Indian Journal of Pure & Applied Physics Vol. 48, July 2010, pp. 493-495
Study of radium and radon exhalation rate in some solid samples using solid state nuclear track detectors B P Singh1, B Pandit1, V N Bhardwaj1, Paramjit Singh2 & Rajesh Kumar2* 1
Department of Chemistry, B S K College, Barharwa, Sahibganj S K M University, Dumka, Jharkhand, India
2
Department of Physics, University School of Basic & Applied Sciences, Guru Gobind Singh, Indraprastha University, Delhi 110 403, India *E-mail:
[email protected] Received 22 April 2010; accepted 20 May 2010
Uranium is a radiotoxic element found in trace quantities in almost all natural occurring materials like soil, rock and sand etc. Radon an inert radioactive gas whose predecessor is uranium, is emitted from soil beneath the house and from building materials. The radium concentration and radon exhalation rates from some solid samples of some area of Santhal Pargana, Jharkhand using LR-115 Type-II plastic track detectors keeping in view the health hazard effects, have been measured. Small strips of LR-115 Type-II film were fitted in bare mode in an emanation chamber for 90 days. The values of radium concentration and radon exhalation rate are found to be maximum in Jamtara district and minimum in Godda district. The values are, generally, found to be more in soil compared with rock and sand samples. Keyword: Radium, Radon exhalation rates, Solid state nuclear track detectors
1 Introduction Radium is a decay product of uranium in the naturally occurring uranium series. When radium decays in soil grains, the resulting atoms of radon isotopes must first escape from the mineral grains to air-filled pores. The rate at which radon escapes or emanates from solid into the surrounding air is known as radon emanation rate or radon exhalation rate of the solid. This may be measured by either per unit mass or per unit surface area of the solid. The fraction of radon formed in the soil grains that escapes into pores is known as the emanation power, coefficient or fraction. The emanation fraction is considered to have two components i.e. recoil and diffusion1,2. The measurement of radon exhalation rates of soil and rocks are helpful to study radon health hazard3-6. Some building materials may be responsible for increased indoor radon levels either due to their higher radon exhalation rates or due to their uranium/radium enrichment as compared to other materials depending on their micro-structure7,8. In the present paper, radium analysis of the samples of soil and rocks belonging to some areas of Santhal Pargana, Jharkhand, has been made. The work has been undertaken keeping in view the health hazard effects of radium in the environment. The radon exhalation rate from these samples is also determined.
2 Experimental Details Some amount of different kinds of rock and soil samples obtained from different location of the region was chosen to understand particularly the migration and exhalation of radon in the naturally occurring rock and soils. The samples were collected in clean and dry polyethylene bags. The collected samples were powdered thoroughly and sieved through a mesh sieve. Radon concentrations in rock and soil have been determined by the Can technique9-11. The technique also known as radon alpha method for radium determination12,13. A glass bottle about one liter in capacity was used as an emanation chamber. A known amount of sample was placed at the bottom of the bottle which was then closed for about one month in order to establish equilibrium between radium, radon members of the decay series. After one month, the mouth of the bottle was opened. LR-115, Type-II plastic track detector in the bare mode was then suspended in side, the bottle at a height such that the direct alpha particles do not reach the detector. The bottle was then closed for 90 days to record alpha activity under equilibrium conditions. After exposure, the detectors were removed and etched in 2.5N NaOH solution at 60°C for 2 h using a constant temperature bath. The tracks were counted using an optical microscope at magnification of 400x.
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The effective radium content of the samples was calculated using the formula: CRa (Bq/kg) =
ρhA KTe M
EM =
where M is the mass of the sample, A the area of cross-section of the cylinder in m2, h the distance between the detector and the tope of solid samples in meters. The effective exposure time was calculated using the equation: Te= T − 1/λ (1−e-λT) where λ is the decay constant for 222Rn, K the sensitivity factor and its value is 0.0245 tracks12 cm−2d−1. The radon exhalation rate in terms of area is obtained from the following14,15:
EA =
also modified to calculate the radon exhalation rate in terms of mass (mBqkg−1h−1):
CV λ A[T + 1 / λ(e −λT − 1)]
where EA is radon exhalation rate in terms of area (Bqm−2h−1); C the intergrated radon exposure as measured by LR-115, Type-II plastic track detector (Bqm−3h); V the effective volume of the Can m−3, λ the decay constant for radon (h−1); T the exposure time (h). A is the area of the Can m2. This formula is
CV λ M [T + 1 / λ (e −λT − 1)]
where EM is radon exhalation rate in terms of mass (mBqkg-1h-1) and M is the mass of the sample. 3 Results and Discussion The result for radium activity and radon exhalation rate in soil, rock and sand samples belonging to some area of Santhal Pargana, Jharkhand, are presented in Tables 1 and 2. The radium activity in soil sample of Jamtara District varies from 19.6- to 15.8 Bqkg−1 whereas in Godda district it varies from 18.4 to 14.3 Bqkg−1, Radon exhalation rate in soil samples in terms of mass of Jamtara district varies from 23.4 to 18.3 mBqkg−1h−1, whereas in Godda District it varies from 22.8 to 17.2 mBqkg−1. The radon exhalation rate in terms of area of Jamtara District varies from from 756.4 to 543.4 mBqm−2h−1 whereas in Godda district it varies from 708.2 to 525.4 mBqm−2h−1. The values of radium concentration and radon exhalation rate are also found to be maximum in Jamtara district and minimum in Godda district. The values are, generally, found to be more in soil samples compared with rock and sand samples. The values of radium activity determined in soil and rocks in, general, are less than
Table 1 — Values of radium and radon exhalation rate in some solid samples of Jamtara district SN
Sample code
Nature of sample
Radium Concen. CRa (Bqkg-1)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Js1 Js2 Js3 Js4 Js5 Js6 Js7 Js8 Js9 Js10 Js11 Js12 Js13 Js14 Js15 Js16 Js17 Js18 Js19 Js20
Soil ” ” ” ” ” ” ” ” ” Rock ” ” ” ” Sand ” ” ” ”
19.6 16.3 17.4 18.2 15.8 17.6 19.1 18.7 16.9 18.5 14.3 13.5 14.6 12.9 12.4 15.6 14.5 13.8 12.7 11.8
Radon exhalation EM (mBqkg-1h-1) EA (mBqm-2h-1) 23.4 19.5 20.2 21.1 18.3 20.7 22.3 21.6 19.8 21.4 17.4 16.2 17.8 15.2 14.8 18.4 17.6 16.2 15.5 15.0
756.4 652.7 672.5 705.8 543.4 688.3 754.5 725.6 653.2 715.8 624.3 590.4 628.5 542.7 515.2 698.3 656.2 603.8 586.7 543.3
SINGH et al.: STUDY OF RADIUM AND RADON EXHALATION RATE IN SOME SOLID SAMPLES
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Table 2 — Values of radium and radon exhalation rate in some solid samples of Godda district SN
Sample code
Nature of sample
Radium concen. CRa (Bqkg−1)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Gs1 Gs2 Gs3 Gs4 Gs5 Gs6 Gs7 Gs8 Gs9 Gs10 Gs11 Gs12 Gs13 Gs14 Gs15 Gs16 Gs17 Gs14 Gs15 Gs16
Soil ” ” ” ” ” ” ” ” ” Rock ” ” ” ” Sand ” ” ” ”
18.2 17.6 16.9 15.6 17.4 15.4 16.5 18.4 15.8 14.3 10.6 11.4 12.7 11.2 10.8 15.4 14.6 13.9 12.2 11.5
the permissible value 370 Bqkg−1, which is acceptable for safe use OECD, 1979. Thus, results reveal that the area is safe as far the health hazard effects are concerned. Acknowledgement The authors also thank University Grants Commission (UGC), New Delhi, for providing financial assistance to carry out this research work. References 1 Tanner A B, A review; The Natural Radiation Environment (University of Chicogo Press) 5, 56, 1964 2 Singh S, Kumar J, Singh B & Singh J, J Rad Meas, 30 (1999) 461. 3 Eaton R S, Proc of workshop on radon and radon daughters in urban communities associated with Uranium mining and processing (Atomic Energy Control Board, Attawa), 1978.
Radon exhalation EM (mBqkg−1h−1) EA (mBqm−2h−1) 21.4 20.3 19.5 18.4 20.1 18.3 19.2 22.8 18.6 17.2 12.5 14.2 16.0 14.1 13.0 18.2 17.4 16.5 15.1 14.3
682.6 633.4 572.8 534.2 618.2 530.5 565.3 708.2 538.6 525.4 506.5 582.3 608.8 569.1 516.6 696.2 667.8 624.3 592.4 540.6
4 Cheng K C & Porrit J M M, CIM BULL: 74 (1981) 110. 5 Khan A J, Prasad R & Tyagi R K, Nucl Tracks Radiat Meas, 20 (1992) 609. 6 Jonsson G, Baixeras C, Devantier R & Treutles H C, Radiat Meas, 31 (1999) 291. 7 Kumar V, Ramachandran T V & Prasad R, Appl Radiat Isot, 51 (1999) 93. 8 Nageswara M V Rao, Bhatti S S, Seshu P & Reddy A R, Radiation Protection Dosimetry, 63 (1996) 207. 9 Somogyi G, Track detection methods of radium measurement, Atomki Pre Print, E/25 (1986) 1-28. 10 Alter H W & Price P B, Patent U S, 3,665,194, 1972, Tarradex Corp USA. 11 Abujarad F, Nucl Tracks Rad Meas, 15 (1988) 525. 12 Azam A, Naqvi A H & Srivastava D S, Nucl Geophys, 9 (1995 ) 653. 13 Singh A K, Jojo P J, Khan A J, Prasad R & Ramachandran T V, Radiat Prot Environ, 3 (1997) 129. 14 Kumar R, Mahur A K, Sengupta D & Prasad R, Radiat Meas 40 (2005) 638. 15 OECD, Nuclear Energy Agency, Paris, France, 1979.
