fission fragments or cosmic rays [50].

(2-2) Formation of a latent track Operation of the solid state nuclear track detector is based on the fact that a heavy charged particle will cause extensive ionization of the material when it passes through a medium. It produces narrow trials, damages at the level of molecular bands along their trajectory. Nuclear tracks formed by heavy ions are very small (only about 10 nm in diameter) [39]. Many theories have been proposed for the production of tracks by ionizing particles in solids, but none explains all the phenomena involved for both organic and inorganic materials. The basic mechanisms of energy loss are known. Fast moving charged particle energy, energy loss by excitation and ionization the atoms of matter. Ionization creates charge centres in solid. The ejected electrons, also called 𝛿-rays, can produce further excitation and ionization [51]. Organic materials, such as polymers, the excitation may break the long molecular chains and produce free radicals. As the ion slows to down, it starts picking up electrons, and thus its charge decreases. Close to the end of its path, atomic rather than electronic collisions are the dominant mode of energy loss. The result of atomic collisions is atom 17

Chapter Two


displacement and the creation of a vacancy [48]. The formation of the track in a polymer and a crystal is taking place as shown in Fig. (2-1). In other words, charged particle, flying through matter, loses energy and thus slows down in interaction with the fields of electron clouds and nuclei. Nature of radiation damage left after passing of ions through matter depends on matter characteristics, that are ordering of atoms, thermal and electrical conductivity, specific heat and sort of chemical bond in the matter. These characteristics determine, whether is it even possible to make a latent track. And matter is to be low conductivity or they are insulators [49].

Figure (2-1) Formation of a latent track [52]

(2-3) Characteristics of nuclear latent track The latent track of charged particle have following characteristics [52]: 18

Chapter Two


1) The track mainly consists of the damaged region along the path of the projectile due to displaced atoms. 2) The particle track is reactive centres towards chemical reagents due to presence of unstable centres along the trajectory. 3) The particle tracks are stable and can be viewed when required. 4) The track region has atomically continued along the path with a diameter of less than 10 nm. 5) The length of the damaged trail is equal to the range of the particle in the material.

(2-3) Types of Solid state nuclear track detectors (SSNTDs) The classifications of the SSNTDs types depend on two major classes is organic detectors and inorganic detectors, As well as classified into the naturally occurring detectors (like feldspar, mica, quartz, etc.) were used later. And man-made detectors were discovered (like CR-39, CN-85, LR-115, etc.) [53]. As in the table (2-1). A) Inorganic Detectors They are the detectors that don’t contain a hydrogen in their composition, and their molecules are linked by ionic bonds [54-55]. They are include; Orthopyraxene, zircon, apatite, sphene, olivine, quartz, muscovite mica, feldspar, etc. And glass detectors such as (phosphate glasses, vitreous glasses, soda lime glasses, silicon glass, borate glass, etc.) [53]. Figure (2-2a) shows the inorganic detectors and how to dislodge atoms [49]. B) Organic Detectors They are the detectors that contain a hydrogen in their composition, and their molecules are linked by covalent bonds [55-52]. It includes 19

Chapter Two


polymers such as; cellulose nitrate plastics (CN-85, LR-115), polyally diglycol carbonate (CR-39), bisphenol polycarbonate, (Makrofol, Lexan) etc. [53]. Figure (2-2b) shows the organic detectors and how their bonds are broken [49].

The figure (2-2) shows the damage from radiation (a) crystals (b) polymers [51]

(2-4) Detection thresholds of track detectors The detection thresholds of different solid state nuclear track detectors vary considerably and depend upon the atomic number (Z) and energy (E), as well as the velocity (v) of the charged particle. The parameter Z/β (where β = v/c) is normally used to characterise the minimum detection limit of a detector [56]. As in table (2-1). 20

Chapter Two


Table (2-1) Some nuclear track detectors, and its specifications[57-54]. Type of detector

Atomic composition

Manufacturer

Z threshold

Maximum detectable energy of alpha particle at the detector surface (MeV)

CR-39 (polyaallyl Diglycol carbonate, PADC)

C12H18O7

I. Page Moldings Ltd. UK.II. American Acrylics & Plastics, USA. III. Tastrak, c/o H H Wills Physics, Laboratory, UK. iv. Intercast Europe SpA, Italy

1

20

LR-115, CN-85, (cellulose nitrate)

C6H8O9N2

Kodak Pathé, France

2

4-4.5

C6H8O8N2

DNC (cellulose nitrate)

Russian Intercomparation, Russia

3.5-4

≥6

2-3

KAl2 (AlSi3O10) (F, OH)2

16

2

Soda lime glass

23SiO2:5 Na2O:5Ca O:Al2O3

16

20

Silica glass

SiO2

Zircon

ZrSiO4

Lexan, Makrofol E (bisphenol Apolycarbo nat)

C16H14O3

Muscovite mica

I. General Electric II. Bayer AG. Germany

16

21

Chapter Two


(2-5) The etching techniques for solid state nuclear track detectors (SSNTDs): (2-5-1) Chemical etching (CE) Chemical etching is a process of path formation, during which a suitable etching attacks the detector isotropically at a sufficient speed and the damaged regions along the ion trails (latent track) are preferentially dissolved, removed and get transformed into a hollow channel [48]. The radiation damage trails are more vulnerable to chemical reactions as compared to other bulk material because of the large free energy associated with the disordered structure. When these channels reach a width comparable to the wavelength of visible light, they act as strong scattering centres appearing black in the normal bright illuminated field and can be seen under optical microscope [58-59]. Each SSNTDs has its own etch parameters. The choice of etching solution, the temperature of the etching and the time of etching are the critical parameters which must be taken into consideration during the etching process. Etching solution should be so selected that the tracks with very small angles are produced and the surface of detector remains optically transparent. The etched tracks should also have regular geometric shapes [60]. The most common etching for plastics are aqueous solutions of NaOH or KOH with concentrations ranging from 1-12 N and temperatures in the range between 40-90 Co [49]. Somogyi et al., The chemical solution used to be the PEW-40 (15% KOH, 45% H2O, 40% C2H5OH) commonly used for (Lexan and Makrofol) [61], Glasses, mica and minerals were mainly etched with 47% HF acid. Short etching times 22

Chapter Two


are adequate for the observation of high the restricted energy loss (REL) particles and long etching times are required for low particles the restricted energy loss (REL) [62]. As shown in the table (2-2) [57-63]. The etched tracks depend on the following conditions [57]:  Types of track detectors.  The charge, mass and velocity of the incoming particle (or depend on the rate of Linear Energy Transfer (LET) of the charged particle over its trajectory).  The environmental conditions of exposed detectors.  The pre-etching treatments.  Type, concentration the chemical solution, temperature of etching. Table (2-2) Some etching conditions for organic and inorganic nuclear track detectors. Material of use detector

Cellulose nitrate (LR-115, CN-85, DNC) Polycarbonate (Lexan, Makrofol) Polyaallyl diglycol carbonate, PADC (CR-39) Cellulose acetate butyrate Polyvinyl acetate Muscovite mica Glass Zircon

Etching conditions (Etchant, molarity, temperature and time) NaOH, 1-12M, 40-70oC, 2-4 h NaOH, 1-12 M, 40-70oC, 20 min NaOH (KOH), 6M, 60oC, 12 h 6.25M, 70oC, 12 min 6.25M, 23oC, 200 h 48%, HF, 23oC, 10-40 min 1-48%, HF, 2-25oC, 1-2 min 11.5 g KOH+ 8 g NaOH, 200 220oC 48%, HF, 23oC, 24 h

Quartz

23

Chapter Two


(2-5-2) Electrochemical etching (ECE) The electro-chemical etching (ECE) method is first introduced by Tommasino et. 1970 [64]. Where the SSNTDs are stressed by electric fields (AC/DC) during the chemical etching [65]. Once the track has been formed, the electrical field at the tip of the conductive track needle can be many times greater (nearly MVcm-1) than the average electric field applied to the insulator. The highly stress gradients can initiate electrical phenomena, which, combined with the chemical action of the electrolyte, produce damage on the tree shape on the track tip. The detection sensitivity of SSNTDs is found to be improved with this method. Many researchers then wanted to have optimized this technique by studying the various combinations of CE and ECE and varying the electric field, frequency, etching [66]. This method has been very attractive, especially for the neutron dosimetry where the neutron-induced proton recoil tracks are easily discriminated from other background tracks. It's easy to track visualization and counting by enlarging tracks up to macroscopic sizes so as to be visible to the unaided eye [32]. (2-5-3) Microwave-induced chemical etching The frequency of the microwave radiation region, in the electromagnetic spectrum, lies between infrared and radio wave region frequencies (0.3 and 300 GHz). It is an established fact that microwave heating is very rapid, uniform and has a unique heat profile, which is not achieved by any other heating techniques. Electromagnetic waves may be absorbed by matter in many different ways depending on their wavelength and the matter state (gas, liquid, solid) [68]. 24

Chapter Two


The heat generated under microwave conditions is due to a dipole polarization mechanism. Since the dipole is sensitive to external electric fields, it tries to get aligned with the field by rotation [68]. The applied field provides the energy for this rotation, however, the frequency of rotation is not high enough to precisely follow the field. Therefore, as the dipole re-orientates to align itself with the electric field, the field is already changing and generates a phase difference between the orientation of the field and that of the dipole. Moreover, the wave energy alters the polarity from positive to negative with each cycle of the wave, which in microwaves, is about (2.5 *109 times per Sec). The phase difference causes energy to be lost from the dipole by molecular friction and collisions, giving rise to dielectric heating. This implies that a substance must possess a dipole moment to generate heat when irradiated with microwaves. This mechanism favors the rapid vibration and heating of the polarized molecules along the ion latent tracks, which results in a faster etching preferably along the polarized ion path, leading to quicker development of the nuclear tracks in SSNTDs [32]. (2-5-4) Ultrasonic chemical etching (UCE) It is similar to CE, but the etching gets constantly exposed to the ultrasound field during the etching time [68]. The alpha tracks were found to be larger with better discrimination from the background pits with improved selectivity of tracks. The vibration produced by the ultrasound source may excite the molecules of the detector material and the free radicals formed in the damaged regions through particle irradiations [69]. The excitation induced by ultrasound increases the latent energy of the damaged regions produced by the incident particles which get more degradation through etching than the damaged regions etched without 25

Chapter Two


ultrasound. Therefore, any increase in the degradation of the damaged regions leads to increase the track etch rate, which subsequently leads to increase the track's diameter and size. Advantages of this method over conventional chemical etching are: reduction in etching time, better clarity and homogeneous etching. However, this method is not being used as often as CE or ECE, because the track etch rate is not as high as the bulk etch rate leading to large size tracks and quick overlapping [70]. (2-5-5) Plasma etching (dry etching) Plasma treatment is a powerful technique to modify only the polymer surface. In this method, the liquid etching is replaced by plasma [71]. The main process is the reaction between the ions created in the plasma with material on the target surface. Glow discharge created by a radio-frequency (rf) generator wave within a low pressure gas or a monomer vapour leads to etching [72]. Brown and Liu had studied the etch with an argon rf-plasma discharge for the first time to locate and measure the size of the alpharecoil tracks in the mica [72]. This technique rarely used to develop the nuclear tracks in SSNTDs has reported a reduction in etching time by modifying the concentration of the etching with the addition of alcohol [73].

(2-6) Parameters track etching There are two factors affect the appearance of a track in detectors, they are the bulk etch rate velocity (VB) and the track etch rate velocity (VT).

26

Chapter Two


(2-6-1) Bulk etch rate (VB) The bulk etch rate VB is the rate at which the undamaged surface of the detector is being removed during chemical etching. Because the chemical reaction between the etching and the detector material, some molecules of the detectors are removed. The final effect is the removal of the material from the detector surface. During etching, the material is removed layer by layer and the thickness of the detector becomes smaller and smaller [62]. Generally, the following techniques are employed for the measurement of the bulk etch rate (VB) of the detector: (2-6-1-1) Thickness measurement method For the determination of VB the thickness of the detector is measured in selected points. The detector is then etched for fixed intervals of time (Δt) and the thickness is measured after each successive etching step. 𝑉𝐵 =

𝛥𝑥 2𝛥𝑡

…………………………(2-1)

Where Δx is the thickness variation after etching time Δt [74]. (2-6-1-2) Track diameter measurement method If VT/VB >> 1 as in the case of fission fragments from a

252

Cf

source in CR-39, the track diameter measurement technique can be applied for the determination of VB as in equation [62]. Dff = 2h√

𝑝−1

……..……………………(2-2)

𝑝+1

27

Chapter Two


Where Dff is the diameter of fission fragments, p = V T/VB and (h) is the thickness removed from both sides of the detector during an etching time t. If p >> 1 the above equation. Can be written as Dff=2h (h=VBt)……………………. (2-3a) Dff= 2VBt………………………….. (2-3b) VB= Dff /2t…………………………. (2-3c)

(2-6-1-3) Mass Change method This is done by measure the change in the mass of the detector (Δm) before and after etching the detector and can be calculated from the following equation: VB=

∆𝑚 2𝐴𝑃𝑡

……………………………… (2-4)

Where A is the surface area, (ρ) is the density of the detector and (t) is the etching time [48]. (2-6-1-4) Measurement method the track's diameter-length (Le-D) The bulk etch rate (VB) can be calculated by using the method of direct measurement of the removed layer thickness (h) from the detector. This method is difficult, compared to other methods in the process of VB calculating, because it requires getting images of the track formed in the detector, and an accurate measure of the track diameter (D) and length (Le) empirically directly. The measurements must be performed during the first phase of the growth track, and is the stage a regular the cone pattern until the arrival of the head track to the end of the range of 28

Chapter Two


the particle in the detector. (VB) is calculated of the following equation [75]. 𝑉𝐵 =

𝐷2

[1 + √1 + 4𝑡𝐿𝑒

4𝐿𝑒 2 𝐷2

]………… (2-5)

(𝑉 −𝑉𝐵 )

𝐷 = 2𝑉𝐵 𝑡√(𝑉𝑇

…………….…... (2-6)

𝑇 +𝑉𝐵 )

Where: (Le) track length. (D): the track diameter. (t): etching time. (2-6-2) Track etch rate (VT) The rate at which the latent track is etched is called track etch rate in other words, it is the rate of detector etching along the track of the particle. The track etching process involves attack of the etching along the track. Track etch rate depends on the amount of damage located in the trace region. The track etch rate (VT) should be always more than the bulk etch rate (VB) for efficient track viewing under optical microscope [62]. 𝑉 1+( 𝐷 )2

VT=VB

𝑉𝐵 𝑉𝐷 2 1−( ) 𝑉𝐵

…………….……….. (2-7)

Where VD rate of the track diameter (VD = ΔD/Δt)

29

Chapter Two


(2-6-3) Etching rate ratio (V) It's the ratio between the track etch rate (VT) to bulk etch rate (VB), and it is expressed in the following equation [76]. 𝑉=

𝑉𝑇 𝑉𝐵

….…………………..……. (2-8)

(2-6-4) Critical angle of etching (θC) Fig (2-3) which shows us the three probabilities of the angle that the particle incident on the detector relative to the critical angle. a) Represents a particle incident at an angle θ larger than the critical angle i.e θ>>θc. In this case the latent track never be developed by etching the detector. b) Represents a particle incident at an angle θ equal to the critical angle θc i.e. θ = θc in this case the latent track was fail to developed inspite of being formed. c) Represents a particle incident at an angle θ smaller than the critical angle θc, i.e θ C (e.g. Normal incidence), (b)  < C and, (c)  =C (i.e. Critical angle) [77]

(2-6-5) Etching efficiency (η) The value of the etching efficiency depends on the track etched rate, velocity VT and the bulk etched rate velocity VB. The efficiency can also be defined in terms of the critical angle as follows: [78] η = 1-SinθC…………………………. (2-10a) Or η = 1- (VB/VT)………………………. (2-10b) Or η = 1- (1/V)………………………… (2-10c)

31

Chapter Two


(2-7) Track Geometry Geometry nuclear track depends on the angle of incidence particle (θ), which made with the surface of the nuclear track detector, any θ ˃ θC and V ˃ 1, as in the following equation [79]. θC=Sin-1(1/V) ≤ θ ≤ 90 The geometry of track etching depends on chemical etching solution along the particle track at a linear rate VT, and a general attack on the etched surface and on the interior surface of the etched track at a lesser rate VB, VT ˃ VB. The parameters used to describe the geometry of the etched track [80]: 1. The full length of the latent track (L) 2. The thickness of the surface removed by etching (h). 3. The diameter of the etch pit (D).

(2-7-1) Vertical incidence (θ = 90̊) The track etching geometry for a particle penetrating a detector surface perpendicularly, as shown in Figure (2-4). It is assumed that both VT and VB are constant for isotropic non crystal solids. The diameter of the track cone of the etched surface, D and its length L depend on the competitive effects of (VT) and (Vb) [81]. L = (VT – VB) t…………………….. (2-11) And

32

Chapter Two

D =2 VB t (

Theoretical Background 𝑉𝑇 − 𝑉𝐵 1/2 𝑉𝑇 +𝑉𝐵

)

…………………. (2-12)

Figure (2-4): Three phases in the track development. (I) Is the initial detector surface, O and E are the entrance and end points of the particle path R, (1) Conical track; (2 and 3) the track wall is partially conical and partially spherical; (4) the track is fully spherical [39].

(2-7-2) Incidence at an angle (θ≠90̊) If the particle is incident at the italics angle θ with respect to the detector surface, the etch cone opening will be an ellipse as shown in Figure (2-5). And will be in three phases [81-82]: 1. Conical Phase (X1). 2. Transition Phase (X2). 3. Spherical Phase (X3).

33

Chapter Two


Figure (2-5): Three phases in the track development. (I) Are the initial detector surface, O and E are the entrance and end points of the particle path, (1) Conical Phase (X1) (Y1, t1), (2) Transition Phase (X2) (Y2, t2), (3) Spherical Phase (X3) (Y3, t3) [39].

(2-8) CR-39 detector One of the most commonly used nuclear track detectors is the CR39 detector which was discovered by Cartwright et al (1978) and is based on (Polyallyl diglycol carbonate) (PADC) and it was called CR-39 (Columbia Resin) [83]. Its density is (1.31g. Cm-3), and the amount of ionization (70.2 EV) [84], Its chemical form is C12H18O7. This plastic detector is made by polymerization of the oxide-2, 1-ethanediyl, di-2-propenyl ester of carbonic acid. It contains two of monomer ally functional groups [CH2 = CH – CH2 –] and as in the following composition in figure (2-6) [85].

34

Chapter Two


Fig. (2-6) The chemical form of CR-39 plastic [85]. There are very few materials that can compete the sensitivity of CR-39 track detector, efforts are on to devise new materials which can exceed the sensitivity of CR-39. Tyler found in 1981 that the sensitivity and characteristics of pre-etching of CR-39 detector are possible improved by adding 1% of substance (dioctyl phthalate), the new detector is named CR-39 (Dop). Also, it was discovered detector developer for CR-39 called SR-86 which is made from (diethylene glycolbic (Allyl solvent)). SR-86 is polymer participants from CR-39, the SR-86 polymer has sensitivity higher than that of the CR-39 track detector, but has a low use period [86]. The CR-39 has some specifications as [87]:  Optically transparent.  Very sensitive to radiation.  It has a lower detection threshold.  Highly isotropic and homogeneous.  It is not affected by weather factors, humidity, when stored for a long time.  This polymer is resistant almost to all solvents, and to the heating.  After radiation damage has broken the chemical bonds. 35

Chapter Two


(2-9) CN-85 Track detector The track detectors Cellulose Nitrate CN-85 have been extensively used in a variety of studies, its density is 1.42 gm/cm3 and its the chemical formula is C6H8O9N2. CN-85 is manufactured by Eastman Kodak Company, and considered suitable for the detection of particles involved in radon studies [88-89]. Where cellulose nitrate (CN) is plastic detectors of which commercial varieties are available as CN-85 and LR-115 have an upper limit to the registration of α-particles at energies of roughly 4 to 6 MeV (depending on the etching conditions) [60].

(2–10) Applications of solid state nuclear track detectors The nuclear track detectors are used almost in all fields of nuclear chemistry, nuclear physics and also for biomedical and Environmental studies and health effects, this topics of great interest to the workers current track detector. The nuclear track detectors are used in following diverse fields [39-90]: i.

Nuclear physics, and technology: - Fission track dating, uranium and thorium exploration, alpha estimation in waste water fields. Heavy ion reactions, astrophysics and cosmic rays, search for super heavy elements.

ii.

Environmental and health physics:- Radon dosimetry, neutron dosimetry, exposure at spacecrafts.

iii.

Biomedical Science:- Boron neutron capture therapy, alpha content of blood, lead content in the bones.

iv.

Technological sciences :- Nucleopore filters, magnetic nanowires.

36

Chapter Two


(2-11) The Americium The americium is a radioactive chemical element with symbol (Am) and atomic number (95), this member of the actinide series in the periodic table [91]. Americium was first produced in 1944 by the group of Glenn T. Seaborg at the University of California [92]. Americium is an artificial element, and thus a standard atomic mass cannot be given. Americium has (19) radioisotopes, with the most stable being a half-life of (7,370) years, and

241

243

Am with

Am with a half-life of (432.2) years.

All of the remaining radioactive isotopes have half-lives that are less than 51 hours, and the majority of these have half-lives that are less than (100 min) [93]. (2-11-1) Americium-241 (Alpha source) Americium, atomic number (95) and number mass (241), It consists when uranium-238 was bombarded with helium [91], as in the equation (2-13). 238

U + 4He → 241Pu + n…………….. (2-13)

The decay 241Pu with a 13.2 y half-life through emission (β-), to be 241

Am, as in the equation (2-14) [94]. Pu → −

241

(β ) 13.2𝑦

241

Am……………….. (2-14)

The plutonium present in spent nuclear fuel contains about 12% of 241

Pu, because it spontaneously converts to 241Am [95]. The americium decays with a half-life of (432.2) years, and with

emission alpha particle and gamma and turn into a 237Np, as in Figure (27) [94]. 37

Chapter Two


The gamma rays low energy of (0.0597MeV) were accompany the alpha decay. While the energy alpha particles are (5.49-Mev) [96].

Fig (2-7) Decay Scheme of 241Am The alpha range at traversing in matter loses the energy in ionizing collisions. Can estimate the range alpha particle from Integration inverse the stopping power (-dE/dx). As in the equation (2-15) [21]. 𝑅

𝐸

𝑑𝐸 −1

𝑅 = ∫0 𝑑𝑥 = ∫0 (− ) 𝑑𝑥

𝑑𝐸 ………… (2-15)

Where (R) the range of particle in matter, (- dE/dx) middle rate of energy lost by the charged particle in the unity of the distance from the track. The range extent of alpha particles in the air, can be calculated from the following equation (2-16) [97]. 3⁄ 2 ………….……

𝑅𝑎𝑖𝑟 (𝑐𝑚) = 0.318(𝐸)

Where: (E) particle energy incident.

38

(2-16)

Chapter Two


(2-11-2) 241Am-Be neutron source Neutrons can be produced from different sources such as nuclear reactors, isotopic neutron sources and particle accelerators. Low-intensity neutron sources prepared from a mixture of an alpha particle with beryllium, or high-energy gamma-emitting radioisotopes and beryllium produce neutrons [98]. The oxide of

241

Am pressed with beryllium is a neutron source.

Where americium as the alpha source, and beryllium produces neutrons from the (α, n) nuclear reaction, as in equation (2-17) [99]. 9 4𝐵𝑒

+ 42𝐻𝑒 →

12 6𝐶

+ 10𝑛 + 𝛾…….. (2-17)

The (241Am-Be) neutron sources used in nuclear medicine, radiotherapy and industry. Fast neutron were be used in radiobiological research and radiotherapy, thermal neutrons were be used in neutron activation analysis [100].

39

Chapter Three

Experimental Technique

Chapter Three Experimental Technique

(3-1) Introduction: This chapter includes the: 1. Preparation of solid state nuclear track detectors and who making them ready to exposure with alpha and neutron sources. 2. The locations from which the studied soil samples were be collected and the technique of their preparation and coding samples. 3. The relations used in the results calculations. 4. In addition to the materials and instruments used in the execution.

(3-2) collection and preparation of soil Samples: Fife subsurface samples of soil were collected from a very important sites of meeting and presence of students, these sites were distrbuted in all the area of Al-Mustansiriyah University. A (30grams) of each sample was taken at a depth of (20 cm) below the surface, the samples then were be cleane and dry in an oven at (150oC) for 24 hours because the large humidity in Baghdad at the time of samples collection, finally they were powdered with (home mill) and sifted by special sieve (mesh :630 micron).

(3-2-1) test sieve Sieving is the separation of fine material from coarse material by means of a meshed, sieve is a screening medium (mesh) with openings of uniform size and shape mounted on a rigid frame made of brass and stainless steel in a cylindrical configuration. 40

Chapter Three


Sieve brand Restch made in (Germany) supplied from (Retsch GmbH), have a diameter of (200mmx50mm) and opening size of (630 micron) were be use in the research for particle size analysis. Figure (31) shows a picture of the using sieve.

figure (3-1) test sieve.

(3-3) Samples sites and coding: The five locations from which the soil samples were gathering and their longitude and latitude coordinates were identified using GPS system and the codes of the samples were be listed in table (1). Figure (1) shows these sites on the map of Al-Mustansiriyah University.

Table (1-3) the samples codes and their gathering locations. No.

Sample code

Sample location

longitude

latitude

1

S1

Near the student cafeteria

33˚22ˊ04"

44˚24ˊ15"

2

S2

University Stadium

33˚22ˊ05"

44˚24ˊ11"

3

S3

Centre of college of education

33˚22ˊ00"

44˚24ˊ07"

4

S4

Centre of college of arts

33˚22ˊ00"

44˚24ˊ09"

5

S5

Centre of college of science

33˚22ˊ02"

44˚24ˊ09"

41

Chapter Three


Fig (3-2) samples collection sites on Al-Mustansiriyah University map.

(3-3-1) Electric oven: Electric oven brand (Luxell) manufactured in Turkey, its temperature up to (1500C˚) is being used in our research to dry soil samples. Figure (3-2) shows the used oven.

42

Chapter Three


Fig (3-3) electric oven used to dry soil samples

(3-4) pressing the soil samples: Few grams (2gm) of the fine soil prepared powder were be mixed uniformly with a high purity laboratory starch (C6H10O5)N as a connecting material, the mixture then would be pressed by hydraulic press into mini disc with a thickness of (2mm) and a diameter of (2cm), the disk then inserted between two slices (1x1cm2) of solid state nuclear track detectors (CR-39) as sandwich of (detector-sample-detector).

(3-4-1) Connecting material (starch): A starch or amylum trade (SCR) supplied from sinopharm chemical reagent Co. Ltd., were be used to connect the soil samples materials, it is a carbohydrate consisting of a large number of glucose units joints by glycoside bonds. Its chemical symbol is (C6H10O5)n and insoluble in water. A high-purity starch laboratory of (99.9%) and a density of 1.5 /cm3 were be used, it is mixed with soil samples which wanted to be pressed by percentage of 8:2.

43

Chapter Three


(3-4-2) hydraulic Press: A manual hydraulic press (Herzog) type made in germany provide with a barometric gage and with a compressive force ranging between (1-20 tons) were be used to compress the samples into mini disk, with the help of a locally made steel mold of a (2cm) in diameter. Fig (3-1) shown the using press and cast.

Fig (3-4) the hydraulic press and cast

(3-4-3) Solid state nuclear track detectors: (3-4-3-1) CR-39 detector: A plastic Sheet of (30 x 30) cm2 area with (500 µm) thickens of CR39 solid state nuclear track detector supplied by "Pershore Moulding LTD Co. UK" were be used. The required slice area (1x1) cm2 were be prepared by cutting the sheet by blade into the wanted pieces. 44

Chapter Three


CR-39 detector were be used in our present work because it's low detection threshold, high registration sensitivity, it has the ability of use for long period of exposures without any fading, and its efficiency in the detection of alpha particles and fission fragments.

(4-3-3-2)CN-85 detector: A plastic sheets of (15x10) cm2 area and (12µm) thickens of (CN-85) solid state nuclear track detector of trad (Kodak) supplied from the japan dosirad laboratory were be used in this research. Cn-85 detector have many applications because its very sensitive to the energetic alpha-particles since they cause intense damage trail as it passing through them. Thus its widely used for detecting and measuring: 1. Detection and dosimetry of α-particles. 2. Detection and dosimetry of thermal and epithermal neutrons. 3. Detection and dosimetry of very fast neutrons. In this case spallation fragments produce the tracks. 4. Auto radiography of alpha radioobjive objects.

(3-5) Irradiation of the soil samples with neutrons: The detector and sample sandwiches were exposed to a stream of fast neutrons emitted from americium-beryllium (241Am-Be) neutron source to fission the heavy radioisotopes in soils. The period of irradiation to the neutrons were be (7 days) to reduce the statically errors and insure that most of the uranium atoms in the samples will be fission in this period. The thermal neutron will split the uranium (238U) into minerals of interest, and some fission fragments are shooting into the track detector according to the interaction [50]: 45

Chapter Three


238 92U

+10n (fast) → 23992U*→ fissions

Fig (3-3) shows the direction of fission fragments of the uranium in the soil sample existing between two track detectors when irradiated with neutron source. Path of fission fragment

Uranium atom

Detector

500 μm Sample 500 μm Detector

(3-5) Fission Track occur in sandwich of soil sample and two slices of solid state nuclear track detector

(3-5-1) Neutron source: A plane (241Am-Be) manufactured by USA, and of recent 12Ci Activity, the iceberg neutron (3*105 n/cm2.s), The torrent neutron (1.844*1011 n/cm2.s) in (7 days), is provided and used in the present work as figure (3-2). It is one of alpha initiated radio isotopic sealed neutron source and most widely (the Americium- 241 alloyed with Beryllium). The alpha particles from Americium have sufficient energy to react with Beryllium, causes emission of neutrons according to the following reactions [42]: 241 9 4Be

95Am

  237 93Np + 42α

 +42 He 

12

6C

+ 10n + 5.71 MeV

(3-6) irradiation of the track detectors with alpha: Slices of two types of solid state nuclear track detectors (CR-39) and (CN-85) were be cut by blade into squares of (1×1 cm2) and 46

Chapter Three


irradiated to alpha particles emitted from americium (241Am) point source by putting each detector at a distance of (2cm) in a geometry of 180° against the source using as shown in the figure (3-6).

Fig (3-6) the design used to irradiate the detectors with the alpha particles emitted from americium source.

(3-6-1) Alpha source (Americium-241): A root of (Americium-241) source with the activity of (10µci) (370kBq) manufactured by (Amersham Buchler), Energy of intense alpha particle [5.486 MeV], Half-life (432.17y), were be used to irradiate the detectors. Figure (3-7) shows a picture of the using source.

Figure (3-7) (Americium-241) source. 47

Chapter Three


(3-7) Dose calculation: The detectors were being irradiated at three different times (10, 20, 30 second) in order to get different doses of alpha particles. The doses to which the detectors were exposed would compute by the Microsoft program (Rad pro calculator version 3.26) designed for calculate the dose-rate of the radioisope source by input its activity and the distance between the source and the detector. The doses for each time were shown in the table (2-3). Table (2-3) alpha doses calculated according to times of irradiation

Dose (µSv) x10-2

Dose-rate (µSv/hr) Tim of irradiation(sec)

3.67703

10

1.021

20

2.042

30

3.064

(3-8) Chemical etching: The detectors were chemically etching after the irradiation in a NaOH solutions with normality of 6.25N for CR-39 and 2.5N CN-85. Three techniques were being used to synths the detectors:

(3-8-1) Preparation of the Etchant solution: A base solution of sodium hydroxide pellets (NaOH) trade has been used for the chemical etching process in this research. The etchant solution was prepared by applying the following equation:

(3.1) Where:W: is the weight of NaOH needed to prepare the given normality. Weq: is equivalent weight of NaOH  40. 48

Chapter Three


N: is normality equal to 6.25 for CR-39 and 2.5 for CN-85. V: volume of distilled water  250 ml. The (NaOH) pellet were be solved in distilled water with the help of hot plate stirrer to get a homogeneous solution, the solution then fill a volumetric flask with size of (500ml) and

immersed the hanging

detectors inside it. This is done by placed the detectors inside the etching solution after commenting them by Teflon wire, the volumetric flask then putt in the choosen device to start etching process.

(3-8-1-1) hot plate Stirrer: It is electromagnetic machine with magnetic bar which were used to dissolve materail using heat and magnetic force. A hot plate strirrer trade (lab tech) supplied from daihan lab tech, co. Ltd. made in (Korea) were be used Widely applied in biology, medicine, chemistry, chemical engineering and other related fields. It Constantly adjustable stirring speed and heating temperature.

Figure (3-8) hot plate strirer

49

Chapter Three


(3-8-2) Chemical etching techniques: (3-8-2-1) Chemical etching with water bath: The volumetric flask containing the etchant solution and the detectors would be putting inside the water bath tank at a temperature of (70Cº) and (60C˚) for different times of interval.

(3-8-2-1-1) water bath device: A water bath is a laboratory device made from a container filled with heated disttled water and supplied with heat source accompanied by a thermostat for heating water and solvent to the desired temperature. A water bath of trademark (HH-2), made in china, operates over a range of (10-100 Cº) to heat the etching solutions to the desired temperature. A picture of the water bath were be shows in figure (3-9).

Fig (3-9): Water bath device.

(3-8-2-2) Chemical etching with ultrasound waves: This is done by repeat the previous operation except putting the detectors inside the etching solution in an ultrasound bath instead of a 50

Chapter Three


water bath at a temperature of 70C˚ and 60C˚

for a selected time

intervals instead of the water bath.

(3-8-2-2-1) ultrasonic cleaner device: Ultrasonic cleaners are came into use as relatively inexpensive appliances in about 1970. Its used "cavitation bubbles" induced by high frequency pressure (sound) waves to motivate a liquid in the cleaning. The device consists of a tank containing a suitable solution (aqueous or organic). The generator of the ultrasound is a transducer built into the tank, or lowered into the fluid it, produces ultrasonic waves in the fluid by changing the tune or harmony size with the electrical signal oscillating at ultrasonic frequency. This creates compression waves in the liquid of the tank which crack the liquid apart, leaving behind many millions of vacuum bubbles (cavitation). These bubbles break down with enormous energy; temperatures and pressures on the order of (5,000ºK) and (20,000 lbs /inch2) are achieved.

Figure (3-10) ultrasounic cleaner device using in our research.

Our using device is manufactured in China, supplied from (Guangzhou lingchen trading Co. Ltd.) model: PS-D40, its unit size is (330*270*260mm), its tank size is ( 300*240*100mm), its operating 51

Chapter Three


voltage is (AC100-120V) with a frequency of (50-60HZ), its ultrasonic power is (240W) and frequency of 40 KHz. The device is supplied with a timer ranging from (1-30 minutes) period. And having a tank capacity of 7 liter.

(3-8-2-3) Chemical etching with microwaves: In this technique the detectors with the etching solution were placed in special test tube then putting in a laboratory microwave at a temperature of 70°C for a selected time intervals.

(3-8-2-3-1) laboratory microwave device: The device type of (Monowave 300) from the production company (Anton Parr) Austrian, making in a year (2012), which is a hightechnology device which has a touch screen can be controlled in a device. Maximal temperature to reach them (300C˚) and power (850W). The Bottles contain size (10mL), (20mL), (30mL), manufactured materials, Borosilicate glass, silicon carbide. Is a high performance microwave reactor specially designed for small scale microwave synthesis applications in research and development laboratories.

Fig (3-11) laboratory microwave device 52

Chapter Three


(3-9) Cleaning and drying the detectors: After the detectors are taken out from the etching solution they are washed and dried. They will be washed with distilled water then immersed in a be ionized water finally they are wiped with methanol by special paper in order to cleansing the detector well from the etching solution and get a good image to view and calculate the tracks of alpha and fission tracks. After the detectors out of the volumetric flask, they will be washed with distilled water then a be ionized water then wipes with alcohol in order to cleansing the detector well from the etching solution and get a good image of tracks. De ionized water: Also known as de mineralized water, almost all of its mineral ions removed such as sodium, calcium, iron, and copper, and anions such as chloride and sulfate.

(3-10) viewing the detectors: The tracks of alpha and fissions produced in the etched detectors are viewed under an optical microscope brand N-200M with a magnification of (400X). The microscope is connected to digital camera and computer to store the pictures of the viewing detectors.

(3-10-1) Track density measurement: The fission track density in solid state nuclear track detector used measured by counting the number of track in (10) views of (0.0486 cm2) area for each detector as in figure (3-12) then the track density would be calculated from the following equation:

53

Chapter Three


Fig (3-12): Optical microscope.

(3-10-2) Optical microscope: Optical

microscope

of

Novel

type

model

(N-200M)

industrialization in Korea is used to view and magnify tracks of fission fragments generated in the detectors. Its binocular head 45 inclined, 360 rotatable. Supplied with two different eyepiece magnifications, wide filed 10X and plan field 16X, and four objective magnifications 4x, 10x, 40x(S), and 100x(S, Oil). Thus its total magnifications started from 40x to 1600x. In our study we use 10x eyepiece and 40x objective magnifications i.e. 400x total magnification.

(3-10-3) Digital Camera: Camera device consists of two parts:  Industrial Digital Camera: type model (Toup CamTM), model number (UCMOS06100KPA-U-NA-C-SQ-NA), USB2.0 DC, 54

Chapter Three


Voltage 5v and electric current 250 mA.  Microscope Lens Adapter: type model (Toup CamTM), model number (FMA050), 50X magnification , fixed focal length ,fit 1/2 ~ 1/3 size sensor as shown in figure (3-13).

Fig (3-13): Camera installation user. (3-11) Sensitive balance: The Sensitive balance of (Mettler Garantia AE163) type, industrialization in Switzerland is used to weight the samples.

Figer (3-14) Sensitive balance 55

Chapter Four

Results and Discussion

Chapter Four Results and discussion (4-1) Introduction: This chapter includes a demonstration of the results and their calculations have been reached in this research, in addition to the dissuasion of the outcomes, and the conclusions we deduced at the end of the research, and the future works we advise to do it by the other following researchers. This research try to estimate the appropriate time for etching alpha and fission fragments latent tracks originated in two organic and sensitive solid state nuclear track detectors (CR-39 and CN-85) using chemical etching induced with three different techniques; water bath, microwave and ultrasound, In order to recognize the effects of these techniques on fasting the process and shortening the etching time, besides developing the clearest track shape and increasing the number of the latent tracks appearance. Some related calculations have also be compute in each technique for the two detectors such as; bulk etch rate (VB), track etch rate (VT), etching rate ratio (V), critical angle of etching (ϴC) and etching efficiency (Ƞ). The comparison between the differentiations of these results will be used to discuss the best outcome.

(4-2) Time estimation of developing latent track by chemical etching: Chemical etching is the most widely used method from many other methods for fixing and enlarging the latent tracks originated in the solid state nuclear track detectors by (108) time their original size. 56

Chapter Four


The conditions of the Chemical etching are depending on many parameters like; etching time and, type, normality and temperature of the etching solution. Many researches on these parameters were be done to optimal the etching conditions in order to fast the etching time with best surface quality in addition to increase the number of the latent tracks developed and decrees the number of face tracks depends. In our research we use two modern devices (microwave and ultrasound) to estimate the optimum chemical etching time of alpha latent tracks originated by exposed CR-39 and CN-85 detectors to (Am-241) alpha source, and fission fragments latent tracks originated by irradiated soil samples sandwiched with CR-39 detector to neutron (Am241-Be) source.

(4-3) Time estimation of alpha latent tracks: (4-3-1) Time estimation of alpha latent tracks in CR-39 detectors: a. CR-39 detector in touch with alpha source: First we start to put (CR-39) track detector directly on the (Am241) alpha source (or in touch with the source) for 30 second; this would make the detector irradiated with the total energy of the source which is (5.495MeV). Then it will be etched with (NaOH) of 6.25N for 20 second etching time in water bath device, the enlarged view of the etched detector under the optical microscope showed a huge tracks with noticeable gradual track densities from the largest numbers in the center to the lowest number in the periphery. Figure (4-1) shows a picture of a view of the enlarged tracks originated in the CR-39 detector when exposed in touch with (Am-241) alpha source.

57

Chapter Four


Figure (4-1) a view of enlarged tracks originated in CR-39 detector after exposed in touch with (Am-241) alpha source.

b. CR-39 detector at a separation distance from alpha source: The CR-39 detector were exposed secondly to alpha from (Am241) at a selected specific distance between them, the main emitted alpha energy is (5.495MeV), but the incident energy on the track would be decreased to (3.4MeV) by placed in air the track detector at a distance of (2cm) under atmospheric pressure from the source, the energy of alpha at a distance of (2cm) from the source were be calculated from alpha range equation (2-16). The detectors were exposed to different doses this is done by changing the time interval of irradiation. The detectors then would be etched chemically with the three devices at the same etching solution (NaOH), same normality (6.25) and the same temperature (70Cº) but at different etching times in order to achieve the optimum one for each device. 58

Chapter Four


(4-3-1-1) chemically etching with water bath device: The irradiated CR-39 track detector with alpha particles for different three doses or different times (10, 20, 30 second) would be etched for various times until reaching the optimum one. Detector was start to be etched starting from 10 minutes but the tracks was started to appear clearly at 30 minuet, thus only eight times were be considered in our research starting from (30 minuet) till (240 minuet) with interval of (30 minute) in between. The utilized etching times, the track densities for the three times of irradiation appeared in the detectors, in addition to their maximum and average were listed in the table (4-1). Table (4-1) track densities in CR-39 detector at different doses and various etching times when using water bath device. Etching Time Densities (ρ no /mm2) at the different doses (Min) Time of exposure to alpha source Alpha (10 Sec) Alpha (20 Sec) Alpha (30 Sec) 30 637 1003 1846 60

644

1050

2288

90

720

1304

2208

120

732

1367

2211

150

823

1300

2122

180

681

1254

2034

210

670

1216

2018

240

654

1212

1979

Average

695.1

1213.2

2163.2

Max

823

1367

2288

The increasing of the track densities with the developing of the latent tracks and the enlarging of them against the increasing of the 59

Chapter Four


etching time can be clearly observed in figure (4-2), which shown a picture of four views at different selected etching times (30, 90, 15, 240 minutes) of a detector irradiated for (20 second) imaged with optical microscope of x40 magnification.

Figure (4-2) views of CR-39 detector etched chemically at (30, 90,150, 240) minutes with water bath. (4-3-1-2) chemically etching with microwave device: The irradiated CR-39 track detector with alpha particles for different three times (10, 20, 30 second) would be etched chemically with the use of microwave emitted from a laboratory microwave device operating at a frequency of (2.45GHz), the detectors etched for different times until reaching the optimum one. The time at which the latent tracks started to appear would be (10 minute). Four etching times were used with interval of (10 minute)

60

Chapter Four


between them (10, 20, 30, 40 minutes) in order to achieve the optimum time. The increasing of the track densities with the developing of the latent tracks and the enlarging of them against the increasing of the etching time can be clearly observed in figure (4-3), which shown a picture of four views at different selected etching times (10, 20, 30, 40 minute) of a detector irradiated for (20 second) imaged with optical microscope of x40 magnification.

Figure (4-3) views of CR-39 detector etched chemically at (10, 20, 30, 40) minutes with microwave device. The exercised etching times and the track densities became clear in the detectors for the three irradiation times of the detectors or different alpha doses, in addition to the maximum and average of the track densities were shown in table (4-2).

61

Chapter Four


Table (4-2) track densities in CR-39 track detector at the different doses and various etching times using microwave device. Track density (no /mm2) of alpha particles Etching Time Time of exposure to alpha source (min) Alpha (10 Sec) Alpha (20 Sec) Alpha (30 Sec) ) ) 10 654 1124 1453 20

670

1247

1466

30

830

1206

1683

40

708

1057

1630

Average

715.5

1158.5

1558

Max

830

1247

1683

(4-3-1-3) chemically etching with ultrasound device: The irradiated CR-39 track detector with alpha particles for different times (10, 20, 30 second) etched chemically with the use of ultrasound waves emitted from a laboratory ultrasonic cleaner device operating at a frequency of 40KHz, were be etched for different Progressive times with an interval of (30 minutes) between them, in order to reach the optimum time. Eight times were used (30, 60, 90,120, 150, 210, 240) minutes to achieve this. The increasing of the track densities with the developing of the latent tracks and the enlarging of them against the increasing of the etching time can be clearly observed in figure (4-4), which shown a picture of four views at different selected etching times (30, 45, 60, 90 minutes) of a detector irradiated for (20 second) imaged with optical microscope of 40X magnification.

62

Chapter Four


Figure (4-4) views of CR-39 detector etched chemically at (30, 90, 150, 240) minutes with ultrasound device. The applied etching times and the track densities appear in the detectors for the three times of irradiation, in addition to the maximum and average of the track densities were illustrated in table (4-3). Table (4-3) track densities in CR-39 track detector at the different doses and various etching times using ultrasound device. Etching Time Track density (no /mm2) of alpha particles (min) Time of exposure to alpha source Alpha (10 Sec) Alpha (20 Sec) Alpha (30 Sec) 30 614 1212 1672 60

658

1271

1874

90

689

1267

2067.9

120

757

1345

1975

150

640

1265

1814

180

672

1255

1790

210

662

1204

1778

240

638

1088

1721

63

Chapter Four


Average

666.2

1239.5

1836.48

Max

757

1267

2067.9

(4-3-2) Time estimation of alpha latent tracks in CN-85 detectors: The CN-85 track detectors were exposed to alpha particles emitted from (Am-241) source with energy of (3.4MeV) by placed the detector at a distance of (2cm) from the source. The detectors were exposed to different doses by changing the time period of irradiation. The detectors then would be chemically etched with the three devices at the same etching solution (NaOH), same normality (2.5) and same temperature (60Cº) but at various etching time in order to reach the optimum time for this detector at each device. (4-3-2-1) chemically etching with water bath device: The irradiated CN-85 track detector with alpha particles for different three doses would be etched for different times in order to reach the optimum one. Seven considered times were being used starting with (15 minuet) ending with (45 minute) with interval of (5 minute) in between. The differences in the size and shape of the tracks and its number or its track density relative to the etching time would be shown clearly in figure (4-6) below, figure shown a picture imaged with optical microscope of 40x magnification, its include four views of tracks developed in a detector irradiated with (20 second) and etched at different selected four etching times (15, 25, 35, 45 minutes).

64

Chapter Four


Figure (4-5) four views of CN-85 detector etched chemically at (15, 25, 35, 45) minutes with water bath. The utilized etching times and the track densities for the three times of irradiation appeared in the detectors, and their averages and maximum were listed in the table (4-4). Table (4-4) track densities in CN-85 track detector at the different doses and various etching times using water bath device. Etching Time Track density (No/mm2) of alpha particles (Min) Time of exposure to alpha source (10 Sec) (20 Sec) (30 Sec) 15 620.62 767.97 1221.27 20

688.09

994.91

1301.45

25

709.87

1025.78

1437.9

30

758.89

1216.41

1434.27

35

775.23

1091.14

1470.58

40

682.64

1056.64

1083.87

45

673.56

911.4

1056.6

65

Chapter Four


Average

701.27

1009.17

1286.56

Max

775.23

1216.41

1470.58

(4-3-2-2) chemically etching with microwave device: The irradiated CN-85 track detector with alpha particles at different three doses would be etched chemically for four times (5, 10, 15, 20 minuet) with the use of laboratory microwave device in order to reach the optimum time. The utilized etching times and alpha track densities appeared in the detectors, and their averages and maximum were listed in the table (45). Table (4-5) track densities in CN-85 track detector against different doses and various etching times using microwave device.

Etching Time (min) 5 10 15 20 Average Max

Track density (no /mm2) of alpha particles Time of exposure to alpha source (10 Sec) (20 Sec) (30 Sec) 576 986 1080 659 1042 1402 685 942 1565 657 979 12701 644.2 987.2 1329.2 685 1042 1565

The differences in the size and shape of the tracks and its number or its track density relative to the etching time would be shown clearly in figure (4-6) below, which include four views of tracks in a detector irradiated with (20 second) and etched at different four etching times (5, 10, 15, 20 minutes).

66

Chapter Four


Figure (4-6) views of CN-85 detector etched chemically at (5, 10, 15, 20 minute) with microwave device. (4-3-2-3) chemically etching with ultrasound device: The irradiated CN-85 track detector with alpha particles at different three doses would be etched chemically for seven times (15, 20, 25, 30, 35, 40, 45 minuet) with use of ultrasound device until reaching the optimum one. The differences in the size and shape of the tracks and its number or its track density relative to the etching time would be shown clearly in figure (4-7) below, this figure shown a picture imaged with optical microscope at 40x magnification, and include four views of the nuclear tracks developed in a detector irradiated with (20 second) and etched at different selected four etching times (15, 25, 35, 45 minutes).

67

Chapter Four


Figure (4-7) four views of CN-85 detector etched chemically at (15, 25, 35, 45 minute) with ultrasound. The utilized etching times and alpha track densities appeared in the detectors, and their averages were listed in the table (4-6). Table (4-6) track densities in CN-85 track detector against different doses and various etching times using ultrasound device. Etching Time Track density (no /mm2) of alpha particles (Min) Time of exposure to alpha source (10 Sec) (20 Sec) (30 Sec) 15 700. 1169 1247 20 703 1225 1349 25 715 1200 1304 30 730 1062 1198 35 746 1080 1084 40 726 913 1151 45 695 868 968 716.4 1073.8 1185.8 Average 746 1225 1349 Max 68

Chapter Four


(4-4) Etching time estimation for CR-39 detector irradiated with neutron emitted from (241Am-Be): CR-39 track detector were be also used to estimate its etching time when irradiated with a stream of thermal neutron emitted from (241AmBe) source, the tracks registries in the detector when irritated a thin pellet of a soil samples sandwiched between two sheets of CR-39 detectors. The heavy nucleus (uranium and thorium) were be fragmented into two large fragments and a number of small fissions, these fissions strike the detectors would originate a nuclear latent tracks in the detector. To develop these tracks we try to etch the detectors chemically with three technique using three devices to see which of them can developed the latent tracks faster, sharply, clearly, and with more density in smaller time. (4-4-1) Chemical etching with water bath: Chemical etching time of the latent tracks originate in CR-39 detector via fission fragments of the heavy nucleus in a five soil samples were be estimated, by select six different etching times at a constant temperature and concentration by the use of water bath. Etching time were be varied staring from the considered one (15minute) till (90minute) with a time interval of 15minute in between in order to investigate the optimum time can be adopted for etching CR-39 detector when detecting fission fragments. The differences in the size of fission tracks and its number or its track density relative to the etching time would be shown clearly in figure (4-8), which includes four views of the tracks developed in a detector and etched at different selected four etching times (15, 45, 60, 90 minutes).

69

Chapter Four


Figure (4-8) four views of CR-39 detector etched chemically at (15, 45, 60, 90) minutes with water bath. The utilized etching times and fission fragments track densities appeared in the detectors, and their averages were listed in the table (4-7). Table (4-7) track densities in CR-39 track detector at different doses and etching times using water bath device. Etching Time Track density (no /mm2) of fission fragments (Min) S1 S2 S3 S4 S5 15 30 45 60 75 90 Average Max

258 619 1169 1178 1062 980 877.6 1178

345 775 788 951 830 786 745.8 951

70

238 862 1360 1681 1483 1027 1108.5 1681

234 512 1405 1852 1731 1452 1197.6 1852

232 833 1525 1832 1721 1416 1259.8 1832

Chapter Four


(4-4-2) chemical etching microwave device: Chemical etching time of the latent tracks originate in CR-39 detector via fission fragments in the five soil samples were be estimated, by choosing six different etching times at constant temperature and concentration by the use of microwave device. Etching time at which the latent tracks started to be developed at a considered amount of tracks staring from (10minute). Four etching times were be selected, starting from (10minute) till (40minute) with a time interval of (10minute) in between, in order to investigate the optimum time can be adopted for etching CR-39 detector when detecting fission fragments. The utilized etching times and fission fragments track densities appeared in the detectors, and their averages and maximum were listed in the table (4-8). Table (4-8) track densities in CR-39 track detector at different doses and etching times using microwave device. Etching Time Track density (no /mm2) of fission fragments (Min) S1 S2 S3 S4 S5 10 20 30 40 Average Max

426.6 550 1247 811.5 758.7 1247

484.7 582.7 962 867.8 724.3 962

479.3 620.9 1109 698.9 727 1109

350 629.9 1216 927.7 780.9 1216

199.7 553.7 1022 974.9 687.5 1022

The differences in size of fission fragments tracks and its number or its track density relative to the etching time would be shown clearly in figure (4-9), which includes four views of the tracks developed in a

71

Chapter Four


detector and etched at different selected four etching times (10, 20, 30, 40 minutes).

Figure (4-9) four views of CN-39 detector etched chemically at (10, 20, 30, 40) minutes with microwave. (4-4-3) chemical etching with ultrasound device: Chemical etching time of the latent tracks originate in CR-39 detector via fission fragments were be estimated, by choosing six different considered etching times at a constant temperature and concentration by the use of microwave device. Latent tracks were start to developed at a considered amounts at (15 minute) etching time, six etching times were be used staring from (15minute) till (90minute) with a time interval of (15 minute), in order to investigate the optimum time can be adopted for etching CR-39 detector when detecting fission fragments. The differences in the size of fission fragments tracks and its number or its track density relative to the etching time would be shown 72

Chapter Four


clearly in figure (4-10), which includes four views of the tracks developed in a detector and etched at different selected four etching times (15, 45, 60, 90 minutes).

Figure (4-10) four views of CR-39 detector etched chemically at (15, 45, 60, 90) minutes with ultrasound. The utilized etching times and fission fragments track densities appeared in the detectors, and their averages and maximum were listed in the table (4-9). Table (4-9) track densities in CR-39 track detector at different doses and etching times using microwave device. Etching Time Track density (no /mm2) of fission fragments (Min) S1 S2 S3 S4 S5 15 329 209 300 105 154 30 1084 559 610 850 1092 45 1440 800 997 1020 1525 60 1562 975 1872 1823 1910 75 1283 780 1351 1644 1713 90 970 541 991 1311 1494 1111.3 644 1020 1125.5 1314.6 Average 1562 975 1872 1823 1910 Max 73

Chapter Four


(4-5) calculations of chemical etching parameters: Five chemical etching parameters of CR-39 and CN-85 detectors when irradiated with alpha particles and fission fragments for the three chemical etching techniques (water bath, microwave and ultrasound) were calculated as follows: a. Bulk etch rate (VB): The bulk etch rate or the etch rate of the undamaged surface is calculated from equation (2-3c), where Dff in this equation (VB= Dff/2t) is the average diameter of the track, which is measured with the use of camera supplied with a software program, by taking the average of several tracks radius measured and then multiplying by two and substituting in the above equation for all our etching times. Tables from (4-10) to (4-19) would be shown the etching time, average of the track diameter at each etching time and the bulk etch rate for all cases as below. Table (4-10) the etching time, average diameter and bulk etch rate for CR-39 detector etched with water bath. Etching Time (t h) Average Track Bulk etch rate (VB) Diameter (D µm) 0.5 1.68 1.680 1 2.43 1.215 1.5 3.29 1.095 2 4.3 1.074 2.5 5.22 1.045 3 6.35 1.058 3.5 7.03 1.005 4 8.21 1.026 1.15 Average

74

Chapter Four


Table (4-11) the etching time, average diameter and bulk etch rate for CR-39 detector etched with microwave. Etching Time (t h) Average Track Bulk etch rate (VB) Diameter (D µm) 0.166 1.82 5.483 0.33 2.50 3.918 0.5 3.33 3.510 0.66 4.2 3.153 Average 4

Table (4-12) the etching time, average diameter and bulk etch rate for CR-39 detector etched with ultrasound. Etching Time (t h) Average Track Bulk etch rate (VB) Diameter (D µm) 0.5 1.67 1.677 1 2.55 1.278 1.5 3.78 1.259 2 4.72 1.180 2.5 5.52 1.104 3 6.7 1.115 3.5 7.57 1.082 4 8.7 1.087 Average 1.22

Table (4-13) the etching time, average diameter and bulk etch rate for CN-85 detector etched with water bath. Etching Time (t h) Average Track Bulk etch rate (VB) Diameter (D µm) 0.25 1.93 3.865 0.33 3.44 5.162 0.41 4.26 5.117 0.5 4.95 4.948 0.583 6.52 5.586 0.66 7.5 5.612 0.75 9.5 6.334 Average 5.23

75

Chapter Four


Table (4-14) the etching time, average diameter and bulk etch rate for CN-85 detector etched with microwave. Etching Time (t h)

Average Track Diameter (D µm) 2.58 3.79 6.39 6.71 Average

Bulk etch rate (VB)

0.0833 0.166 0.25 0.33

15.471 11.359 12.785 10.063 12.42

Table (4-15) the etching time, average diameter and bulk etch rate for CN-85 detector etched with ultrasound. Etching Time (t h)

Average Track Diameter (D µm) 2.544 4.82 6.38 6.62 7.2 7.9 9.7 Average

Bulk etch rate (VB)

0.25 0.33 0.41 0.5 0.583 0.66 0.75

5.089 7.238 7.658 6.620 6.170 5.908 6.470 6.45

Table (4-16) the etching time, average diameter and bulk etch rate for fission fragments in CR-39 detector etched with water bath. Etching Time (t h)

Track Diameter (D µm) 1.47 2.04 2.48 3.11 Average

Bulk etch rate (VB)

0.25 0.5 0.75 1

2.946 2.04 1.650 1.555 2.05

76

Chapter Four


Table (4-17) the etching time, average diameter and bulk etch rate for fission fragments in CR-39 detector etched with microwave. Etching Time (t h)

Average Track Diameter (D µm) 1.5 2.57 2.8 3.51 Average

Bulk etch rate (VB)

0.166 0.333 0.5 0.666

4.420 3.869 2.738 2.632 3.41

Table (4-18) the etching time, average diameter and bulk etch rate for fission fragments in CR-39 detector etched with ultrasound. Etching Time (t h)

Track Diameter (D µm) 1.474 2.041 2.58 3.3 Average

Bulk etch rate (VB)

0.25 0.5 0.75 1

2.946 2.040 1.719 1.644 2.1

b. Track etch rate (VT): Track etch rate or the etch rate along the latent track was calculated from the equation (2-7), where VD which is the diameter rate of the tracks were calculated from the slope of the relation (VD = ΔD/Δt) between track diameters and etching times. Figures from (4-11) to (4-20) represent the slopes for the tables from (4-1) to (4-9).

77

Chapter Four


ΔD (track diametr (µm))

slope= 1.84 µm/h 9 8 7 6 5 4 3 2 1 0 0

1

2

3

4

5

Δt (etching Time (h))

(4-11) slope between track diameter and etching time for CR-39 detector etched with water bath.


slope=6.3 µm/h 4.5 4 3.5 3 2.5 2 1.5 1 0.5 0 0

0.1

0.2

0.3

0.4

0.5

0.6

0.7


(4-12) slope between track diameter and etching time for CR-39 detector etched with laboratory microwave device.

78

Chapter Four



slope=1.925 µm/h 10 9 8 7 6 5 4 3 2 1 0 0

1

2

3

4

5


(4-13) slope between track diameter and etching time for CR-39 detector etched with ultrasound.


slope=13.34 µm/h 10 9 8 7 6 5 4 3 2 1 0 0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8


(4-14) slope between track diameter and etching time for CN-85 detector etched with water bath.

79

Chapter Four

Results and Discussion slope=22.47 µm/h


8 7 6 5 4 3 2 1 0 0

0.05

0.1

0.15

0.2

0.25

0.3

0.35


(4-15) slope between track diameter and etching time for CN-85 detector etched with microwave.

slope=14.32 µm/h ΔD (track diametr (µm))

12 10 8 6 4 2 0 0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8


(4-16) slope between track diameter and etching time for CN-85 detector etched with ultrasound.

80

Chapter Four

Results and Discussion slope=3. 3 µm/h


3.5 3 2.5 2 1.5 1 0.5 0 0

0.2

0.4

0.6

0.8

1

1.2


(4-17) slope between track diameter and etching time for CR-39 detector etched with water bath.

slope=5.477 µm/h ΔD (track diametr (µm))

4 3.5 3 2.5 2 1.5 1 0.5 0 0

0.1

0.2

0.3

0.4

0.5

0.6

0.7


(4-18) slope between track diameter and etching time for CR-39 detector etched with microwave.

81

Chapter Four

Results and Discussion slope=3.438 µm/h


3.5 3 2.5 2 1.5 1 0.5 0 0

0.2

0.4

0.6

0.8

1

1.2


(4-19) slope between track diameter and etching time for CR-39 detector etched with ultrasound. c. Etching rate ratio (V): It's calculated from the equation (2-8), by dividing the average of VT on the average of VB for each case. d. Critical angle of etching (Ɵc): It is determining the appearance of the etched track; it represents the minimum angle at which the etched tracks would appear on the detector surface. There is a certain critical angle for each detector types; it's calculated for all cases from the equation (2-9a). e. Etching efficiency (ƞ): It's the rate between the number of tracks etched in the nuclear track detector to the number of incident particles on it, and it was less than one. It is calculated for all cases from the equation (2-10b). The five etching parameters(VB, VT, V, θC, η) were be listed in three tables; table (4-19), (4-20) and (4-21) which represent the 82

Chapter Four


parameters for; CR-39 and CN-85 detector when irradiated with alpha particles, and when CR-39 detect fission fragments in soil samples at the three using devices (water bath, microwave, ultrasound) respectively as followed: Table (4-19) etching parameters of CR-39 detector irradiated with alpha. Etching device

VB

VT

V

θC

η

Water bath

1.15

2.62

2.278

26.03

0.561

Microwave

4.00

9.5

2.375

24.9

0.58

Ultrasound

1.22

2.87

2.352

25.15

0.575

Table (4-20) etching parameters of CN-85 detector irradiated with alpha. Etching device

VB

VT

V

θC

η

Water bath

5.23

7.13

1.36

47.18

0.267

Microwave

12.42

23.36

1.88

32.11

0.469

Ultrasound

6.45

9.75

1.51

41.41

0.339

Table (4-21) etching parameters of CR-39 detector irradiated with fission fragments in soil samples Etching device

VB

VT

V

θC

η

Water bath

2.05

4.60

2.24

26.46

0.550

Microwave

3.41

7.73

2.26

26.17

0.558

Ultrasound

2.10

4.60

2.19

27.16

0.540

83

Chapter Four


(4-6) Discussion: (4-6-1) Etching time: To discuss the relation between the etching times, track density and doses of irradiation we plot a graphs from (4-19) to (4-28) they are represent tables from (4-1) to (4-9) respectively. (4-6-1-1) Chemically etching of CR-39 detector irradiated with alpha: From the tables (4-1), (4-2) and (4-3) which mention the track density of CR-39 detectors etched chemically at various times with the use of water bath, microwave and ultrasound devices respectively, when the detector was irradiated with different doses. From these tables we can plot the graphs (4-19), (4-20) and (4-21) which showing the following points: 1.

The track density were be Increased with the increasing of the time

irradiation, because the increasing of the alpha radiation dose. 2.

The etching times were being reduced with the increasing of the

radiation dose. 3.

Tracks starting to develop with a Considerable value at (30 minute)

when etching with water bath and ultrasound devices, but with a minimal time (10minute) when etching with microwave because the additional effect of microwave radiation device. 4.

The track density when etching with water bath was increased

between the etching times (60- 150 minute). After that the density begins to decrease because the tracks start to overlap each other's. 5.

For microwave the maximum values of the track density would

appears at etching time range (20-30 minute). 84

Chapter Four 6.


For ultrasound the maximum values of the track density would

appears at etching time between (60- 120 minute). 7.

The average of the track density of the detectors etched with

water bath device is more than the average of the track density of the detectors etched with ultrasound device. 2500

ρ no/mm2

2000 1500 Alpha(10 sec) 1000

Alpha (20 sec) Alpha (30 sec)

500 0 0

30

60

90 120 150 180 210 240 270 Time (min)

Fig (4-20) alpha track density against etching time for (CR-39) detector etched with water bath and irradiated at different doses. 1800 1600

ρ no/mm2

1400 1200 1000

alpha 30 sec

800

alpha 10 sec

600

alpha 20 sec

400 200 0 0

10

20

30

40

50

Time (min)

Figure (4-21) alpha track density against etching time for (CR-39) detector etched with microwave and irradiated at different doses.

85

Chapter Four


2500

ρ no/mm2

2000 1500 alpha (10 sec) 1000

alpha (20 sec) alpha (30 sec)

500 0 0

30

60

90 120 150 180 210 240 270 Time (min)

Figure (4-22) alpha track density against etching time for (CR-39) detector etched with ultrasound and irradiated at different doses.

(4-6-1-2) chemically etching of CN-85 detector irradiated with alpha: From the tables (4-4), (4-5) and (4-6) which mention the track density of CN-85 detectors etched chemically at various times with the use of water bath, microwave and ultrasound devices respectively, when the detector was irradiated with different doses. From these tables we can plot the graphs (4-22), (4-23) and (4-24) which showing the following points: 1.

Increasing the track density with the increasing of the irradiation

time because the raise in the alpha radiation dose. 2.

Reducing the etching time with the increasing of the radiation dose.

3.

Tracks starting to develop with a Considerable value at (15 minute)

when etching with water bath and ultrasound devices, but with a minimal time (5minte) when etching with microwave device because the additional effect of microwave radiation. 86

Chapter Four 4.


For water bath the maximum values of the track density would

appears at etching time between (25 minute - 35 minute) otherwise the track density would decrease because they start to overlap each other's. 5.

For microwave the maximum values of the track density would

appears at etching time between (10- 15 minute) depending upon the dose of irradiation, after this time the track density would decrease because they start to overlap each other's. 6.

For ultrasound the maximum values of the track density would

appears at etching time between (20- 35 minute) depending upon the dose of irradiation, after that the track density would decrease because they start to overlap each other's. 7.

The average of the track density of the detectors etched with water

bath device is more than the average of the track density of the detectors etched with microwave device. 1600 1400

ρ no/mm2

1200 1000 Alpha (10 sec)

800

Alpha (30 sec)

600

Alpha (20 sec) 400 200 0 0

5

10 15 20 25 30 35 40 45 50 Time (min)

Fig (4-23) alpha track density against etching time for (CN-85) detector etched with water bath and irradiated at different doses.

87

Chapter Four


1800 1600

ρ no/mm2

1400 1200 1000

Alpha (10 sec)

800

Alpha (20 sec)

600

Alpha (30 sec)

400 200 0 0

5

10

15

20

25

Time (min)

Fig (4-24) alpha track density against etching time for (CN-85) detector etched with microwave and irradiated at different doses. 1600 1400

ρ no/mm2

1200 1000 800

Alpha (10 sec)

600

Alpha (20 sec)

400

Alpha (30 sec)

200 0 0

5

10 15 20 25 30 35 40 45 50 Time (min)

Fig (4-25) alpha track density against etching time for (CN-85) detector etched with ultrasound and irradiated at different doses. (4-6-1-3) chemically etching of CR-39 detector irradiated with fission fragments: From the tables(4-7), (4-8) and (4-9) which mention the track density of fission fragments in CR-39 detectors etched chemically at various times with the use of water bath, microwave and ultrasound devices respectively, when the detector was irradiated with different 88

Chapter Four


doses. From these tables we can plot the graphs (4-25), (4-26) and (4-27) which showing the following points: 1.

The optimum etching time for all the samples etched with the use

of water bath and ultrasound device would be 60 minutes, after this time the tracks would start to decrease because the small one began to disappear. 2.

The optimum etching time for all the samples etched with the use

of microwave device would be 30 minutes, because after this time the tracks would start to decrease because the small one began to disappear. 3.

The tracks would start to appear at a considerable amount at

(15minute) when etching with water bath or ultrasound devices. 4.

The tracks would start to appear at a considerable amount at (10

minute) when etching with microwave device. 5.

The average of the track density of the detectors etched with water

bath device is more than the average of the track density of the detectors etched with ultrasound device. 2000 1800 1600 ρ no/mm2

1400 1200

S1

1000

S2

800

S3

600

S4

400

S5

200 0 0

15

30

45

60

75

90

105

Time (min)

Fig (4-26) track density of fission fragments against etching time for (CR-39) detector etched with water bath. 89

Chapter Four


1400 1200

ρ no/mm2

1000 S1

800

S2 600

S3

400

S4

200

S5

0 0

10

20

30

40

50

Time (min)

Fig (4-27) track density of fission fragments against etching time for (CR-39) detector etched with microwave.

2500

ρ no/mm2

2000 S1

1500

S2 1000

S3 S4

500

S5

0 0

15

30

45

60

75

90

105

Time (min)

Fig (4-28) track density of fission fragments against etching time for (CR-39) detector etched ultrasound.

90

Chapter Four


(4-6-2) Etching parameters of the track From the tables (4-19), (4-20) and (4-21) we can conclude the following points: a. The etching rate ratio (V) which represent the speed of etching track (VT) relative to the speed of etching surface (VT) have the maximum value when etching in microwave, ultrasound and water bath devices respectively for each CR-39 (alpha and fission detection) and CN-85 detectors, this may be related to the interaction between the microwave radiation and the etching solution during the etching time. b. The critical angle for CR-39 used in detecting alpha particles or fission fragments and CN-85 in detecting alpha has the minimum value when etching with microwave device than the value when etching with water bath or ultrasound devices. This value can be considers the optimum value because the decreasing of this angle leads to increasing the number of the developed tracks. c. The etching (or registration) efficiency of CR-39 detector is much larger than the efficiency of the CN- 85 detector measured for the all same etching devices that are because the CR-39 is more sensitive to alpha particles than CN-85 detector. d. The registration efficiency for the detectors etched with microwave device is greater than that etched with water bath and ultrasound device. The measured efficiency has a good value in comparison with the values obtained from the local studies [35].

91

Chapter Four


(4-7) Conclusions: 1. The etching time will decreased with the increasing of the alpha energy. 2. The track density will increased with the increasing of alpha dose. 3. Latent tracks will be start to develop in all etching devices when their diameters reaching a specific diameter (10 nm). 4. The track density for the detectors etched with water is greater than that etched with microwave or ultrasound respectively. 5. The optimum etching time for CR-39 detector irradiated with alpha particles etched in water bath, microwave and ultrasound would be (60-150 minute), (20- 30 minute) and (60-120 minute) respectively. 6. The optimum etching time for CR-39 detector in fission fragments etched in water bath, microwave and ultrasound would be (45-60 minute) (45- 60 minute) and (20-30 minute) respectively. 7. The optimum etching time for CN-85 detector irradiated with alpha particles etched in water bath, microwave and ultrasound would be (30-35 minute) (10- 15 minute) and (20-35 minute) respectively. 8. The etching efficiency for the detectors etched with microwave is greater than that etched with water bath or ultrasound because their critical angle is less.

92

Chapter Four


(4-8) Future Works: 1. Estimating the etching time at different devices for other nuclear track detectors. 2. Studying the etching parameters with the use of other etching techniques such as plasma and novel room and for other detectors. 3. Study using a microwave device for etching process and estimate the time of etching of the protons.

93

References

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References 11.(IAEA) International Atomic Energy Agency. (Environment Behaviour of Radium Technical Reports Series) Vol. 1, No. 310, P. 192 (1990). 12.Israa Kamel Ahmed Al Rahal, Determination the concentrations and the Transfer Factor for uranium in the Phosphorous Fertilizers from soil to plants by using nuclear track detector (CR-39), the college of science for women-university of Baghdad, (2008). 13.Patty F.A., "Industrial Hygiene and Toxicology". Vol.1, Wiley, New York, p. 45-47, (1958). 14.Malik S.R., "Application of N.IFFDT in studies of Spatial Distribution and Uranium Content". Nuclear Tracks, Vol. 4, p. 309-319, (1981). 15.Khalid Hadi Mahdi Al-Ubaidi, Identification and Measurements of Natural and Industrial Radioactive Pollutants in Environment of Baghdad City Using Gamma Spectrometry and Solid State Nuclear Track Detector CR-39. Ibn Al-Haitham

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Abdulwahab

Concentrations

in

Ridha,

"Determination

Construction

Materials

of

Radionuclides

Used

in

Iraq",

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References biosphere from the Erzgebirge /Sachsen, Germany. Journal of Environmental Radioactivity 64 (2-3): 175-193, (2003). 21.E. B. podgorsak, Radiation physics for medical physicists, (2006). 22.W. E. Meyerhof, Elements of Nuclear Physics, McGraw-Hill, New York, (1967). 23.W. N. Cottingham, D. A. Greenwood, An Introduction to Nuclear Physics, pp 12-13, (2001). 24.Kenneth S. Krane, Introductory Nuclear Physics, New York (1988). 25.Krane, Kenneth S., Introductory Nuclear Physics. John Wiley & Sons. PP. 246–269. (1988). 26.Radford, Edward P.; Hunt, Vilma R., "Polonium-210: A Volatile Radioelement in Cigarettes". Science 143 (3603): 247–249, (1964). 27.James E. Turner, Atoms, radiation, and Radiation protection, (2007). 28.Max H. Lombardi, "Radiation safety in nuclear medicine". Second Edition, (2007). 29.F. A. Smith, A primer in applied radiation physics, queen Mary & wesfield college, London, (2000). 30.A. Das and T. Ferbel. "Introduction to nuclear and particle physics". Second edition, University of Rochester, (2003). 31.Gerhart Friedlander, Joseph W. Kennedy, Edward s. Macias, Julian Malcolm Miller. "Nuclear and Radiochemistry", 3rd Edition, (1981). 32.Tripathy S.P., Kolekar R.V., et al, "Microwave-induced chemical etching (MCE): A fast etching technique for the solid polymeric track detectors (SPTD), September, (2009). 33.H. Saeed Al-Nia’emi, "Effects of Ultrasound in Etching and Detecting Parameters of CR-39 Detector", Department of Physics, 96

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References 70.A.K. Pandey, P.C. Kalsi, R.H. Iyer, Nucl. Instr. And Meth. In Phys. Res. B 134 (1998). 71.M. Toufik, A. Mas, V. Shkinev, A. Nechaev, A. Elharfi, F. Schue´, Eur. Polym. J. 38 (2002). 72.N.M.D. Brown, Z.H. Liu, Appl. Surf. Sci. 93 (1996). 73.Matiullah, S. Rehman, S. Rehman, N. Mati, S. Ahmad, Radiat. Meas. 39 (2005). 74.Torrelles J, Baixeras C, Fernadez . Tracks Rad Meas. 15,183, (1988). 75.S. H. S. Al-Nia'emi and Y. Y. Kasim, Determination of the Bulk Etch Rate of the Nuclear Track Detector CR-39 Using Le-D Method, Jordan Journal of Physics, (2013). 76.A. Waheed and S. Manzoor et. , Nuclear Instruments and Meth, B47 (1990) 320. 77.Shahid Manzoor, Improvements and calibratipon of nuclear track detectors of rare particle searches and fragmentation studies, (2007). 78.Shafi-ur-Rehman, "Radon Measurement with CR-39 Detectors Implications for Uranium Ore Analysis and Risk Assessment", Ph.D. Thesis, Pakistan Institute of Engineering and Applied Sciences, Pakistan, (2005). 79.S. Kodaira, N. Yasuda, N. Hasebe, et al., “Improvement of Mass Resolution for Iron Isotopes in CR-39 Track Detector,” Jpn. J. Appl. Physics, 46, pp. 5281 – 5287 (2007). 80.Al-Rubyie A. Q. M. ," Radioactive Detection On the Blood Samples of Cancer Patients Diseases by using CR-39 Detectors and its Effect on Cytogenetic ", M.Sc. Thesis, Al- Nahrain University, Iraq, (2007).

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References 81.Dazhuang Zhou, "Methods using CR-39 plasstic nuclear track detectors in radiation research", (2010). 82.S. R. Hasshemi – Nezhed, Nucl. Tracks and Rad. meas.Vol. 5, 291, (1982). 83.B.G. Cartwright, E. K. SHIRK and P.B. Price, nucl. Instrum. Methods, 153, 457, (1978). 84.Gartwight B.G.; Shirk E.K. and price P. B. "Nuclear Instruments and Methods", Vol. 153, P 457, (1978). 85.P.C. Kalsi, et al, "Solid State Nuclear Track Detectors and Their Applications’’, (2005). 86.Saaid B. M., "Determination of Radon Concentration in Buildings by using the Nuclear Track Detector CR-39". M.Sc. Thesis, College of Education, Baghdad University, Iraq, (1998). 87.Nichulas T., "Measurement and Detection of Radiation", Pergamon Press, University of Missouri-Rolla, U.K., pp.1-286 (1987). 88.A. Mahmood, H.A. Khawaja, Z. Zahid, M.S. Zafar and M. Tufail, Sci. Int. (Lahore), 6, 5, (1994). 89.H.A. Khan, I. E. Qureshi and M. Tufail, Radiat. Prot. Dosim, 46, 149, (1993). 90.C. Hepburn and A.H windle, J. Mater. sci. 15, 279, (1980). 91.Seaborg, Glenn T. “The Transuranium Elements”. Science 104, 379.(1946). 92.Seaborg, G. T., James, R. A., and Morgan, L. O., "The New Element Americium (Atomic Number 95)," in The Transuranium Elements, New York, (1949). 93.Audi, G; Bersillon, O.; Blachot, J.; Wapstra, A.H. “The evaluation of nuclear and decay properties”. Nuclear Physics A 624. (1997). 94.Strominger, D., Hollander, J. M., and Seaborg, G. T., "Table of Isotopes," Revs. Modern Physics. (1958). 101

References 95.World Nuclear Association. Smoke detectors and americium, (2009). 96.J. E. Strain, G. W. Leddicotte, The preparation, and uses of Americium-241, Alpha, Gamma, and Neutron sources. (1962). 97.I. Kaplen, Nuclear physics, Applid Weslay publishing, (1962). 98.Bonner, T. IJ., Kraus, A. A., Marion, J. B., and Schaffer, J. P., "Neutron Gamma Rays from Alpha-Particle Bombardment of 9Be, 13

C, and 8O,'' Physical Rev. (1956).

99.Binder, Harry H. Lexikon der chemischen Elemente: das Periodensystem in Fakten, Zahlen und Daten: mit 96 Abbildungen und vielen tabellarischen Zusammenstellungen. (1999). 100.

Lakosi L, Nguyen CT, Quantitative NDA of isotopic neutron

sources, Applied Radiation and Isotopes, (2005).

102

‫الخالصة‬ ‫يتضمن هذا البحث دراسة تقنيات مختلفة للقشط الكيميائي للكشف عن المسار النووي‪،‬‬ ‫ومحاولة تقدير الوقت المناسب لقشط االثار الكامنة لجسيمات الفا و شظايا االنشطار الناشئة في‬ ‫اثنين من كواشف االثر النووي للحلة الصلبة (‪ CR-39‬و ‪ )CN-85‬باستخدام الحفر الكيميائي‬ ‫الناجم مع ثالث تقنيات مختلفة؛ حمام الماء‪ ،‬والمايكروويف والموجات فوق الصوتية‪ ،‬من أجل‬ ‫التعرف على تأثير هذه التقنيات واختصار وقت القشط‪.‬‬ ‫وجد ان الوقت النقش األمثل لكاشف ‪ CR-39‬عند التشعيع بجسيمات ألفا القشط في حمام‬ ‫مائي‪ ،‬والمايكرويف والموجات فوق الصوتية (‪ 150-60‬دقيقة)‪ 30 -20( ،‬دقيقة) و (‪120-60‬‬ ‫دقيقة) على التوالي‪ .‬والوقت النقش األمثل لكاشف ‪ CN-85‬عند التشعيع مع جسيمات ألفا‬ ‫المقشوط في حمام مائي‪ ،‬والمايكروويف والموجات فوق الصوتية (‪ 35-30‬دقيقة) (‪15 -10‬‬ ‫دقيقة) و (‪ 35-20‬دقيقة) على التوالي‪ .‬والوقت النقش األمثل لكشف ‪ CR-39‬عند التشعيع بشظايا‬ ‫االنشطار المقشوط في حمام مائي‪ ،‬والموجات الدقيقة والموجات فوق الصوتية (‪ 60-45‬دقيقة)‬ ‫(‪ 60 -45‬دقيقة) و (‪ 30-20‬دقيقة) على التوالي‪.‬‬ ‫حساب المعلمات قشط االثار‪ :‬معدل حفر بالجملة (‪ ،)VB‬ومعدل قشط االثر (‪،)VT‬‬ ‫تقييم نسبة معدل قشط االثر (‪ ،)V‬الزاوية الحرجة (‪ )θc‬والكفاءة القشط (‪.)η‬‬ ‫(أوال) حساب معدل حفر بالجملة (‪ )VB‬عند استخدام ثالث اجهزة (حمام مائي‪،‬‬ ‫الميكروويف والموجات فوق الصوتية) على النحو التالي‪:‬كاشف ‪ CR-39‬المشععة مع جسيمات‬ ‫ألفا كانت النتيجة على التوالي (‪ )1.22 ،4.00 ،1.15‬وكاشف ‪ CN- 85‬المشععة مع جسيمات‬ ‫ألفا كانت النتيجة على التوالي (‪ )6.45 ،12.42 ،5.23‬وكاشف ‪ CR-39‬عن شظايا االنشطار‬ ‫في عينات التربة كانت النتيجة على التوالي (‪.)2.10 ،3.41 ،2.05‬‬ ‫(ثانيا) حساب ومعدل قشط على طول االثر (‪ )VT‬عند استخدام ثالث اجهزة (حمام‬ ‫مائي‪ ،‬الميكروويف والموجات فوق الصوتية) على النحو التالي‪:‬كاشف ‪ CR-39‬المشععة مع‬ ‫جسيمات ألفا كانت النتيجة على التوالي (‪ )2.87 ،9.5 ،2.62‬وكاشف ‪ CN- 85‬المشععة مع‬ ‫جسيمات ألفا كانت النتيجة على التوالي (‪ )9.75 ،23.36 ،7.13‬وكاشف ‪ CR-39‬عن شظايا‬ ‫االنشطار في عينات التربة كانت النتيجة على التوالي (‪.)4.60 ،7.73 ،4.60‬‬

‫(الثالثة) تقييم نسبة معدل قشط االثر (‪ )V‬عند استخدام ثالث اجهزة (حمام مائي‪،‬‬ ‫الميكروويف والموجات فوق الصوتية) على النحو التالي‪:‬كاشف ‪ CR-39‬المشععة مع جسيمات‬ ‫ألفا كانت النتيجة على التوالي (‪ )2.352 ،2.375 ،2.278‬وكاشف ‪ CN- 85‬المشععة مع‬ ‫جسيمات ألفا كانت النتيجة على التوالي (‪ )1.51 ،1.88 ،1.36‬وكاشف ‪ CR-39‬عن شظايا‬ ‫االنشطار في عينات التربة كانت النتيجة على التوالي (‪.)2.19 ،2.26 ،2.24‬‬ ‫(الرابعة) حساب الزاوية الحرجة (‪ )θC‬عند استخدام ثالث اجهزة (حمام مائي‪،‬‬ ‫الميكروويف والموجات فوق الصوتية) على النحو التالي‪:‬كاشف ‪ CR-39‬المشععة مع جسيمات‬ ‫ألفا كانت النتيجة على التوالي (‪ )25.15 ،24.9 ،26.03‬وكاشف ‪ CN- 85‬المشععة مع‬ ‫جسيمات ألفا كانت النتيجة على التوالي (‪ )41.41 ،32.11 ،47.18‬وكاشف ‪ CR-39‬عن‬ ‫شظايا االنشطار في عينات التربة كانت النتيجة على التوالي (‪.)27.16 ،26.17 ،26.46‬‬ ‫(خامسا) حساب الكفاءة القشط (‪ )η‬عند استخدام ثالث اجهزة (حمام مائي‪ ،‬الميكروويف‬ ‫والموجات فوق الصوتية) على النحو التالي‪ :‬كاشف ‪ CR-39‬المشععة مع جسيمات ألفا كانت‬ ‫النتيجة على التوالي (‪ )0.575 ،0.58 ،0.561‬وكاشف ‪ CN- 85‬المشععة مع جسيمات ألفا‬ ‫كانت النتيجة على التوالي (‪ )0.339 ،0.469 ،0.267‬وكاشف ‪ CR-39‬عن شظايا االنشطار‬ ‫في عينات التربة كانت النتيجة على التوالي (‪.)0.540، 0.558،0.550‬‬

‫جمهورية العراق‬ ‫وزارة التعليم العالي والبحث العلمي‬ ‫الجامعة المستنصرية‬ ‫كلية العلوم‬

‫دراسة طرق قشط مختلفة لعدة انواع من كواشف االثر‬ ‫النووي للحالة الصلبة‬ ‫رسالة مقدمة إلى‬ ‫مجلس كلية العلوم – الجامعة المستنصرية‬ ‫وهي جزء من متطلبات نيل درجة ماجستير‬ ‫في علوم الفيزياء‬ ‫من قبل‬

‫ليث عبد الحكيم جبر‬ ‫(بكالوريوس‪)۲۰۱2‬‬ ‫بإشراف‬

‫د‪ .‬ندى فرحان كاظم‬ ‫استاذ مساعد‬ ‫قسم الفيزياء‬

‫‪ ۲۰۱6‬م‬

‫‪۱٤٣7‬هـ‬

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