IOP PUBLISHING JOURNAL OF RADIOLOGICAL PROTECTION

J. Radiol. Prot. 28 (2008) 443–452 doi:10.1088/0952-4746/28/4/R01

REVIEW

Natural radioactivity measurements in Pakistan—anoverview

Said Rahman1, Munazza Faheem1 and Matiullah2,3

1 Pakistan Institute of Engineering and Applied Sciences (PIEAS), PO Nilore, Islamabad, Pakistan2 Physics Division, PINSTECH, Nilore, Islamabad, Pakistan

E-mail: matiullah@pieas.edu.pk and dr matiullah@yahoo.com

Received 19 June 2008, in final form 4 September 2008, accepted forpublication 5 September 2008Published 24 November 2008Online at stacks.iop.org/JRP/28/443

AbstractHumans have always been exposed throughout their period of existenceto naturally occurring ionising radiation. Specifically, naturally occurringradionuclides are present in variable amounts in our environment. Toassess radiological health hazards, naturally occurring radionuclides are beingmeasured in soil, sand, marble, bricks etc throughout the world. In thisregard, extensive data have been reported for Pakistan, which have beencompiled and reviewed in this article. The majority of the reported articlesare about monitoring of the radiological health hazards of naturally occurringradionuclides. In a few articles, use of the radionuclides has been reported forthe exploration of uranium and thorium deposits. Most of the reported datahave been obtained using a high purity germanium detector or a sodium iodidedetector.

1. Introduction

Over the last few decades, there has been an increased concern about public exposuresassociated with the natural radiation environment. The study of the distribution of primordialradionuclides allows an understanding to be developed of the radiological implications ofthese elements due to the γ -ray exposure of the body and irradiation of lung tissue frominhalation of radon and its daughters (Alam et al 1999, Singh et al 2005). The presence ofnatural radioactivity in building materials results in the internal and external exposure of theoccupants. In particular, it is important to assess the radiation hazards arising due to the useof soil, sand and other building materials containing high concentrations of naturally occurringradionuclides in the construction of dwellings. Therefore, assessment of the gamma radiationdose from natural sources is of particular importance, because it is the largest contributor to the

3 Author to whom any correspondence should be addressed.

0952-4746/08/040443+10$30.00 © 2008 IOP Publishing Ltd Printed in the UK

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external dose of the world population (UNSCEAR 1988). The most commonly encounteredprimordial radionuclides are 238U, 232Th, their decay products and 40K. The level of naturalradioactivity in soil and in the surrounding environment, and the associated external exposuredue to the gamma radiation, depends primarily on the geological and geographical conditionsof the region (UNSCEAR 2000). 222Rn is formed through α-decay of 226Ra in the decay chainof 238U, whereas 220Rn, so called thoron, is formed in the decay chain of 232Th. Amongst theradon isotopes, 222Rn is considered to be the most important because of its half-life of 3.8 d(Durrani and Ilic 1997), which is much longer than the half-lives of 220Rn (55.6 s) and 219Rn(4.0 s) (Nazaroff and Nero 1988). When 222Rn decays, the short-lived radon daughters 218Po,214Pb, 214Bi and 214Po are formed.

Under normal circumstances, 40K is the most abundant naturally occurring radioactiveelement within the human body. The average adult male contains about 140 g of potassium(K); but the amount varies with body weight and muscle mass. The daily ingestion rate of K isabout 2.5 g per day and the excretion rate is about the same (Eisenbud and Gesell 1997).

It may be noted here that mass concentrations were converted into activity using thefollowing relationships: 1 ppm of 238U = 12.58 Bq kg−1, 1 ppm of 232Th = 4.07 Bq kg−1 and1% 40K = 296 Bq kg−1 (A Handbook for Exposure Calculations 1995, Radiation assessment2007). The radium equivalent activity (Raeq) was calculated using the following relation(OECD 1979).

Raeq = ARa + 1.43ATh + 0.077AK

where ARa, ATh and AK are the activity concentrations of 226Ra, 232Th and 40K, respectively. Insome of the reported values, error in activity was calculated from the combined uncertainty inthe efficiency of the detector, net count rate and attenuation of the gamma rays by the sample.In some other cases, the error is simply the standard deviation of the reported values and showsthe spread in the measured activity concentrations. Due to increasing social concern, a largenumber of research groups are engaged in the measurement of natural radioactivity at nationallevels worldwide (see for example, Ahmed et al 1997, Matiullah et al 2004, Merdanogluand Altınsoy 2006, Tzortzis et al 2003, Veiga et al 2006, Xinwei 2005). In this regard, anumber of research groups have also been involved in the measurement of natural and artificialradioactivity in Pakistan. However, the reported data are scattered and need to be gathered forfuture reference and planning. A brief review of the work reported so far is presented in thisarticle.

2. Summary of the studies conducted in Pakistan

The research work concerning measurement of natural radioactivity in Pakistan gainedmomentum in the early 1990s and a number of articles appeared in international researchjournals. Tables 1–3 provide a summary of the studies of natural radioactivity conducted inPakistan.

3. Summary of the results

In the above section, the natural radioactivity measurement studies carried out by differentgroups in Pakistan are summarised.

This section deals with results reported by the above-mentioned groups. Tufail et al (1991)reported average activity values in brick samples as 43.3±6.0, 52.2±6.0 and Bq kg−1 for 226Ra,232Th and 40K, respectively. They also estimated a radium equivalent concentration value of169±18 Bq kg−1 in brick samples collected from the Rawalpindi and Islamabad region. Tufailet al (1992a) reported activity concentrations in ceramic materials due to 40K which ranged

Natural radioactivity measurements in Pakistan—an overview 445

Table 1. List of studies conducted using gamma spectrometry of different types of building materialand rock samples.

Materials studied Area of sampling Reference

Brick, ceramic products and cement Rawalpindi and Islamabad/Lahore Tufail et al (1991)Ceramic Lahore Tufail et al (1992a)Cement Pakistan Tufail et al (1992b)Building materials Dera Ismail Khan Tufail et al (1993)Soil, bricks, sand, cement and gravel Islamabad/Rawalpindi and Lahore Tufail et al (1994)

aggregateBrick samples North-West Frontier Province Ali et al (1996)

(NWFP)Miocene–Pliocene rocks Qabool Khel area Qazi and Jafri (1996)Phosphate rock samples/imported Hazara, NWFP Khan et al (1998)

fertiliserCoal samples Punjab and Balochistan Jamil et al (1998)Environmental gamma activity Pakistan Butt et al (1998)Marble samples Salt Range, northern areas and Tufail et al (2000)

BalochistanMarble samples Various geological sites in Pakistan Iqbal et al (2000)Portland cement NWFP Khan and Khan (2001)Marble samples Rawalpindi/Islamabad Aslam et al (2002)Baked brick samples Six highly populated areas of NWFP Khan et al (2002)Rock from Shewa-Shahbaz Garhi NWFP Ali et al (2002)

igneous complexAquatic media North-western areas of Pakistan Khan et al (2003)Fallout radionuclide in environment Islamabad Jabbar et al (2003)Sand North-western areas of Pakistan Khan et al (2005)Soil, vegetation and water NWFP Younis et al (2005)Shallow marine sediments Sindh coast Akram et al (2006a)Phosphate rock/fertiliser Fertiliser samples used in Pakistan Tufail et al (2006a)Inter-tidal sediments Balochistan Coast Akram et al (2007)Branded drinking water Islamabad/Rawalpindi Fatima et al (2007)Brick fabricated from saline soil Lahore and Faisalabad Tufail et al (2007)

from 144 ± 24 to 834 ± 32 Bq kg−1 with an average value of 403 ± 6 Bq kg−1. For 226Ra,they reported activity concentrations which ranged from 63 ± 4 to 124 ± 5 Bq kg−1 with anaverage value of 83 ± 1 Bq kg−1. In the case of 232Th, the activity concentrations varied from10±5 to 125±4 Bq kg−1 with an average value of 86±1 Bq kg−1. They also reported activityconcentrations of natural radionuclides in cement samples (Tufail et al 1992b). They foundthat activity concentrations of 40K varied between 41 ± 34 and 309 ± 33 Bq kg−1. For 226Rathe activity concentrations varied between 18 ± 3 and 60 ± 4 Bq kg−1. The range of activityconcentrations for 232Th was between 16 ± 2 and 51 ± 4 Bq kg−1. Tufail et al (1993) reported226Ra, 232Th and 40K activity concentrations in the dwellings of Dera Ismail Khan as 27, 26and 759 Bq kg−1, respectively. In another article Tufail et al (1994) reported average activityconcentrations of 40K as 758, 214, 107 and 118 Bq kg−1, 226Ra as 49, 36, 27 and 28 Bq kg−1

and 232Th as 63, 285, 13 and 14 Bq kg−1 in brick, cement, aggregate and concrete samplesrespectively.

Qazi and Jafri (1996) reported surface radioactivity in terms of count rate, which rangedfrom 150 ± 25 to 350 ± 25 counts s−1. Uranium contents of 0.16–11.57 ppm (2–146 Bq kg−1)and 0.03–1.25ppm (0.38–16 Bq kg−1) have been reported in animal and plant samples from thearea, respectively.

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Table 2. List of studies for the measurement of natural radioactivity using gamma spectrometry indifferent types of soil samples.

Materials studied Area of sampling Reference

Soil Bahawalpur division Matiullah et al (2004)Virgin and fertilised saline Lahore Akhtar et al (2004a, 2004b)

soils/barren soilSoil Eastern salt range of

PakistanChaudhry et al (2004)

Fertile soil NIAB (Nuclear Institutefor Agriculture andBiology)

Akhtar et al (2004c)

Soil samples Punjab province Tahir et al (2005)Barren and cultivated soil Faisalabad area in the

Punjab province ofPakistan

Tufail et al (2006b)

Soil samples fromagricultural farms

Saline and normal soilwhich had been underfertiliser treatment inLahore/Faisalabad

Akhtar and Tufail (2007)

Soil samples Southern Punjab Fatima et al (2008)Soil samples NWFP Rahman et al (2008)Soil and building material Gujranwala, Gujrat,

Hafizabad, Sialkot,Mandibahauddin andNarowal districts

Faheem et al (2008)

Table 3. List of studies for the measurement of natural radioactivity using different measurementtechniques.

Materials studied Area of sampling Technique used Reference

Building materials Rawalpindi/Islamabad Gamma spectrometry/instrumentalneutron activationanalysis (INAA)

Zaidi et al (1999)

Dietary potassium Pakistani population Atomic absorptionspectrometry

Akhter et al (2003a)

Ingestion of thoriumactivity

Differentdistricts/cities ofPakistan

Instrumental neutronactivation analysis(INAA)

Akhter et al (2003b)

Drinking water Muzaffarabad andhilly areas of Reshian

Fission-tracktechnique

Akram et al (2004)

Sand, stone and otherbuilding materials

Karachi Gamma spectrometryand INAA

Zaidi et al (2004)

Bottom sediments KarachiHarbour/Manorachannel

Gamma spectrometrytechnique/INAA

Akram et al (2006b)

Ore samples Different types ofuranium ore samples

Gamma spectrometrytechnique/inductivelycoupled plasma massspectrometry(ICP-MS)

Rehman et al (2006)

Dietary intakes ofthree naturallyoccurring long-livedradionuclides

Different foodsamples

INAA/ICP-MS/atomicabsorptionspectrometry (AAS)

Akhter et al (2007)

Natural radioactivity measurements in Pakistan—an overview 447

Khan et al (1998) reported very high 226Ra contents in phosphate rock and inlocal/imported fertilisers, which varied from 308 to 618 Bq kg−1. Jamil et al (1998) reportedmaximum activity concentrations for 226Ra, 232Th and 40K as 31±3, 33±3 and 21±5 Bq kg−1,respectively in coal samples collected from the Punjab and Balochistan provinces. Butt et al(1998) reported total gamma activity concentrations for alluvium (shales and clays), sandstone,limestone and shales as 811, 440, 114 and 948 Bq kg−1, respectively. For ultrabasic rocks,basic rocks, granite and metamorphic, intermediate to acidic rocks and metamorphic schistand gneiss, they reported total gamma activity concentrations as 10 Bq kg−1, 240 Bq kg−1,1296 Bq kg−1, 511 Bq kg−1 and 966 Bq kg−1, respectively. Zaidi et al (1999) reportedmean radium equivalent activity concentrations for sand, cement and bricks as 62, 44 and101 Bq kg−1. They also reported 232Th concentrations in samples of bricks, sand and cementthat ranged from 7 to 8 μg g−1 (27–31 Bq kg−1), 4 to 5 μg g−1 (15–21 Bq kg−1) and 2 to4 μg g−1 (7–15 Bq kg−1), respectively.

For 238U, concentration values varied from 2 to 3 μg g−1 (29–34 Bq kg−1), 0.5 to 1 μg g−1

(6–15 Bq kg−1) and 1.2 to 1.7 μg g−1 (15–21 Bq kg−1) in the samples of bricks, sand andcement, respectively, as measured using INAA. In marble samples, Tufail et al (2000) reportedaverage activity concentrations of 27, 26 and 58 Bq kg−1 for 226Ra, 232Th and 40K, respectively.Iqbal et al (2000) reported activity concentrations for marble samples that ranged from 4 to 63,9 to 40 and 7 to 105 Bq kg−1 for 226Ra, 232Th and 40K, respectively.

Khan and Khan (2001) reported a range of combined activity concentrations due to40K, 226Ra and 232Th of 188 ± 64 to 573 ± 73 Bq kg−1 for Portland cement, 55 ± 16to 184 ± 31 Bq kg−1 for limestone, 87 ± 31 to 297 ± 64 Bq kg−1 for gypsum, 696 ± 79to 1044 ± 85 Bq kg−1 for slate and 491 ± 55 to 570 ± 60 Bq kg−1 for latrite. Khan et al (2002)reported average values of the activity concentrations in brick samples due to 40K, 226Ra and232Th as 680±22 to 784±31 Bq kg−1, 37±4 to 52±3 Bq kg−1 and 53±4 to 68±3 Bq kg−1,respectively. Aslam et al (2002) reported activity concentrations of 40K, 226Ra and 232Th inmarble samples that varied from 6 to 160 Bq kg−1, 2 to 29 Bq kg−1 and 1 to 7 Bq kg−1,respectively. Ali et al (2002) reported fairly high mean concentrations of 51 ± 16 Bq kg−1

of 238U, 70 ± 20 Bq kg−1 of 232Th and 1272 ± 367 Bq kg−1 of 40K in samples that werecollected from the quarries and outcrops of the rock units forming the Shewa-Shahbaz Garhiigneous complex, North-West Pakistan.

Khan et al (2003) reported annual ingestion of radionuclides in the aquatic samples,using local consumption rates (averaged over the whole population) of 0.9 l d−1, as 49, 6 and1.1 Bq y−1 for 40K, 226Ra and 232Th, respectively. Akhter et al (2003a) reported the averagedietary potassium concentration as 5 ± 1 mg g−1, which led to a potassium dietary intake of3 ± 1 g/day. For this intake, a daily intake of 40K of 79.94 Bq was reported. They alsoreported thorium concentrations, determined using instrumental neutron activation analysis.The reported values varied from 1.6 ng g−1 (0.0027 Bq kg−1) to 12 ng g−1 (0.054 Bq kg−1)and the median daily thorium intake was 2.7 μg. Matiullah et al (2004) reported the measuredmean activity concentrations in soil samples of 226Ra, 232Th and 40K as 33 ± 1, 54 ± 1 and647 ± 14 Bq kg−1, respectively. The mean radium equivalent activity concentration for thestudied area was reported as 159 ± 4 Bq kg−1.

Akhtar et al (2004a) reported activity concentrations for the naturally occurringradionuclides, namely 40K, 238U and 232Th, in virgin and fertilised saline soil samples.40K for virgin and cultivated saline soil was 500–610.2 Bq kg−1 and 560.2–635.6 Bq kg−1,respectively; 238U, 26.3–31.6 Bq kg−1 and 30.3–38.7 Bq kg−1, and 232Th, 50.6–55.3 Bq kg−1

and 50.6–64.0 Bq kg−1, respectively. Akhtar et al (2004b) also reported the activity of naturalradionuclides as 40K, 524.84–601.62 Bq kg−1, 226Ra, 24.73–28.17 Bq kg−1, and 232Th, 45.46–52.61 Bq kg−1, in the barren soil of Lahore.

448 S Rahman et al

Chaudhry et al (2004) reported average activity concentrations of 40K, 226Ra and 232Thin soil samples as 666 Bq kg−1, 51 Bq kg−1 and 59 Bq kg−1, respectively. Akram et al(2004) reported uranium concentrations in water samples, collected from the Muzaffarabadand Reshian area, which ranged from 0.03 ± 0.01 μg l−1 (0.0004 ± 0.0001 Bq kg−1) to6.67 ± 0.14 μg l−1 (0.084 ± 0.0018 Bq kg−1) with an average value of 1.36 ± 0.05 μg l−1

(0.0170 ± 0.0006 Bq kg−1).Akhtar et al (2004c) also reported activity concentrations of the relevant radionuclides

for the Nuclear Institute for Agriculture and Biology (NIAB) soil as 40K, 614–671 Bq kg−1,226Ra, 29–33 Bq kg−1, and 232Th, 52–60 Bq kg−1. Zaidi et al (2004) reported in samples ofsand, stone and building materials collected from Karachi radium equivalent activities less than370 Bq kg−1. Khan et al (2005) reported activity concentrations of 226Ra, 232Th and 40K insand samples collected from North-West Frontier Province (NWFP) as 37–52, 53–68 and 680–784 Bq kg−1, respectively. Tahir et al (2005) reported mean activity concentrations of 232Th,226Ra and 40K as 41 ± 8, 35 ± 7 and 615 ± 143 Bq kg−1 in soil samples that were collectedfrom different districts of the Punjab. They measured a mean value of the radium equivalentactivity concentration as 141 ± 27 Bq kg−1.

Younis et al (2005) reported average activity concentrations of 40K, 226Ra and 232Th as307 ± 101 Bq kg−1, 10.2 ± 3 Bq kg−1 and 24 ± 6 Bq kg−1, respectively, in soil samples. Theyassessed that vegetation samples had smaller values of activity concentrations and found thatwater samples had concentrations less than the lower limit of detection (LLD), which is 7.44,0.48 and 0.93 Bq for the above-mentioned radionuclides. Akram et al (2006a) reported activityconcentrations in various sediment samples off the Sindh coast, Arabian Sea, which variedfrom 16 ± 5 to 31 ± 5 Bq kg−1 for 226Ra, 12 ± 1 to 34 ± 2 Bq kg−1 for 228Ra and 295 ± 33 to748 ± 29 Bq kg−1 for 40K, respectively. It is noted that 228Ra was measured as a surrogate for232Th, as is common practice.

Tufail et al (2006a) reported activity concentrations of 238U (226Ra) in phosphate rocksamples from Jordan and Pakistan as 428 ± 11 and 799 ± 10 Bq kg−1, respectively. Intriple-superphosphate fertiliser, they reported a mean activity concentration of 238U as 701 ±21 Bq kg−1. They also (Tufail et al 2006b) reported activity concentrations of naturalradionuclides in barren and cultivated soils. For 40K, the values were 499–604 and 563–629 Bq kg−1, respectively; for 226Ra, 24–29 and 27–33 Bq kg−1, and for 232Th, 49–54 and46–62 Bq kg−1. Akram et al (2006b) measured activity concentrations in samples that werecollected from the bottom sediments of the Karachi Harbour/Manora Channel area. Theyreported 226Ra, 228Ra and 40K activity concentrations in sea sediment samples from their studiedarea that varied from 19±4 to 29±4 Bq kg−1 for 226Ra, 12±1 to 28±4 Bq kg−1 for 228Ra and332 ± 9 to 729 ± 37 Bq kg−1 for 40K. They also reported activity concentrations for sedimentsfrom the Layari River which varied from 15 ± 3 to 30 ± 3 Bq kg−1, 9 ± 1 to 32 ± 1 Bq kg−1

and 197 ± 12 to 644 ± 26 Bq kg−1, respectively, for 226Ra, 228Ra and 40K. Rehman et al(2006) calculated 238U concentrations that ranged from 13 to 37 ppm (164–465 Bq kg−1) in oresamples. Radioactivity concentrations measured by Akhtar and Tufail (2007) in soil samplesfrom agricultural farms were from 550–644, 20–35 and 42–58 Bq kg−1 for 40K, 226Ra and232Th, respectively. Akram et al (2007) measured natural radioactivity in various sedimentsamples, which ranged from 14 ± 3 to 37 ± 4 Bq kg−1 for 226Ra, 10 ± 1 to 35 ± 2 Bq kg−1 for228Ra and 145 ± 9 to 611 ± 24 Bq kg−1 for 40K.

Fatima et al (2007) reported mean concentrations of 226Ra, 232Th and 40K in bottleddrinking water as 11 ± 2, 5 ± 0.4 and 141 ± 31 mBq l−1, respectively. In another study, Fatimaet al (2008) reported the mean radium equivalent activity concentration as 96.7±15.2 Bq kg−1

in soil samples from southern Punjab. Tufail et al (2007) reported activity concentrationsof 40K, 226Ra and 232Th in brick samples as 568 ± 38 (493–631), 28 ± 4 (23–35) and

Natural radioactivity measurements in Pakistan—an overview 449

56.0 ± 4.6 (46–65) Bq kg−1, respectively. Akhter et al (2007) reported daily intakes of232Th, 238U and 40K which ranged from 4 mBq to 29 mBq, 17 mBq to 82 mBq and 51 Bq to128 Bq, respectively. Geometric means of the intakes of these radionuclides were 10 mBq d−1,33 mBq d−1 and 78.5 Bq d−1, respectively.

Rahman et al (2008) reported average values of the measured activities of 226Ra, 232Th and40K in soil samples as 26 ± 11, 39 ± 17 and 485 ± 177 Bq kg−1, respectively. The averageradium equivalent activity concentration was found to be 122±42 Bq kg−1 for the studied area.Faheem et al (2008) reported average 226Ra, 232Th and 40K concentrations in soil and buildingmaterial collected from six districts of the Punjab that ranged from 20 ± 9 to 43 ± 17 Bq kg−1,29 ± 8 to 53 ± 9 Bq kg−1 and 98 ± 38 to 621 ± 189 Bq kg−1, respectively. The average radiumequivalent activity concentrations were found to range from 69 ± 25 to 165 ± 32 Bq kg−1.

4. Discussion

In the work reported so far for Pakistan, emphasis has been placed on the health hazardsassociated with the natural radioactivity present in soils and other building materials. Besidesmeasurements of natural radioactivity in soils and building materials, limited data are alsoavailable for Pakistan concerning the use of natural radioactivity in exploration of uraniumand other related mineral deposits in different types of rocks and soil. Few articles regardingmeasurements of natural radioactivity in air have been identified. Most of the studies relatedto natural radioactivity have been conducted using high purity germanium detector (HPGe).However, in several reported studies, a relatively low resolution NaI (Tl) detector has beenused, together with a spectrum stripping technique. A fission-track dating technique has alsobeen used to measure naturally occurring uranium in rocks and water samples. Some researchpapers reported use of the INAA technique for measurement of the gamma ray activity ofradionuclides present in different food and vegetable samples.

The reported values for natural radioactivity show a wide variation in the activityconcentrations of the radionuclides of interest in different types of rocks, soil, sand andbricks. Some studies have also reported the uptake of radionuclides in different types of dietsand bottled mineral water used in Pakistan and have assessed their radiological implications.However, work in this area is scarce and requires further research. Naturally occurringradioactivity has also been reported in the land used for the cultivation of different types ofcrops. However, the area studied represents a very small portion of the cultivated land ofPakistan and, therefore, further research work on this topic would be of much interest.

According to the reported data, natural radioactivity is present in building materials atrelatively low concentrations and is within the permissible limits and thus does not pose aserious threat to the general public. The lowest reported concentrations for 226Ra, 232Th and40K are as 1.45, 1.16 and 7 Bq kg−1, whereas the highest are 799 Bq kg−1, 124 Bq kg−1 and1272 Bq kg−1, respectively. Relatively low activity concentrations of natural radionuclideshave been reported for marble samples, whereas higher values have been reported for phosphaterock samples. The reported range of uranium concentrations in water samples is from 0.03 ±0.01 μg l−1 (0.0004 ± 0.0001 Bq kg−1) to 6.67 ± 0.14 μg l−1 (0.08338 ± 0.0018 Bq kg−1),with an average value of 1.36 ± 0.05 μg l−1 (0.0170 ± 0.0006 Bq kg−1).

5. Conclusions

To conclude, reported data concerning measurements of natural radioactivity in soil, sand,brick, marble and other building materials for Pakistan have been compiled and reviewed inthis article. Reported values show a wide variation of concentrations in different types of

450 S Rahman et al

soil and other building materials. Most of the reported studies used high purity germaniumdetectors (HPGe), whereas in some studies NaI (Tl) detectors together with a spectrumstripping technique and INAA have also been used. High contents of natural radioactivity havebeen reported for phosphate rocks. Therefore, great care needs to be taken using these rocks fordifferent purposes. A fission track dating technique has also been used for the measurement ofuranium contents in different types of rocks. All the reported values of the natural radioactivityin building materials are within permissible limits and do not pose a serious threat to the generalpublic.

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