IOP PUBLISHING JOURNAL OF RADIOLOGICAL PROTECTION

J. Radiol. Prot. 27 (2007) 481–492 doi:10.1088/0952-4746/27/4/009

Natural radioactivity hazards of building bricksfabricated from saline soil of two districts of Pakistan

M Tufail1,3, Nasim-Akhtar2, Sabiha-Javied1,4 and Tehsin Hamid1

1 Pakistan Institute of Engineering and Applied Sciences, PO 45650, Nilore, Islamabad, Pakistan2 Nuclear Institute of Agriculture and Biology, Jhang Road, Faisalabad, Pakistan

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

Received 9 August 2007, in final form 5 November 2007, accepted forpublication 7 November 2007Published 27 November 2007Online at stacks.iop.org/JRP/27/481

AbstractPrimordial radionuclides in building materials are one of the sources of radiationhazard in dwellings made of those materials. Activity concentrations ofprimordial radionuclides 40K, 226Ra and 232Th have been measured in housebuilding bricks fabricated from saline soil. Forty samples of the bricks werecollected from the brick fabrication sites and brick baking kilns in and aroundthe saline soil areas of the districts of Lahore and Faisalabad in the Punjabprovince of Pakistan. The technique of gamma-ray spectroscopy using an HPGedetector with a PC-based multi-channel analyser was applied for determinationof activity concentrations in the brick samples. The activity mass concentrationsof 40K, 226Ra and 232Th measured in the brick samples were respectively567.7±38.3 (493–631), 28.4 ± 3.8 (23–35), and 56.0 ± 4.6 (46–65) Bq kg−1.The radiological hazards of the bricks were calculated using various modelsgiven in the literature. The radium equivalent activity was less than the acceptedstandard criterion value of 370 Bq kg−1 and the values of other hazard indiceswere also below their limit values. The radiological hazard parameters of thebricks under investigation have been compared with those from other locationsof Pakistan and also from some other countries in Asia.

1. Introduction

Radionuclides have been present in the Earth’s crust since it was created. The primordialradionuclides 40K, 226Ra and 232Th are present everywhere in variable amounts [1] and areincorporated in building materials. Indeed, the main source of radiation in building materialsis natural radioactivity [2], and the concentration of primordial radionuclides in such buildingmaterials depends upon the origin of crustal material of which they are composed.

3 Author to whom any correspondence should be addressed.4 Sponsored by HEC, Pakistan.

0952-4746/07/040481+12$30.00 © 2007 IOP Publishing Ltd Printed in the UK

482 M Tufail et al

Naturally occurring radionuclides in building materials are a source of external and internalradiation exposure in dwellings [3]. Human beings in houses are exposed externally to gamma-rays and internally to alpha-, beta- and gamma-rays emitted from radon and its progeny [4–6].The main source of external exposure in dwellings is gamma-rays emitted by the membersof naturally occurring uranium and thorium decay series and by 40K present in constructionmaterials [7]. Natural radioactivity is the largest contributor to the external dose of the worldpopulation [1]; therefore the assessment of gamma radiation dose from natural sources isof particular importance. The dose rate varies depending upon the concentrations of theradionuclides 226Ra (derived from 238U), 232Th, their progeny and 40K, present in buildingmaterials, which in turn depends upon the geological origin of the rock or soil of which thosebuilding materials are composed [8].

The radionuclide content of building bricks used in the Punjab province of Pakistan hasbeen determined in this study. The natural radioactivity in clay bricks has been reported bymany authors [9, 10], and it provides a basis for estimating external exposure in brick-builthouses [11]. Bricks made of soil are the major component of construction materials in thePunjab province of Pakistan. The soil of the region contains clay that consists of fine grains ofless than 4 μm in size and it can be shaped when moist [12]. Bricks are made by compressingthe moist soil into blocks of size 3 × 4 × 9 in3. Almost all the houses in the countryside ofthe Punjab province are made of baked and unbaked compressed soil (clay) bricks. Old housesare made of mud, whereas new construction uses baked and unbaked clay bricks. Except fora few public buildings, almost all the private and public houses in the cities of the Punjabprovince are made of baked clay bricks. Some of the public and commercial buildings areconstructed in column–beam structures in which walls are made of concrete blocks. Thenumber of these buildings may be of the order of 1–2% of the total. Therefore, soil-basedbricks are the dominant component of walls in the houses of the Punjab region.

The present study relates to compressed soil (clay) bricks fabricated from the saline soilareas of the Lahore and Faisalabad districts of Pakistan. Clay bricks used for construction ofhouses in the area are made from the local soil of the area. The soil of the area, being saline,is not very satisfactory for the growing of crops. Most of the area is barren and is covered withunwanted shrubs and trees. However, the soil is suitable for the fabrication of clay bricks. Theshrubs and trees along with coal (peat) are used as fuel in the brick baking kilns. Therefore,a large number of brick fabrication sites and kilns have been developed in the area. Bricksfabricated in the area under study are not only used locally, but are also supplied in variousparts of Pakistan. It is, therefore, important to assess the radiation hazards arising from theseclay bricks due to their extensive use.

For the determination of natural radionuclide concentrations in the environmental samples,various measurement techniques are applied. Gamma-ray activity can be measured withNaI(Tl) and HPGe detectors. The most common technique is the measurement of activityconcentrations with HPGe detectors coupled to a PC-based multi-channel analyser (MCA). Inthis paper, activity concentrations of 40K, 226Ra and 232Th are reported that were measured byHPGe-based gamma-ray spectrometry. Radium equivalent activity and other hazard indiceswere assessed based on accepted specific criteria for the evaluation of the radiological impactof building materials.

2. Experimental methods

2.1. Sample collection and preparation

Twenty samples of clay brick were collected from the saline soil area of Pakka Anna at31◦ 24′ N, 73◦ 05′ E, 34 km south west of Faisalabad city, and 20 samples were collected

Natural radioactivity hazards of building bricks fabricated from saline soil of two districts of Pakistan 483

Figure 1. Map of Pakistan showing the location of the study area.

(This figure is in colour only in the electronic version)

from the Rakh Dera Chal saline area at 30◦ 45′ N, 74◦ 30′ E, 30 km south east of Lahore city inthe Punjab province of Pakistan. The locations of Faisalabad and Lahore are shown in the mapof Pakistan provided as figure 1. The samples were collected from the brick fabrication sitesin saline soil areas around the brick baking kilns. The brick samples were kept in polyethylenebags which were numbered and catalogued for identification. The samples were brought to thesample preparation section of the low-level activity measurement laboratory.

The brick samples were crushed, ground, and pulverised to powder. The powder waspassed through a sieve of 200 mesh size. The samples in powder form were dried at 110 ◦C in atemperature-controlled furnace until there was no detectable change in the mass of the sample.The samples were transferred to radon-impermeable plastic containers of 6 cm diameter and6.5 cm height. The reference material, IAEA Soil 375, was also transferred to a containerof the same material and same dimensions as were used for the soil samples. The samplesand the reference material were stored for more than 40 days to achieve secular equilibriumbetween 226Ra and 222Rn [13]. The samples were shifted, one by one, to the low-level activitymeasurement laboratory of PIEAS for the measurement of activity concentrations.

2.2. Activity measurements

The system employed for the measurement of activity concentration consisted of an HPGedetector coupled to a PC-based MCA of 8196 channels. The detector model was aCANBERRA Ge-3020, having a relative efficiency of 30%, peak to Compton ratio 54,operating voltage 3000 V, placed in a chamber of 30 × 30 × 30 cm3 capacity with 10 cmthick lead shielding having an inner lining of 16 mm copper plus a 5 mm tin graded liner [14].The spectrum of reference Soil 375 was collected for 65 000 s. Background spectra were

484 M Tufail et al

Table 1. Activity concentrations of primordial radionuclides in clay bricks from saline soil areasof Faisalabad and Lahore, Pakistan.

Activity mass concentration (Bq kg−1)

Location 40K 226Ra 232Th

Faisalabad Minimuma 493 ± 22 22 ± 5 46 ± 7Maximuma 631 ± 25 35 ± 6 65 ± 8Meanb 567.7 ± 38.3 28.4 ± 3.8 56.0 ± 4.6

Lahore Minimum 539 ± 24 25 ± 5 43 ± 6Maximum 599 ± 26 31 ± 7 54 ± 7Mean 569.0 ± 17.1 27.2 ± 1.5 48.1 ± 2.8

a The minimum and maximum activity values of the samples with standard errors.b The average value of all the 20 samples with one standard deviation.

collected using empty containers for the same period of time. Background was subtracted fromthe reference soil spectrum. The peak energies of interest in the spectrum have been quotedelsewhere [14]. From the areas under the specific peaks of the spectrum, peak efficiencies weredetermined and plotted as a function of log of efficiency versus log of energy. A polynomial ofdegree three was fitted to the portion of interest in the efficiency curve. The spectrum of eachbrick sample was collected for 65 000 s. Background was collected for two days at weekends.The average of background of two weekends, i.e. 4 days, was subtracted from the brick spectracollected during the week. The activity concentrations of 40K, 226Ra and 232Th were determinedfor every sample.

3. Results and discussion

3.1. Activity mass concentration

The natural radioactivity of clay bricks depends on the origin of clay which, in turn, dependsupon the processes of soil formation. Also, chemical and biological interactions influence thedistribution pattern of uranium and thorium and their decay products in soil [15]. The activitymass concentrations of 226Ra, 232Th and 40K measured in clay brick samples from the salinesoil areas of interest are presented in table 1. The activity concentration ratio 232Th/226Ra wasgreater than unity for all the brick samples under consideration, which is in agreement with theglobal background data on activity concentrations in the Earth’s crust [16, 17]. The averageconcentration of 232Th is about twice that of 226Ra, whereas the concentrations of 40K are muchhigher.

The activity concentrations of 226Ra, 232Th and 40K measured in brick samples fromdifferent locations of Pakistan have been compiled from the literature and are given in table 2.The average of the measured values of the activity concentrations of the radionuclides in thebrick samples of the saline areas of Faisalabad and Lahore are also included in table 2. Theactivity mass concentrations of 40K in the bricks of Faisalabad and Lahore are greater thanthose in the bricks of Jhelum and in some samples from Rawalpindi and Islamabad in thePunjab province, whereas they are smaller than those in all the brick samples of the north westfrontier province (NWFP) of Pakistan.

Average values of concentrations of all the radionuclides under consideration in thebricks of the NWFP and the Punjab province were calculated. The average values for thebrick samples from the NWFP are slightly greater than those from the Punjab province.The deviations from the mean values of the NWFP bricks are relatively smaller than those

Natural radioactivity hazards of building bricks fabricated from saline soil of two districts of Pakistan 485

Table 2. Activity concentrations of primordial radionuclides in clay bricks from some locations ofPakistan.

Activity concentration (Bq kg−1)

LocationNo. ofsamples 40K 226Ra 232Th References

NWFP

Charsada 60 680.3 41.9 67.6 [27]Dera Ismail Khan 90 778.5 51.9 65.2 [27]Dera Ismail Khan 5 791 34 49 [28]Mardan 80 784.4 49.5 64 [27]Nowshera 50 750.3 48.9 62.6 [27]Peshawar 70 753 47.6 60.3 [27]Peshawar + Nowshera + Mardan 21 646 65 84 [29]Risalpur 50 720.6 36.9 52.5 [27]Weighted average 426 745.10 47.66 63.45

Punjab

Dera Ghazi Khan 73 636 50 69 [30]Gujrat 50 591 39 63 [31]Islamabad/Rawalpindi 26 631 43.2 53.7 [32]Islamabad/Rawalpindi 05 335 27 29 [33]Islamabad/Rawalpindi 05 458 29 31 [33]Islamabad/Rawalpindi 05 241 33 33 [33]Jhelum 50 516 39 51 [31]Kasur 25 836.5 54.6 69.6 [34]Lahore 40 790 50 64 [35]Faisalabad (Saline bricks) 20 567.7 28.4 56 Present workLahore (Saline bricks) 20 569.0 27.2 48.1 Present workWeighted average 319 622.57 42.62 59.50

Pakistan

Weighted average 745 692.63 45.50 61.76

of the bricks from the Punjab province. The weighted average values of the radionuclideconcentrations in all the brick samples from both provinces have been determined and areconsidered as representative values for Pakistan. These values are given in tables 2 and 3. Theactivity concentrations of 226Ra and 232Th in the brick samples from Faisalabad and Lahoreare less than the average values for these radionuclides in bricks of the NWFP and the Punjabprovinces.

The data on clay bricks for some of the countries in Asia has been complied from literatureand is represented in table 3 for comparison purposes. There is a great variation in the activityconcentration values of 40K, 226Ra and 232Th measured in the bricks of Asian countries underconsideration. The activity concentration of 40K in the bricks of India is relatively smaller andthat of 226Ra and 232Th in the brick samples of Malaysia are relatively larger than those fromthe other countries.

3.2. Assessment of radiological hazards

The ultimate use of the measured activity concentrations was to assess the radiological hazardsof bricks fabricated from saline soils of the area under consideration. As more than one

486 M Tufail et al

Table 3. Activity concentrations of primordial radionuclides in clay bricks from some countries inAsia together with a world average.

Activity concentration (Bq kg−1)

Location No. of samples 40K 226Ra 232Th References

Bangladesh 10 292.25 29.47 52.5 [36]China 717 41 52 [37]China 20 683.9 68.6 56.4 [38]China (Xi’an) 713.9 58.6 50.4 [39]India (Amritsar) 47.2 12.6 63.7 [40]India (Batala) 48.5 18.1 32.1 [40]India (Batala) 38.7 23.4 14 [40]Iran (Tehran) 45 700 33 30 [41]Kuwait 332 6.6 6.6 [42]Malaysia 3 685 233 229 [43]Sri Lanka 24 585 35 72 [10]Pakistan 745 692.63 45.50 61.76 Present work

World 400 35 30 [1](140–850) (17–60) (11–64)

radionuclide contributes to the radiation dose, it is therefore common practice to present thehazard in terms of a single quantity called a ‘hazard index’. The activity concentrations of226Ra, 232Th and 40K measured in Bq kg−1 are represented by the symbols ARa, ATh andAK, respectively, which occur in the mathematical relations for hazard indices defined in thefollowing sections. Radiological hazard indices have been calculated for the brick samplesfrom the study area, for different locations of Pakistan, and for some counties of Asia, for thepurpose of comparison. If data were available for more than one location in a country, thosedata were averaged and the average value was taken as the representative value for that country.

3.2.1. Radium equivalent activity (Raeq ). Radium equivalent activity is an index that has beenintroduced to represent the specific activities of 226Ra, 232Th and 40K by a single quantity [18],which is calculated through the following relation [19]:

Raeq = 370 ×(

ARa

370+ ATh

259+ AK

4810

)(1)

or

Raeq = ARa + 107 ATh + 10

130 AK.

Radium equivalent activity is the weighted sum of the activities of 226Ra, 232Th and 40K basedon the assumption that 10 Bq kg−1 of 226Ra, 7 Bq kg−1 of 232Th and 130 Bq kg−1 of 40K deliverequal gamma dose rates [20, 21]. From the radiological point of view, the maximum value ofRaeq for a material must be as follows:

Raeq � 370 Bq kg−1.

If Raeq is less than 370 Bq kg−1 then the external dose rate will be below 1.5 mGy y−1 [21, 22].Radium equivalent activity has been calculated for the brick samples under consideration,

and the results are presented in table 4. The values of Raeq ranging from 136.3 to 166.4 Bq kg−1

are less than the maximum admissible value of 370 Bq kg−1 [22]. The external annual dose rate,therefore, does not exceed 1.5 mGy. When the values of Raeq in the clay bricks of Faisalabadand Lahore areas are compared in table 5 with those of other areas of Pakistan, it is observed

Natural radioactivity hazards of building bricks fabricated from saline soil of two districts of Pakistan 487

Table 4. Values of hazard indices for the brick samples of saline areas of Faisalabad and Lahore,Pakistan. (Note: Raeq ≈ radium equivalent activity, Hin ≈ internal hazard index, Iγ ≈ gammaindex, Iα ≈ alpha index.)

Hazard indices

Location Raeq (Bq kg−1) Hin Iγ Iα

Faisalabad Minimum 136.2 0.43 0.51 0.11Maximum 166.3 0.54 0.61 0.18Mean 152.2 0.49 0.56 0.14

Lahore Minimum 132.5 0.42 0.50 0.13Maximum 148.5 0.48 0.55 0.16Mean 139.8 0.45 0.52 0.14

Table 5. Values of hazard indices for bricks from some locations of Pakistan.

Hazard indices

Location Raeq (Bq kg−1) Hin Iγ Iα

NWFP

Charsada 190.8 0.63 0.70 0.21Dera Ismail Khan 204.9 0.69 0.76 0.26Dera Ismail Khan 164.8 0.53 0.62 0.17Mardan 201.3 0.67 0.75 0.25Nowshera 196.0 0.66 0.73 0.24Peshawar 191.7 0.64 0.71 0.24Peshawar + Nowshera + Mardan 234.7 0.81 0.85 0.33Risalpur 167.3 0.55 0.63 0.18Weighted average 195.61 0.65 0.72 0.24

Punjab

Dera Ghazi Khan 197.5 0.67 0.72 0.25Gujrat 174.5 0.57 0.64 0.20Islamabad/Rawalpindi 168.5 0.57 0.62 0.22Islamabad/Rawalpindi 94.2 0.33 0.35 0.14Islamabad/Rawalpindi 108.5 0.37 0.40 0.15Islamabad/Rawalpindi 98.7 0.35 0.36 0.17Jhelum 151.5 0.51 0.56 0.20Kasur 218.4 0.73 0.81 0.27Lahore 202.2 0.68 0.75 0.25Faisalabad (Saline bricks) 152.1 0.49 0.56 0.14Lahore (Saline bricks) 139.7 0.45 0.52 0.14Weighted average 187.00 0.63 0.69 0.23

Pakistan

Weighted average 187.00 0.63 0.69 0.23

that bricks of Faisalabad and Lahore have a larger value of this index than that for some samplesfrom Rawalpindi and Islamabad, but lower values than for other areas of Pakistan.

In the bricks of Asian countries (table 6), the Raeq values range from 41.6 to 612.8 Bq kg−1,respectively, for Kuwait and Malaysia. The values for bricks of Pakistan lie within the worldrange: 43.5–216.8 Bq kg−1. The value of Raeq for the Malaysian bricks is 1.65 times the limit

488 M Tufail et al

50 100 150

Radium equivalent activity (Bq/kg)

0 200

Sri Lanka

Pakistan

Kuwait

Iran

India

China

Co

un

try

World

Bangladesh

Figure 2. Radium equivalent activity concentration of bricks from Pakistan in comparison with thatof the bricks of some other countries in Asia.

Table 6. Values of hazard indices for bricks from some countries of Asia.

Hazard indices

Location Raeq (Bq kg−1) Hin Iγ Iα

Bangladesh 127.0 0.42 0.46 0.15Chinaa 185.91 0.65 0.69 0.28Indiaa 73.77 0.25 0.26 0.09Iran 129.7 0.44 0.49 0.17Kuwait 41.6 0.13 0.17 0.03Malaysia 612.8 2.28 2.15 1.17Pakistan 187.0 0.63 0.69 0.23Sri Lanka 182.9 0.59 0.67 0.18

World 108.6 0.39 0.40 0.18(43.5–216.8) (0.16–0.74) (0.16–0.80) (0.09–0.30)

a Mean of the values calculated for the bricks from the locations given in table 3.

of 370 Bq kg−1. The population of Malaysia, according to the given data, is at significant riskof external radiation in a room made of Malaysian clay bricks. For comparison purposes, Raeq

for the countries of Asia under consideration except Malaysia are shown graphically in figure 2.The values of Raeq of the bricks of China, Pakistan and Sri Lanka are almost equal, but greaterthan those of other countries in comparison.

3.2.2. External hazard index (Hex). The external hazard index is another criterion to assessthe radiological suitability of a building material. It is defined as follows [19]:

Hex = ARa

370+ ATh

259+ AK

4810. (2)

To limit the external gamma radiation dose from building materials to 1.5 mGy y−1 the externalhazard index, Hex, should obey the following relation [22]:

Hex � 1.

The external hazard index is obtained from the expression for Raeq through the suppositionthat its maximum allowed value (equal to unity) corresponds to the upper limit of Raeq

Natural radioactivity hazards of building bricks fabricated from saline soil of two districts of Pakistan 489

(370 Bq kg−1) so that the annual external dose rate does not exceed 1.5 mGy. The behaviourof Hex is similar to that of Raeq, because Hex = Raeq/370; therefore it has not been furtherdiscussed.

3.2.3. Internal hazards index (Hin). The internal hazard index is a criterion for indoorradiation hazard. In addition to gamma-rays, 222Rn plays an important role for internal exposurein a room. Effectively, the radiotoxicity of 226Ra is increased by a factor of two to allow for thecontribution from 222Rn and its short-lived progeny. The internal exposure due to radon andits daughter products is quantified by the internal hazard index, Hin, which has been defined asshown below [19]:

Hin = ARa

185+ ATh

259+ AK

4810. (3)

The internal hazard index is defined so as to reduce the acceptable maximum concentration of226Ra to half the value appropriate to external exposure alone. For the safe use of a material inthe construction of dwellings the following criterion was proposed by Krieger [22]:

Hin � 1.

Using equation (3), internal hazard indices were calculated for the brick samples fromFaisalabad and Lahore. The calculated values of Hin range from 0.43 to 0.54, as given in table 4.The values of Hin for bricks from other areas of Pakistan have been derived from the data givenin table 2 using equation (3), and are given in table 5. The bricks from Faisalabad and Lahorehave larger values of Hin than those of some samples from Rawalpindi and Islamabad, but lessthan the average values of this index for the bricks of the NWFP and the Punjab province ofPakistan. Values of Hin were also calculated for the bricks of some countries of Asia, and thesevalues are given in table 6. The value of this index is less than unity for bricks of all countries ofinterest, except for bricks from Malaysia. The value of Hin for Pakistani bricks is 0.63, whichlies within the world range of 0.16–0.74.

3.2.4. Gamma index (Iγ ). Another radiation hazard index, called the gamma activityconcentration index, Iγ , has been defined by the European Commission [23, 24] and is givenas below:

Iγ = ARa

300+ ATh

200+ AK

3000. (4)

The index Iγ is correlated with the annual dose rate due to the excess external gamma radiationcaused by superficial material. Values of index Iγ � 2 correspond to a dose rate criterion of0.3 mSv y−1, whereas 2 < Iγ � 6 corresponds to a criterion of 1 mSv y−1 [23, 25]. Thus, theactivity concentration index should be used only as a screening tool for identifying materialsthat might be of concern to be used as construction materials; though material with Iγ > 6should be avoided, since these values corresponds to dose rates higher than 1 mSv y−1 [23],which is the highest value of dose rate recommended for population [1]. The EuropeanCommission (EC) suggests that building materials should be exempted from all restrictionsconcerning their radioactivity provided the excess gamma radiation originating from them doesnot increase the annual effective dose to a member of the public by more than 0.3 mSv [24].Dose rates higher than 1 mSv y−1 should be permitted only in some very exceptional caseswhere materials are used locally.

The index Iγ was estimated using equation (4). The distribution of values of the indexIγ for the bricks analysed in this work is presented in table 4. Bricks are used in bulk forconstruction of houses in the Punjab province of Pakistan. The gamma index Iγ for such bricks

490 M Tufail et al

ranges from 0.51 to 0.61, which lies within the acceptable range of up to 1.0 for material used inbulk amounts. All the values of Iγ are <2.0. Therefore, the annual effective dose delivered bybuildings made of such bricks is smaller than the annual effective dose constraint of 0.3 mSv;hence the bricks can be exempted from all the restrictions concerning radioactivity. The averagevalue of this index for the bricks of Faisalabad and Lahore is less than the average value of Iγfor the bricks of the NWFP and the Punjab provinces. The gamma dose rates from the bricksfrom the two provinces of Pakistan given in table 5 are smaller than the general public doseconstraint of 0.3 mSv y−1. The Iγ value of Pakistani bricks given in table 6 is 0.70, which lieswithin the world range 0.16–0.80 but is larger than the world average value of 0.40.

3.2.5. Alpha index (Iα). The excess alpha radiation due to radon inhalation originating frombuilding materials is assessed through the alpha index, which is defined as follows [24]:

Iα = ARa

200. (5)

The recommended exemption level and recommended upper level of 226Ra activityconcentrations are 100 Bq kg−1 and 200 Bq kg−1, respectively, in building materials assuggested in many countries of the world [26]. When the 226Ra activity concentration ofa building material exceeds the value of 200 Bq kg−1, it is possible that radon exhalationfrom this material could cause indoor radon concentrations exceeding 200 Bq m−3. Onthe other hand, when the 226Ra activity concentration is below 100 Bq kg−1, then radonexhalation from the building materials could not cause indoor radon concentrations exceeding200 Bq m−3 [26]. These considerations are reflected in the alpha index. The recommendedupper limit concentration of 226Ra is 200 Bq kg−1, for which Iα = 1.

As can be observed from table 1, the activity concentration values of 226Ra in all thebrick samples are less than the recommended exemption level of 100 Bq kg−1 and Iα < 0.5.Therefore, radon inhalation from the brick samples under investigation is not so large as torestrict the use of these bricks in construction. This is also true for all the brick samples fromvarious locations in Pakistan and some of the Asian countries under consideration.

4. Conclusions

Activity mass concentrations of 40K, 226Ra and 232Th in bricks made of saline soil of Faisalabadand Lahore districts have been measured using the technique of gamma-ray spectrometry withan HPGe detector. The concentrations are similar to those of other locations of Pakistan, butdiffer from those from other Asian countries under consideration. The activity concentrationvalues of 40K, 226Ra and 232Th for the bricks of Kuwait and Malaysia are at the lowest and thehighest extremes, respectively. The values of hazard indices derived from the measured activityconcentrations of primordial radionuclides in the brick samples from the areas under study arebelow the permissible limiting values. The value of Hex < 1; therefore, Raeq < 370 Bq kg−1

and annual gamma doses in rooms made of such bricks are less than 1.5 mGy. Since Hin < 1and Iα < 0.5, rooms made from bricks of the area under study should not pose a significantproblem of radon. The values of hazard indices for bricks from China, Pakistan and Sri Lankaare comparable but larger than those from other countries in the region, except for Malaysia,which has exceptionally high values of these indices. The values of radiological parameters forIndian bricks are about half of the world average values. The behaviour of other hazard indicesis similar to that of Raeq.

Natural radioactivity hazards of building bricks fabricated from saline soil of two districts of Pakistan 491

Acknowledgments

One of the authors, Sabiha-Javied, acknowledges the Higher Education Commission (HEC) ofPakistan and appreciates its financial support through ‘Indigenous Scholarship Scheme for PhDstudies in Science and Technology’.

References

[1] United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) 2000 Sources and effectsof ionizing radiation. Volume I: Sources Report to the General Assembly, with Scientific Annexes

[2] Ngachin M, Garavaglia M, Giovani C, Kwato Njock M G and Nourreddine A 2007 Assessment of naturalradioactivity and associated radiation hazards in some Cameroonian building materials Radiat. Meas. 42 61–7

[3] Amrani D and Tahtat M 2001 Natural radioactivity in Algerian building materials Appl. Radiat. Isot. 54 687–9[4] Organo C and Murphy P 2007 The Castleisland radon survey- follow-up to the discovery of a house with

extremely high radon concentrations in County Kerry (SW Ireland) J. Radiol. Prot. 27 275–85[5] Labidi S, Essafi F and Mahjoubi H 2006 Estimation of the radiological risk related to the presence of radon 222

in a hydrotherapy centre in Tunisia J. Radiol. Prot. 26 309–16[6] Miles J C H and Appleton J D 2005 Mapping variation in radon potential both between and within geological

units J. Radiol. Prot. 25 257–76[7] Malanca A, Pessina V, Dallara G, Luce C N and Gaidolfi L 1995 Natural radioactivity in building materials from

the Brazilian state of Espı́rito Santo Appl. Radiat. Isot. 46 1387–92[8] Mirza N M, Ali B, Mirza S M, Tufail M and Ahmad N 1991 A shape and mesh adaptive computational

methodology for gamma ray dose from volumetric sources Radiat. Prot. Dosim. 38 307–14[9] El-Tahawy M S and Higgy R H 1995 Natural radioactivity in different types of bricks fabricated and used in the

Cairo region Appl. Radiat. Isot. 46 1401–6[10] Hewamanna R, Sumithrarachchi C S, Mahawatte P, Nanayakkara H L C and Ratnayake H C 2001 Natural

radioactivity and gamma dose from Sri Lankan clay bricks used in building construction Appl. Radiat. Isot.54 365–9

[11] Organization of Economic Cooperation and Development (OECD) 1979 Exposure to radiation from naturalradioactivity in building materials Report by a Group of Experts of the OECD (Paris: Nuclear Energy Agency)

[12] Parteous A 2000 Dictionary of Environmental Science and Technology 3rd edn (Chichester: Wiley)[13] Tufail M, Nasim-Akhtar and Waqas M 2006 Radioactive rock phosphate: the feed stock of phosphate fertilizers

used in Pakistan Health Phys. 90 361–70[14] Akhtar N, Tufail M, Ashraf M and Mohsin Iqbal M 2005 Measurement of environmental radioactivity for

estimation of radiation exposure from saline soil of Lahore, Pakistan Radiat. Meas. 39 11–4[15] El-Taher A and Uosif M A M 2006 The assessment of the radiation hazard indices due to uranium and thorium

in some Egyptian environmental matrices J. Phys. D: Appl. Phys. 39 4516–21[16] Tufail M, Nasim-Akhtar and Waqas M 2006 Measurement of terrestrial radiation for assessment of gamma dose

from cultivated and barren saline soils of Faisalabad in Pakistan Radiat. Meas. 41 443–51[17] Schmus W R V 1995 Natural radioactivity of crust and mantle Global Earth Physics: A Handbook of Physical

Constants ed T J Ahrens (Washington, DC: American Geophysical Union)[18] Hamilton E I 1971 The relative radioactivity of building materials Am. Ind. Hyg. Assoc. J. 32 398–403[19] Beretka J and Matthew P J 1985 Natural radioactivity of Australian building materials, industrial wastes and

by-products Health Phys. 48 87–95[20] Stranden E 1976 Some aspects on radioactivity of building materials Phys. Norv. 8 167[21] Krisiuk E M, Tarasov S I, Shamov V P, Shlak N I, Lisachenko E P and Gomelsky L G 1971 A Study of

Radioactivity in Building Materials (Leningrad: Research Institute for Radiation Hygiene)[22] Krieger R 1981 Radioactivity of construction materials Betonwerk Fertigteil-Tech. 47 468[23] European Commission (EC) 1999 Radiation Protection 112—radiological protection principles concerning

the natural radioactivity of building materials Directorate-General Environment, Nuclear Safety and CivilProtection

[24] Righi S and Bruzzi L 2006 Natural radioactivity and radon exhalation in building materials used in Italiandwellings J. Environ. Radioact. 88 158–70

[25] Anjos R M et al 2005 Natural radionuclide distribution in Brazilian commercial granites Radiat. Meas.39 245–53

[26] The Radiation Protection Authorities in Denmark, Finland, Iceland, Norway and Sweden 2000 NaturallyOccurring Radiation in the Nordic Countries—Recommendations The Flag-Book Series (Reykjavik)

492 M Tufail et al

[27] Khan K, Aslam M, Orfi S D and Khan H M 2002 Norm and associated radiation hazards in bricks fabricated invarious locations of the North West Frontier Province (Pakistan) J. Environ. Radioact. 58 59–66

[28] Khan E U, Tufail M, Ahmad N, Malik Q N, Amjad M and Zulqarnain S M Q 1995 Natural radioactivity frombuilding materials used in Dera Ismail Khan, Pakistan Turkish J. Nucl. Sci. 22 37–47

[29] Ali S, Tufail M, Jamil K, Ahmad A and Khan H A 1996 Gamma ray activity and dose rate of brick samples fromareas of the North West Frontier Province (NWFP), Pakistan Sci. Total Environ. 187 247–52

[30] Mahmood A, Ashiq M, Hussain T and Tufail M 1996 Natural radioactivity in bricks and sand samples of DeraGhazi Khan, Pakistan The Nucleus 33 75–8

[31] Tufail M, Zafar M S, Ahmad Z and Hussain S 1993 Gamma activity in the soil used for fabrication of bricks inGujrat and Jhelum districts of Pakistan Proc. 2nd All Pak. Sci. Conf. (Aitcheson College, Lahore, Dec. 1993)

[32] Tufail M, Ahmad N, Khan H A and Zafar M S 1991 Gamma activity in the bricks used for the construction ofdwellings in Rawalpindi and Islamabad areas of Pakistan Radiat. Prot. Dosim. 37 197–200

[33] Zaidi J H, Arif M, Ahmad S, Fatima I and Qureshi I H 1999 Determination of natural radioactivity in buildingmaterials used in the Rawalpindi/Islamabad area by γ -ray spectrometry and instrumental neutron activationanalysis Appl. Radiat. Isot. 51 559–64

[34] Tufail M, Sarwar M S, Almakky S, Mirza S M, Ahmad N, Zafar F I and Zafar M S 1991 Natural radioactivity inthe bricks fabricated around Kasur (Pakistan) Sci. Int. (Lahore) 3 15–8

[35] Tufail M, Ahmad N, Zafar M S, Siddiqui M S, Sarwar M S, Ali S and Almakky S 1993 Gamma activity inLahore: Pakistani building materials Arab. J. Sci. Eng. 18 353–63

[36] Chowdhury M I, Alam M N and Ahmed A K S 1998 Concentration of radionuclides in building and ceramicmaterials of Bangladesh and evaluation of radiation hazard J. Radioanal. Nucl. Chem. 231 117–22

[37] Ziqiang P, Yin Y and Mingqiang G 1988 Natural radiation and radioactivity in China Radiat. Prot. Dosim.24 29–38

[38] Xinwei L 2004 Natural radioactivity in some building materials and by-products of Shaanxi, China J. Radioanal.Nucl. Chem. 262 775–7

[39] Xinwei L 2005 Natural radioactivity in some building materials of Xi’an, China Radiat. Meas. 40 94–7[40] Kumar A, Kumar M, Singh B and Singh S 2003 Natural activities of 238U, 232Th and 40K in some Indian building

materials Radiat. Meas. 36 465–9[41] Fathivand A A, Amidi J and Najafi A 2007 The natural radioactivity in the bricks used for the construction of the

dwelling in Tehran areas of Iran Radiat. Prot. Dosim. 123 391–3[42] Bou-Rabee F and Bem H 1996 Natural radioactivity in building materials utilized in the state of Kuwait

J. Radioanal. Nucl. Chem. Lett. 213 143–9[43] Chong C S and Ahmad G U 1982 Gamma activity of some building materials in West Malaysia Health Phys.

43 272–3