of Nuclear Research and Development

No.

11

May 2016

J ournal

of Nuclear Research and Development

Journal of Nuclear Research and Development – EDITORIAL COMMITTEE Institute for Nuclear Research (RATEN ICN Pitesti), 115400 Pitesti - Mioveni, str. Campului, no.1, Romania www.jnrd-nuclear.ro [email protected]

Editorial Advisory Board: Clara Anghel (GE-Hitachi Nuclear Energy International LLC, Sweden), Vinicius N.P. Anghel (AECL, Canada), Ioan Viorel Arimescu (AREVA NP INC, US), Kay Birdsell (LANL, US), Ron Cameron (OECD/NEA, France), Mohamad N. H. Comsan (AEA, Egypt), Catalina Oana Curceanu (INFN-LNF, Italy), Dumitru Dobrea (INR Pitesti, Romania), Jean Pierre Van Dorsselaere (IRSN Cadarache, France), Ron Fleck (COG, Canada), Georgios Glinatsis (ENEA Bologna, Italy), Mohamed A. Gomaa (AEA, Egypt), Olena Gritzay (INR Kiev, Ukraine), Viorel Hristea (INR Pitesti, Romania), Dan Ilas (ORNL, US), Germina Ilas (ORNL, US), Bernadette L. Kirk (US), Claire Mays (Symlog Paris, France), Eleodor Nichita (University of Ontario, Institute of Technology, Canada), Dumitru Ohai (Romania), Vasile Radu (INR Pitesti, Romania), Enrico Sartori (France), Bulent Sevdik (Cekmece Nuclear Research and Training Centre, Turkey), Alexandru Toma (INR Pitesti, Romania), Kwok Tsang (AMEC NSS, Canada), George Zyvolovski (LANL, US), Andrew Wallace (Kinectrics, Canada) Production: Alice Dinu, Stefan Preda, Eleonora Dragan, Iuliana Visan Web Edition: Constantin Stoenescu, Alina Constantin Editorial Board: Maria Roth, Minodora Apostol, Daniela Diaconu Editorial General Secretary: Cristina Alice Margeanu Deputy Editor-in-Chief: Daniela Diaconu Editor-in-Chief: Marin Constantin Advisory Group for Editorial Policy: Serban Constantin Valeca, Constantin Paunoiu, Ilie Turcu, Marin Ciocanescu

Journal of Nuclear Research and Development (ISSN 2247 – 191X, ISSN-L = 2247 – 191X) is published by the Institute for Nuclear Research (RATEN ICN) Pitesti, whose Scientific Council has the final responsibility for the Journal. The Advisory Group for Editorial Policy is authorized by INR Pitesti Scientific Council to supervise the Journal editorial policies and practices. The delegated responsibility for overall policy matters concerning JNRD falls under the head of Editor in Chief and Deputy Editor in Chief. The editors of Journal of Nuclear Research and Development are responsible for the scientific content and editorial matters related to the Journal. Copyright © 2016 by the INSTITUTE FOR NUCLEAR RESEARCH, PITESTI, ROMANIA. All rights reserved.

Printed in ROMANIA, PUBLISHING HOUSE of UNIVERSITY of PITESTI, May 2016

CONTENT

Editorial 

″ After Five Years ″ M. Constantin

1



″ Efficiency Evaluation of Nuclear Grade Resins selected for Improvement of the Aqueous Radioactive Waste Treatment Technology ″ M. Dulama, C. Dulama, N. Deneanu

3



″ Comparative Study of Solid Waste Combustion and Microwave Digestion Methods for 14C Measurement by LSC ″ L. Bujoreanu, D. Bujoreanu

8

″ Identification of 235U Short-Lived Fission Products by Delayed Gamma-Ray Emission using Am-Be Neutron Source ″ M. Tohamy, S. Abd El-Ghany, S. M. El-Minyawi, M. Fayez-Hasan, E. H. El-Hakim, S. A. El-Mongy, M. N. H. Comsan

13



″ Sequential Separation of Cs, Ca and Ba for 90Sr Assessment ″ M. Dianu, C. Bucur

19



″ Radiation Shielding Properties of U, Pb, W, Fe, Concrete, Water and Soft Tissues ″ V. P. Singh, N. M. Badiger, M. E-S. Medhat

23



″ Decision Level Fusion od Neutron Backscattering and Microgravity for landmine Detection ″ M. Elkattan, M. Rabei, A. M. Osman

29



″ Estimate of Cesium Transport from Aqueous Radioactive Waste using Emulsions as Carrier ″ C. Arsene, C. Ichim

36



″ Corrosion Behaviour of Dissimilar Welds between Martensitic Stainless Steel and Carbon Steel from Secondary Circuit of CANDU NPP ″ L. Popa, M. Fulger, M. Tunaru, M. Lazar

40



″ Analysis of Incoloy 800HT Alloy tested in Thermal Transient Conditions ″ L. Velciu, T. Meleg, A. Nitu, L. Popa

45



″ Some Aspects of the Social, Societal and Governance Research for Nuclear Energy Development in Romania ″ M. Constantin

50



241

Editorial policy and practices

57

Instructions for authors

59

V.P. SINGH et al.: RADIATION SHIELDING PROPERTIES OF U, PB, W, FE, CONCRETE, WATER AND SOFT TISSUES

RADIATION SHIELDING PROPERTIES OF U, PB, W, FE, CONCRETE, WATER AND SOFT TISSUES VISHWANATH PRATAP SINGH1, NAGAPPA MALLIKARJUN BADIGER1 and MEDHAT EL-SAYED MEDHAT2 1

2

Department of Physics, Karnatak University, Dharwad, India Experimental Physics Dept., Nuclear Research Centre, Atomic Energy Authority, Cairo, Egypt e-mail: [email protected]

Abstract Radiation shielding properties of U, Pb, W, Fe, concrete and soft tissues were studied in terms of mass attenuation coefficients and build-up factors with photon energies. A high atomic number element provides effective gamma ray shielding, therefore shielding properties of these materials have been investigated for energy range 0.015-15 MeV. High atomic number elements provide larger values of mass attenuation coefficients and large build-up factors for high energy photons. However, low atomic number elements containing materials show smaller mass attenuation coefficients and small build-up factors in low- and high-energy photons. The exposure build-up factors of high-Z elements show sharp peak in photoelectric absorption region, which vanishes for intermediate- and low-Z elements. Mixing of high-Z elements with low-Z elements and vice-versa modifies the exposure build-up factors due to alteration in equivalent atomic numbers. Keywords: uranium, soft tissues, build-up factors, gamma, shielding build-up factor at 1.25 MeV, for water, up to 16 mean free paths (mfp). Fano (1953) [2] recognized the significance of build-up factor in shielding studies for multi-energy photon beam with poor geometry. The build-up factor depends on atomic number of elements of the absorbing medium, the photon energy, the penetration depth as well as shape of the radiation source and the medium.

Introduction Gamma exposure of human body occurs in nuclear fuel cycle, nuclear reactors, nuclear installations, accelerators, industries, medical and diagnostic, etc. The gamma exposure is due to production of radiation from fission products of fuel elements and activation products after irradiation. Except medical and industrial application, the gamma source is multi-energetic.

The build-up is defined as the ratio of total value of a specified radiation quantity at any point to the contribution to that value from radiation reaching to the point without having undergone a collision in the passage of radiation through a medium [3]. There are two types of build-up factors, depending on the quantity of interest, namely: (a) the energy absorption build-up factor, in which the interest is for the absorbed or deposited energy in the interacting materials; the detector response function is that of absorption in the interacting medium; (b) the exposure build-up factor (EBF), in which the interest is for the exposure; the detector response function is that of absorption in air.

In nuclear reactors and nuclear fuel cycle, a large spectrum of photon energies is observed. The photon interaction with elements, compounds and composite materials (shielding materials, human organs, dosimetric materials and tissue substitutes, etc) is expressed by effective atomic number (Zeff) and mass attenuation coefficients. The exposure and dose related parameters are being estimated by energy deposition, kinetic energy released per unit mass (kerma) and photon build-up factors. The Zeff signifies the interaction characteristics of a compound or composite material similar to atomic number of a element. The effect of ionizing radiation on human body is characterized by absorbed dose, energy, type of radiation, and the exposed organs.

The shielding materials are being used in reactors, accelerators and other nuclear or radiation facilities for poly-energetic neutral radiation, broad beam and thick shielding materials [4]. Therefore the estimation of buildup factors is extremely important for shielding evaluation and dose assessment.

The transmitted intensity of photon beam through a medium follows Lambert’s Beer law (I=I0e-µt) except for: (i) mono-chromatic beam, (ii) thin absorbing material, and (iii) narrow beam geometry. In case these conditions are met, the law is no longer valid. The law is made valid by using a multiplicative correction factor, called build-up factor, B, whose value is 1 when beam follows Lambert’s Beer law. The concept of build-up factor was introduced by White (1950) [1] by obtaining experimental values of

Goldstein & Wilkins (1954) [5] gave first comprehensive set of gamma-ray build-up factors using moment’s method in six elements (aluminium, tin, iron, tungsten, lead and uranium) and water. 23

JOURNAL OF NUCLEAR RESEARCH AND DEVELOPMENT, NO. 11, MAY 2016 Sakamoto et al. (1988) [6], considering a point isotropic source, used the interpolation technique for computation of build-up factors for 17 elements, water, air, concrete and lead glass, using the G-P fitting method.

studied energy absorption and the exposure build-up factors in some solutions of alkali metal chlorides. Kucuk et al. (2013) [20] modelled gamma-ray energy absorption build-up factors for thermoluminescent dosimetric materials by using multilayer perception neural network.

Simmons (1973) [7] developed the ADJMOM-I code to calculate adjoint moment of flounce at a plane isotropic detector in a finite medium. These energy fluencies moments are then transformed to moments for point isotropic detector by using simple equation. Chilton also studied photon point source build-up factors for air, water and iron. Hirayama et al.(1990) [8] calculated the exposure build-up factors and energy spectra of gammaray in lead for a point isotropic source in the vicinity of Kedge, using PALLAS code [9]. The comparison of PALLAS code with EGS4 [10] and ASFIT codes shows a good agreement.

Tsuruo (1965) [21] has applied a semi-analytic Monte Carlo calculation technique to the duct streaming problem. The statistical deviation of the calculated dose is about 5% for 6000-8000 histories, the relative dose attenuation order being 106. The gamma-rays build-up factors from a point isotropic source for a slab shield are also obtained using this method and results agree with moment’s method. Sardari & Baradaran (2010) [22] and Sardari et al.(2009) [23] computed build-up factors for gamma and X-ray photons, in the energy range of 0.2-2 MeV, in water and soft tissue, using Monte Carlo code (MCNP4C). Kiyani et al.(2013) [24] also used MCNP4C for calculation of buildup factors in depleted uranium, uranium oxide, natural uranium, tin, water and concrete, for the energy range 0.5 to 10 MeV, up to penetration depths from 0.5 to 10 mfp. Deatanyah et al. (2011) [25] determined photon ambient dose build-up factors for radiological applications, considering point and plaque source configurations and using MCNP5 code. Experimental values of build-up factors were found at limited energies (22.16, 24.94, 662 and 1332 keV) for various compounds or mixtures. Buildup factors for some elements and compounds were reported by Martin (2013) [26].

Hirayama & Turbey (1988) [11] studied the effect of incoherent and coherent scattering on the exposure buildup factors for water, iron and lead, in photon energy range 40-200 keV, with penetration depths up to 10 mfp, using Monte Carlo EGS4 code. Hirayama (1995) [12] used EGS4 code for calculation of the exposure build-up factors for water, concrete, iron, and lead, in the photon energy range 10-100 MeV, up to penetration depth of 40 mfp. Using EGS4, Hirayama (1996) [13] has reported the effect of photon cross-section and energy absorption coefficients of air to gamma-ray point isotropic exposure build-up factors for water, iron and lead, in the energy range 0.1 to 10 MeV, with penetration depth up to 40 mfp. Hirayama & Shin (1998) [14] has calculated the multilayer gammaray exposure build-up factors for an isotropic source, up to penetration depth of 40 mfp, by using EGS4 code. Shimizu (2003) [15] has calculated gamma-ray build-up factors for water, iron and lead, at energies of 0.1, 1 and 10 MeV, up to penetration depth of 100 mfp, by using invariant embedding method.

ANSI/ANS-6.4.3 report [27] used the G-P fitting method and provided build-up factor data for 23 elements, water, air and concrete, for standard energies ranging from 0.015 to 15 MeV with suitable interval, up to penetration depth of 40 mfp. Harima reviewed extensively build-up factors and also gave current status for calculation and application for compounds, mixture and elements (Z=4-92). Various researchers have used the G-P fitting method to determine the photon build-up factors for some compound and composite materials [28-33]. This shows that the G-P fitting method is useful for estimating the exposure buildup factors (EBF) of the present materials.

Bakos et al. (1993) [16] performed theoretical calculation and experiments to obtain the transmission dose build-up factors for gamma-rays incident on stratified slabs. The slabs were used in six combinations using aluminium, steel and lead. The build-up factors were determined for two photon energies (1.43 and 2.75 MeV) as a function of mean free path of the slabs.

In the present work, we have investigated theoretically the shielding parameters such as mass attenuation coefficients and exposure build-up factor of U, Pb, W, Fe, concrete and soft tissues. The mass attenuation coefficients and EBF were calculated for photon energy from 0.015 to 15 MeV. The EBF were calculated for penetration depths up to 40 mfp. The results of the present investigation could be useful in the exposure assessment, shielding evaluation and selection of appropriate shielding materials.

Shimizu & Hirayama (2003) [15] developed an improved method for calculation of the gamma-ray build-up factors by including bremsstrahlung radiation. Using this method, exposure build-up factors were calculated for lead, iron and water, at photon energy of 10 MeV, up to penetration depth of 100 mfp. Suteau & Chiron (2005) [17] developed an iterative method for calculation of gamma-ray build-up factors in multi-layer shields. The method is based on an empirical formula for calculating double-layer shield build-up factors. Here neural network approach is being used to provide the equivalent material for a double-layer.

Materials and method In the present investigation, we have considered: elements Uranium, Lead, Tungsten, Iron; composite materials NBS concrete and soft tissue; and water, in order to study their radiation shielding properties such as mass attenuation coefficients and exposure build-up factors. These materials are considered to describe the effect of atomic numbers on shielding properties.

Kurudirek & Özdemir (2011) [18] studied energy absorption and the exposure build-up factors for some polymers and tissue substitute materials, and also their dependency upon the photon energy, penetration depth and chemical composition. Kurudirek & Darius (2013) [19] 24

V.P. SINGH et al.: RADIATION SHIELDING PROPERTIES OF U, PB, W, FE, CONCRETE, WATER AND SOFT TISSUES which depend on the attenuating medium and source energy.

Mass attenuation coefficients The mass attenuation coefficients, µ m =µ ρ (cm2/g) of a compound or composite material is determined by the transmission method, which follows Lambert-Beer’s law. µm for a compound or composite material represents the sum of the (µm)i values of each constituent element, by following mixture rule (= µm

Photon build-up factors from ANSI/ANS-6.4.3 report [27] and those obtained by using G-P fitting method for air, water and lead have been compared in above mentioned references and a good agreement was found. Agreement of present calculations for photon build-up factors with those given in [27] was also good and gives confidence in further calculation of photon build-up factors for various elements, compounds and composite materials.

n

∑ w ( µ / ρ ) ), i

i

where wi is

i

weight fraction and ( µ / ρ )i is mass attenuation coefficient of ith element, using WinXcom developed by Gerward n

(2004) [34]. wi is given by relation wi = ni Ai / ∑ n j Aj with j

Results and discussion The mass attenuation coefficient (µ/ρ) and exposure buildup factor (EBF) of the selected elements, compounds and composite materials are shown in Figures 1 and 2 (a-g), respectively.

n

condition

∑ wi = 1 , where Ai is the atomic weight of the i

ith element and ni is the number of formula units. Exposure build-up factors The compilation for build-up factors was reported in 1991 by American Nuclear Society, ANSI/ANS-6.4.3 [27]. The build-up factor data covers energy range 0.015-15 MeV, up to penetration depth of 40 mfp. The build-up factors given in above mentioned ANS report are for 23 elements (Z=4 to 92). The G-P fitting formula developed by Harima et al.(1986) [35] gives build-up factors in good agreement with those reported by ANSI/ANS-6.4.3. An extensive historical review was reported for photon build-up factors by Harima [3]. Various investigations have been reported for photon build-up factors in different materials.

The µ/ρ and EBF were calculated for photon energy ranging from 0.015 to 15 MeV. Figure 2 (a–g) shows the variation of EBF with photon energy at different penetration depths (up to 40 mfp). Figure 3 shows the exposure build-up factor of UO2. Mass attenuation coefficients Figure 1 shows variation of mass attenuation coefficients (µ/ρ) of selected elements, compounds and composite materials for the photon energy range 0.015 to 15 MeV.

The photon build-up factors and the G-P fitting coefficients are computed by logarithmic interpolation using the equivalent atomic number Zeq of the compound or mixture. The computational work is done in three steps as given below: (1) Calculation of equivalent atomic number; (2) Calculation of G-P fitting coefficients; (3) Calculation of build-up factors. The interactions of photon with matter are through energy and atomic number dependent photoelectric absorption, Compton scattering and pair production. The build-up of photons in the medium is dominated by the Compton scattering, therefore Zeq is calculated from the Compton scattering process. The detailed calculation of Zeq and G-P fitting coefficients is given in references mentioned above.

Fig.1 Mass attenuation coefficients of considered elements, compounds and composite materials The (µ/ρ) values merge in the intermediate energy at around 2 MeV, whereas they have high values in low-as well as high-energy regions. The maximum (µ/ρ) values are observed for uranium, the lowest one being obtained for the soft tissue. When moves towards photoelectric absorption region from Compton scattering, the increasing rate of (µ/ρ) for uranium is the highest and for soft tissue is the lowest due to dependency of the interaction cross section on Z3-4 in photoelectric region. The (µ/ρ) for the materials increases in pair production region and the largest is found for uranium due to dependency of interaction cross section on Z2. Hence, variation of (µ/ρ) can be explained using the partial gamma-ray interaction processes namely, photoelectric absorption, Compton scattering and pair production, where interaction crosssections are dependent upon photon energy and atomic number of elements.

The photon build-up factors are estimated by using G-P fitting coefficients (b, c, a, Xk and d), in the photon energy range of 0.015-15 MeV, up to 40 mfp, according to the formulas given in the following: ( b − 1 )( K x − 1 ) 1+ B( E,x ) = for K ≠ 1 K −1 B( E , x ) =1 + ( b − 1 )x for K =1

(6) (7)

where, for penetration depth (x) ≤ 40 mfp tanh( x / X K − 2 ) − tanh( −2 ) (8) K( E,x= ) cx a + d 1 − tanh( −2 ) where, b is the value of the exposure build-up factor at 1 mfp, x is the source-detector distance for the medium in terms of mfp, K (E, x) is the dose multiplicative factor, and b, c, a, XK and d are the computed G-P fitting coefficients, 25

JOURNAL OF NUCLEAR RESEARCH AND DEVELOPMENT, NO. 11, MAY 2016 Mass attenuation coefficients evolution presented in Figure 1 lead to the observation that uranium is a superior shielding material compared with the other considered materials in the present study.

Exposure build-up factors The variation of exposure buildup factor (EBF) for the selected elements, compounds and composite materials with photon energy is shown in Figures 2 (a-g).

Fig.2 Exposure build-up factors of considered elements, compounds and composite materials 26

V.P. SINGH et al.: RADIATION SHIELDING PROPERTIES OF U, PB, W, FE, CONCRETE, WATER AND SOFT TISSUES It can be observed that variation of EBF with photon energy have a sharp peak for high-Z (Uranium, Lead and Tungsten) and large EBF values at high photon energies. When atomic number of elements reduces, the EBF sharp peak vanishes, whereas large EBF values are still observed at high photon energies. The shift in energy for the EBF peak is observed with reduction of atomic number of element. On the other hand, variation of EBF values of concrete, water, soft tissue shows that EBF values are lower in low- and high- photon energy region compared with those in intermediate photon energy. EBF variation for these compound/composites behaves different from above mentioned elements. The variation of EBF can be explained by partial photon interaction processes. It is also noted that the EBF values of high-Z elements, in high photon energies (~15 MeV), are larger than EBF values in intermediate photon energy for compound/composites.

From Figure 2 (a-g) it can be also noted that the EBF of the materials increases with the penetration depths. The maximum EBF values are due to majority of low-Z elements (H, C and O) in the samples. The EBF decreases with increasing in chemical composition of high-Z elements (see concrete and Iron). From above explanation, it can be noticed that EBF are high for low-as well as high-Z elements or compounds. Therefore, it is very important to choose appropriate material for shielding requirement by considering the photon removal and photon build-up parameters. Effect of mixture of elements on build-up factor In Figs 2 (a-d), variation of the EBF with photon energy is shown for elements. The variation of EBF for mixture of elements is shown in Figures 2 (e-g) and 3.

In low-energy region, photoelectric effect dominates and removes the photons completely. By increasing the photon energy, EBF increases due to dominance of the Compton scattering. In high-energy region (>3MeV), pair/triplet production (removal and generation of photon) takes over the Compton scattering process. This pair production process removes the photon and creates electron and positron pairs. The positron at rest annihilates with electron to generate secondary photon of energy 0.511 MeV. Since in pair production process the interaction cross section is proportional to Z2, large EBF values are observed for high-Z (Uranium, Lead and Tungsten). Sharp peaks in EBF were found at 0.15 MeV, 0.10 MeV and 0.08 MeV for Uranium, Lead and Tungsten, respectively. These sharp peaks in EBF are observed due to K-edge absorption of photon as was similarly shown in Figure 1. In Figure 1 is evident that the K-edge absorption is for Uranium, Lead and Tungsten only, therefore the EBF peaks are observed for same elements. The EBF for water and soft tissue are found similar because the equivalent atomic numbers of both materials are comparable. Also, the EBF values of concrete are found comparable with water and soft tissue because the concrete contain large contribution of low-Z (O: 49%) and minor contribution of higher-Z (Fe: 1.2%).

EBF reaches to 1.5×105 for UO2 which was 3.8×~107 for uranium. However, the EBF for UO2 was found to be 5.3×105, keeping in mind that EBF for uranium element was 4.3×105, at 15 MeV for 40 mfp. This signifies that the mixing of low-Z element with high-Z ones reduces the sharp peak and increases build-up factor for high energies and large penetration depths. It was reported that the EBF values of steel scrap concrete reduce in low- and intermediate-energies, whereas for high energies the EBF values increases with large penetration depths [28].

Conclusions Radiation shielding properties of U, Pb, W, Fe, concrete and soft tissues have been investigated using mass attenuation coefficients and exposure build-up factors.

Mixture of high-Z elements with low-Z elements modifies the exposure build-up factors due to alteration in equivalent atomic numbers.

Fig. 3 Exposure build-up factor of UO2

There is a sharp peak in photoelectric absorption region for exposure build-up factors of high-Z elements and materials; the EBF peak vanishes for intermediate- and low-Z elements.

Therefore, it is very important to choose appropriate material for shielding requirement by considering the mass attenuation coefficients and exposure build-up factors.

References [1] White, G.R. (1950) ″The penetration and diffusion of Co60 gamma-rays in water using spherical geometry″, Phys.

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[2] Fano, U. (1953) ″Gamma-ray attenuation part II-analysis of penetration″, Nucleonics, Vol. 11(9), pg. 5–61

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