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Radiation Measurements 36 (2003) 363–366www.elsevier.com/locate/radmeas

Study of uranium, radium and radon exhalation rate in soilsamples from some areas of Kangra district, HimachalPradesh, India using solid-state nuclear track detectors

D.K. Sharma, Ajay Kumar, Mukesh Kumar, Surinder Singh∗

Department of Physics, Guru Nanak Dev University, Amritsar 143 005, India

Received 21 October 2002; received in revised form 26 February 2003; accepted 29 April 2003

Abstract

LR-115 plastic track detectors have been used for the measurement of radon exhalation rate and radium concentration insoil samples collected from some villages of Kangra district, Himachal Pradesh, India. Uranium concentration has also beendetermined in these soil samples using 5ssion track technique. Radium concentration in soil samples has been found to varyfrom 11.54 to 26:71 Bq Kg−1, whereas uranium concentration varies from 0.75 to 2:06 ppm. The radon exhalation rate inthese samples has been found to vary from 15.16 to 35:11 mBq Kg−1 h−1 (502.12 to 1162:64 mBq m−2 h−1).c© 2003 Elsevier Ltd. All rights reserved.

Keywords: Uranium; Radium; Radon exhalation; Track detector

1. Introduction

Uranium, the heaviest radioactive toxic element is foundin almost all types of soils, rocks, sands and water. Uraniumis the ultimate source of 226Ra and 222Rn. Radon isotopes aredecay products of radium in the uranium decay series. Asan inert gas radon can di<use through the soil and enter theatmosphere. Henshaw et al. (1990) has claimed that indoorradon exposure is associated with the risk of leukaemia andcertain other cancers, such as malenoma and cancers of thekidney and prostate. If uranium-rich material lies close to thesurface of earth there can be high radon exposure hazards(Archer et al., 1973; Sevc et al., 1976; UNSCEAR, 1993).Radium is a solid radioactive element under ordinary

conditions of temperature and pressure. It decays to radonemitting �-particles followed by �-radiations. It is the con-centration of radium which governs how many radon atomsare formed. How many of the produced radon atoms leave,i.e. emanate from the mineral grain or matter and enter the

∗ Corresponding author. Tel.: +91-183-225-7007; fax: +91-183-225-8820.

E-mail address: surinder51@yahoo.com (S. Singh).

pore spaces, depends on; where the radium atoms are situ-ated in the grain, the texture and size of the grain, the per-meability of the grains, temperature and pressure (Fleischer,1980, 1982; Tanner, 1980; Anderson et al., 1983). The mea-surements of radon thus necessitate the need for uraniumand radium estimation in the parent source for public healthrisk measurements.

Uranium, radium and radon exhalation studies have beencarried out in Hamirpur, Kullu and Una districts of HimachalPradesh (Kumar et al., 2001; Singh et al., 1998, 2001a, b).In the present investigation, the survey was carried out 5rsttime for the measurements of uranium, radium and radonexhalation rate from some soil samples of Kangra district,Himachal Pradesh.

2. Experimental methods

To understand the migration and exhalation of radon innaturally occurring soils of di<erent areas of district Kan-gra, Himachal Pradesh, India, soil samples were collectedfrom 18 di<erent villages covering an area of approximately60 km2. Geologically district Kangra lies between 31◦40′–32◦25′ east longitudes and 70◦35′–77◦5′ north latitudes.

1350-4487/03/$ - see front matter c© 2003 Elsevier Ltd. All rights reserved.doi:10.1016/S1350-4487(03)00152-5

364 D.K. Sharma et al. / Radiation Measurements 36 (2003) 363–366

The district is bounded on the south-west by Una district; onthe north-west by district Guradaspur of Punjab, on the northby Lahaul-Spiti and Chamba districts, on the east by Kulluand Mandi districts, while on south it touches Hamirpur dis-trict. The elevation generally varies from 500 to 5500 mfrom the mean sea level (Balokhra, 1997). The district iscriss-crossed by mountain ranges (Dhaula Dhar Range) andvalleys.

2.1. Measurements of radon exhalation rate and radiumconcentration

The ‘can technique’ of Abu-Jarad (1988) has been usedfor the measurement of radon exhalation rates in soil sam-ples from 18 di<erent villages of the area. The dried soilsamples from di<erent villages were 5nely powdered andsieved through a 200 mesh seive. The 5ne powder (250 g)of soil sample from each village was placed and sealed indi<erent bottles for 30 days so as to attain the equilibrium.After 1 month, LR-115 type 2 plastic track detectors were5xed on the top inside of these glass bottles (acting as em-anation chambers). The bottles were then sealed and left assuch for 90 days so that the detectors can record �-particlesresulting from the decay of radon. The exposed detectorswere etched in 2:5 N NaOH solution at 60◦C for 2 h usinga constant temperature bath. The tracks were counted usingan optical microscope at 400× magni5cation.

The radon exhalation rate in terms of area is calculatedfrom the equation (Abu-Jarad, 1988; Khan et al., 1992)

EA =CV�

A[T + 1=�(e−�T − 1)]; (1)

where EA is the radon exhalation rate expressed inBq m−2h−1, V is the e<ective volume of the bottle in m3,T is the exposure time in hour (h), � is the decay constantfor radon (h−1) and A is the area of the bottle (m2). Theradon exhalation rate in terms of mass is calculated fromthe expression

EM =CV�

M [T + 1=�(e−�T − 1)]: (2)

Here EM is the radon exhalation rate in terms of mass(Bq kg−1hr−1) and M is the mass of soil sample (250 g).The ‘can technique’ proposed by Alter and Price (1972)

and later developed by Somogyi (1990) has been used tocalculate the radium concentration in soil samples. The ra-dium concentration in soil samples was calculated using therelation

CRadium = hAKTeM

; (3)

where CRadium is the e<ective radium content of soil sample(Bq kg−1), M is the mass of soil sample (250g), A is thearea of cross-section of bottle (7:55 × 10−3 m2), h is thedistance between the detector and the top of the soil sample(0:153 m), K is the sensitivity factor, which is equal to0:0245 tracks cm−2 d−1 per Bq m−3 (Azam et al., 1995)

and Te is the e<ective exposure time which is related withthe actual exposure time T and decay constant � for 222Rnwith the relation

Te = T − 1�(1− e−�T ): (4)

2.2. Uranium estimation

For the estimation of uranium content in soil samples, the5ssion track technique has been used (Azam and Prasad,1989; Jojo, 1993; Singh et al., 2001a, b). A homogeneousmixture was made by taking 50 mg of soil sample powder(200 mesh sieve) from each village and 100 mg of methylcellulose (act as binder and is free from uranium). The smalland thin pellets of soil samples from di<erent villages weremade using a hydraulic pellet making machine. These pel-lets were enclosed in two aluminium capsules after placingthem in-between the Lexan plastic track detector discs andirradiated with thermal neutrons at Bhaba Atomic ResearchCentre Mumbai, India with a thermal neutron dose of about2 × 1015(nvt). The 5ssion fragments resulting from (n, f)reaction in 235U are recorded by Lexan plastic track detec-tors kept in contact with the soil sample and the standardmaterial (Fisher glass).

After etching in 6:25 N NaOH solution at 70◦C for30 min, the developed 5ssion tracks were counted using anoptical microscope at a magni5cation of 400×. Uraniumconcentration was calculated using the relation (Fleischer,et al., 1975)

UX = US

TX

− − −TS

IS

− − −IX

; (5)

where TX and TS represents the 5ssion track density forsample and standard material respectively (Fisher glass, Uconcentration is 20 ppm). IX and IS are the isotopic abun-dance ratios of 235U to 238U in the unknown and standardsamples respectively. IS=IX has been taken as unity assum-ing that the isotopic abundance ratio is same for sample andthe standard (Fleischer et al., 1975).

3. Results and discussion

The values of uranium, radium and radon exhalation ratein soil samples from 18 villages of district Kangra, Hi-machal Pradesh, India are given in Table 1. It is evident fromthe table that the radon exhalation rate in soil varies from502:12 mBq m−2 h−1(15:16 mBq kg−1h−1) in villageHarnota to 1162:64 mBq m−2h−1(35:11 mBq kg−1 h−1)in village Ganoh. The uranium concentration in soil variesfrom 0:75 ppm in village Khajjian to 2:06 ppm in villageNanoohan. The radium concentration in soil varies from11:54 Bq kg−1 in village Harnota to 26:71 Bq kg−1 invillage Ganoh.

D.K. Sharma et al. / Radiation Measurements 36 (2003) 363–366 365

Table 1Values of uranium concentration, radium concentration and radon exhalation rate in soil samples from district Kangra, Himachal Pradesh(India)

Sr. no. Name of the village Uranium conc. (ppm) Radium conc. CRadium (Bq kg−1) Radon exhalation rate

EA (mBq m−2 h−1) EM (mBq kg−1 h−1)

1. Raja Ka Talab 1.43 24.72 1077.11 32.522. Dehri 1.32 22.06 959.89 28.983. Rehan 1.49 15.35 668.44 20.184. Harnota 1.39 11.54 502.12 15.165. Bharmar 0.99 16.93 736.55 22.246. Jawali 1.82 25.72 1119.87 33.827. Pharian 1.63 15.22 662.10 19.998. Batt-Bhalun 1.61 14.10 613.00 18.519. Ganoh 1.46 26.71 1162.64 35.1110. Garan 1.37 17.13 744.47 22.4811. Larath 1.69 18.05 785.65 23.7212. Nanoohan 2.06 18.43 801.49 24.2013. Banal 1.63 16.66 725.46 21.9014. Dhameta 1.15 19.82 861.68 26.0215. Jassur 1.06 21.26 925.04 27.9316. Nurpur 1.43 15.55 676.36 20.4217. Khajjian 0.75 12.53 544.89 16.4518. Dahab 1.15 21.66 942.47 28.46

0

5

10

15

20

25

30

35

40

0 0.5 1 1.5 2 2.5

Rad

on e

xhal

atio

n ra

te (

mB

q K

g-1

h-1)

Uranium conc. (ppm)

Fig. 1. Uranium concentration vs radon exhalation rate in soilsamples.

In the present investigations the observed values of ura-nium concentration in soil are comparable to those deter-mined in the soil of Una district by Kumar et al. (2001)but are lower than those reported in the soil of Hamirpurand Kullu districts of Himachal Pradesh (Singh et al., 1998,2001a, b). The values of radon exhalation rate in soil arequite low as compared with those reported in the soil ofHamirpur district (Singh et al., 1998).

The values of radium concentration in soil observed inthe present investigation are lower than the values deter-mined by Singh (2001) in the soil of Hamirpur district.These values are also less than the permissible value of370 Bq kg−1 (OECD report, 1979) and much lower thanthose reported by Nageswara Rao et al. (1996) and Mittalet al. (1988) for soil of Rajasthan area. The values of ura-nium concentration are also below the recommended safelimit and are not signi5cant from the exploration point ofview. Thus, the results reveal that the area is safe as for as thehealth hazard e<ects of uranium and radium are concerned.The high uranium, radium and radon values in some areasof Hamirpur and Kulu districts may be due to the presenceof uranium mineralization in these areas reported earlier bysome authors (Narayan Dass et al., 1979; Kaul et al., 1993).

Fig. 1 shows a graph between uranium concentration insoil and radon exhalation rate. The graph indicates a positivebut weak correlation between uranium and radon exhalationrate.

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