Determination of natural radioactivity and associated radiation hazardin building materials used in Weinan, China

Xinwei Lu n, Shigang Chao, Fang YangSchool of Tourism and Environment, Shaanxi Normal University, Xi’an 710062, People's Republic of China

H I G H L I G H T S

� We report the radioactivity level of main building materials of China.� The radiation hazards of building materials are evaluated.� Roof tile and glazed tile should be limited to use in construction of buildings.� Monitoring on radioactivity level of cement made from fly ash should be intensified.

a r t i c l e i n f o

Article history:Received 10 November 2013Accepted 22 February 2014Available online 4 March 2014

Keywords:RadioactivityRadiation hazardRadium equivalent activityAnnual effective doseBuilding material

a b s t r a c t

The concentrations of 226Ra, 232Th and 40K in the commonly used building materials of Weinan, Chinawere measured using γ-ray spectrometry. The associated radiological hazards of natural radioactivity inthe studied materials were evaluated by radium equivalent activity, external hazard index, internalhazard index, indoor air absorbed dose rate and annual effective dose rate. The measurement resultsshow that the natural radionuclides contents of the studied building materials are in the range of Chinesesoil values. The radium equivalent activity and external hazard index values of glazed tile are close to orhigher than the recommended limit. The internal hazard index values and the annual effective dose ratevalues of roof tile, glazed tile and some cement samples made from fly ash are close to or higher thanunity and 1 mSv y�1, respectively. The study shows that roof tile and glazed tile should be limited to usein the construction of building and the monitoring on the natural radioactivity level of cement madefrom fly ash should be intensified for avoiding unnecessary radiation exposure to residents.

& 2014 Elsevier Ltd. All rights reserved.

1. Introduction

Natural radionuclides, ubiquitously spread in the natural envir-onment (UNSCEAR, 2000; Matiullah et al., 2004; Singh et al.,2005), consist of three well-known radioactive series, i.e. theuranium series originates with 238U, the thorium series originateswith 232Th and the actinium series originates with 235U (Ahmadet al., 1997; Khatibeh et al., 1997). There are also several singlyoccurring radionuclides; the most important one is 40K because itis a gamma-ray emitter in addition to beta decays and thereforecontributes significantly to the gamma radiation exposure. Themembers of the radioactive decay chains of 232Th (14%), 235U and238U (55.8%), along with 40K (13.8%) are responsible for the maincontributions to the dose from natural radiation (Bruzzi et al.,1997). As the 235U to 238U ratio is less than 1% (Chiozzi et al., 2000),

the contribution of 235U to the environmental dose is very small.Since 98.5% of the radiological effects of the uranium series areproduced by 226Ra and its daughter products, the contributionfrom the 238U and the other 226Ra precursors are normally ignored(Turhan, 2008).

Building materials, derived from rock, sand, soil and byproductof industry, often contain varying amounts of natural radionu-clides (Matiullah et al., 2004; Rahman et al., 2013; Sharaf andHamideen, 2013). The knowledge of the natural radioactivity levelof building materials is important for determination of populationexposure to radiation, as most of the residents spend about 80% oftheir time indoors (Stoulos et al., 2003). Furthermore, knowledgeof this radioactivity is useful in setting the standards and nationalguidelines for the use and management of these materials and inassessing the associated radiation hazard to human health. Build-ing materials contribute to environmental radioactivity in twoways. First, by gamma-radiation, mainly from 226Ra, 232Th, 40K andtheir progenies to a whole body dose and in some cases by betaradiation to a skin dose, and second by radon exhalation to aninternal dose exposure due to the deposition of radon decay

Contents lists available at ScienceDirect

journal homepage: www.elsevier.com/locate/radphyschem

Radiation Physics and Chemistry

http://dx.doi.org/10.1016/j.radphyschem.2014.02.0210969-806X & 2014 Elsevier Ltd. All rights reserved.

n Corresponding to: School of Tourism and Environment, Shaanxi NormalUniversity, No. 199, Chang’an Road, Xi’an 710062, Shaanxi Province, People'sRepublic of China. Tel.: þ86 2985 310525; fax: þ86 2985 303883.

E-mail address: luxinwei@snnu.edu.cn (X. Lu).

Radiation Physics and Chemistry 99 (2014) 62–67

products in the human respiratory tract (Faheem et al., 2008).Elevated dose rates indoors may arise from high activities ofnatural radionuclides in building materials. The natural radio-activity level of building materials can vary considerably accordingto the geological locations and geochemical characteristics ofthose materials. Therefore, it is necessary to determine the naturalradioactivity level of building materials from different areas. Dueto the increasing social concern, the natural radioactivity level ofbuilding materials has been reported in many countries (Beretkaand Mathew, 1985; Ngachin et al., 2007; Faheem et al., 2008;El-Taher et al., 2010; Hussain et al., 2010; Mavi and Akkurt, 2010;Moharram et al., 2012; Al-Sulaiti et al., 2011; Damla et al., 2011;Ravisankar et al., 2012; Rahman et al., 2013; Sharaf and Hamideen,2013; Tufan and Dişci, 2013), including some Chinese areas (Zhaoet al., 2012; Yang et al., 2013). The aims of the study are todetermine the concentration of natural radionuclide in the com-monly used building materials in Weinan, China and to evaluatethe associated radiation hazards to individuals by using radiumequivalent activity, external and internal hazard indexes, indoorair absorbed dose rate and annual effective dose rate. The resultsare compared with the internationally approved values.

2. Materials and methods

2.1. Samples

The samples investigated are red-clay brick (RCB), sand (S),gravel aggregate (GA), cement (C), ceramic tile (CT), roof tile (RT)and glazed tile (GT) which are the commonly used building

materials in Weinan. The investigated building material sampleswere collected directly from the local building material suppliers,manufacturers and construction sites. Five to ten samples of eachtype of the investigated building materials were collected. Allsamples were crushed and pulverized to less than 0.16 mm, exceptfor cement samples. Each sample was homogenized and dried inan oven at 105 1C for 8–12 h to remove moisture. The preparedsamples were transferred to radon impermeable polyethylenecontainers (7.0 cm height and 6.5 cm diameter), weighed andsealed for 4–5 weeks to allow for radium, thorium and theirshort-lived progenies to reach radioactive equilibrium (Lu et al.,2012).

2.2. Radioactivity measurement

The concentrations of natural radionuclides 226Ra, 232Th and40K in the investigated building materials were determined using a3�3 in. NaI (Tl) gamma-ray spectrometric system with excel 8%energy resolution (137Cs 661.6 keV). The detector, housed in acylindrical shield with a thickness of 10.5 cm and a height of38 cm, was coupled to a 1024 microcomputer multi-channel pulseheight analyzer and the system was calibrated for the γ-energyrange 50 keV to 3.2 MeV (Lu et al., 2012). The activity of 232Th wasdetermined by 238.6 keV and 2614 keV gamma rays emitted from212Pb and 208Tl, respectively. The activity of 226Ra was measured by609.3 and 1764.5 keV gamma rays emitted from 214Bi, whereas 40Kactivity was measured directly through its gamma ray energy peakof 1460.8 keV. The standard sources for 226Ra and 232Th (in secularequilibrium with 228Th) were prepared using known activitycontents and mixing with the matrix material of phthalic acidpowder. To avoid the loss of gaseous daughter products of 226Raand 232Th which may lead to disturbance in radioactive equili-brium, the prepared standard sources were kept in sealed cylind-rical polyethylene containers (7.0 cm height and 6.5 cm diameter).Analar grade potassium chloride (KCl) of a known amount of thesame geometry was used as the standard source of 40K. Allsamples were counted for 18,000 s (Zhao et al., 2012; Yang et al.,2013). Each sample was counted four times before an average wascalculated.

2.3. Radiological hazard assessment

The distribution of 226Ra, 232Th and 40K in building materials isnot uniform. To compare the activity concentrations and assess theradiological hazard of the building materials, the radium equiva-lent activity (Raeq), defined according to the estimation that1 Bq kg�1 of 226Ra, 0.7 Bq kg�1 of 232Th and 13 Bq kg�1 of 40Kproduce the same gamma ray dose Beretka and Mathew (1985), is

Table 1Activity concentrations of 226Ra, 232Th and 40K in building materials of Weinan, China.

Materials Activity concentration (Bq kg�1)

226Ra 232Th 40K

Range Mean7SD Range Mean7SD Range Mean7SD

Cement (C) 97.2–131.3 118.7714.2 20.9–61.8 36.1717.8 354.6–629.6 444.57163.1Sand (S) 15.6–72.3 32.5721.6 28.4–61.1 47.7712.1 180.8–274.1 249.6722.8Red-clay brick (RCB) 118.9–130.5 124.7715.3 27.8–30.1 28.971.4 377.3–417.6 390.279.8Gravel aggregate (GA) 91.0–124.8 96.177.6 11.8–27.4 17.276.8 280.7–398.5 326.8746.7Ceramic tile (CT) 49.6–94.8 69.4729.0 23.2–52.5 38.7710.2 285.5–644.3 417.47167.6Roof tile (RT) 150.4–173.4 160.479.7 34.7–49.2 38.876.4 515.4–625.3 568.3747.4Glazed tile (GT) 226.3–266.1 233.178.6 42.1–64.2 49.3710.8 772.6–835.1 795.5729.1

SD: Standard deviation.

Fig. 1. The relative concentration of 226Ra, 232Th and 40K to the total activity inbuilding materials.

X. Lu et al. / Radiation Physics and Chemistry 99 (2014) 62–67 63

used. This index Raeq is given as

Raeq ¼ CRaþ1:43CThþ0:077Ck ð1Þ

where CRa, CTh and CK are the activity concentrations of 226Ra,232Th and 40K in Bq kg�1, respectively.

To limit the external gamma radiation dose from buildingmaterials to 1.5 mSv y�1, the external hazard index (Hex) isdefined as (Beretka and Mathew, 1985)

Hex ¼ ðCRa=370ÞþðCTh=259ÞþðCK=4810Þ ð2Þwhere CRa, CTh and CK are the activity concentrations of 226Ra,232Th and 40K in Bq kg�1, respectively. The value of this indexmust be less than unity for the radiation hazard to be negligible.For the maximum value of Hex to be less than unity, the maximumvalue of Raeq must be less than 370 Bq kg�1.

In addition to the external hazard, radon and its short-livedproducts are also hazardous to the respiratory organs. The internal

exposure to radon and its daughter products is quantified by theinternal hazard index (Hin) which is defined as (Beretka andMathew, 1985)

Hin ¼ ðCRa=185ÞþðCTh=259ÞþðCK=4810Þ ð3Þwhere CRa, CTh and CK are the activity concentrations of 226Ra,232Th and 40K in Bq kg�1, respectively. For the safe use of amaterial in the construction of dwellings, Hin should be lessthan unity.

The indoor air absorbed dose rate (D) due to gamma rayemission from the natural radionuclides in the building materialsis evaluated according to the report of EC (1999)

DðnGy h�1Þ ¼ 0:92CRaþ1:1CThþ0:08CK ð4Þwhere CRa, CTh and CK are the activity concentrations of 226Ra,232Th and 40K in Bq kg�1, respectively. To estimate the annualeffective dose, the conversion coefficient (0.7 Sv Gy�1) from the

Fig. 2. Comparison of natural radionuclides concentrations in cement from different cities of Guanzhong, China.

Fig. 3. Comparison of natural radionuclides concentrations in sand from different cities of Guanzhong, China.

X. Lu et al. / Radiation Physics and Chemistry 99 (2014) 62–6764

absorbed dose in air to the effective dose received by individualand the indoor occupancy factor (0.8) proposed by UNSCEAR(2000) are used. The annual effective dose rate (AED) is calculatedas

AED ðmSv y�1Þ ¼D ðnGy h�1Þ � 8760ðhÞ � 0:8

� 0:7ðSv Gy�1Þ � 10�6 ð5Þ

3. Results and discussion

3.1. Specific activity

The range, mean value and standard deviation (SD) of 226Ra,232Th and 40K concentrations in the investigated building materi-als are shown in Table 1. As shown in Table 1, the activity

concentrations of 226Ra, 232Th and 40K in the main buildingmaterials range from 15.6 to 266.1, 11.8 to 64.2 and 180.8 to835.1 Bq kg�1, respectively. The 226Ra concentrations in all studiedbuilding materials except for sand are higher than 232Th concen-trations. The concentrations of 226Ra, 232Th and 40K occupy thetotal activity of 10% in sand (S) to 23% in red-clay brick (RCB), 4% ingravel aggregate (GA) to 14% in sand (S) and 72% in red-clay brick(RCB) to 79% in ceramic tile (CT), respectively (Fig. 1), whichindicates that the specific activity due to 40K is the largestcontributor to the total activity for all samples. The results foreach radionuclide were compared with the average activity con-centration for Chinese soil and the worldwide soil (UNSCEAR,2000). The 226Ra average concentrations in all commonly usedbuilding materials except for sand are higher than that of theworldwide population-weighted average value (32 Bq kg�1) forsoil (UNSCEAR, 2000), while the mean activity concentrations of232Th in all commonly used building materials are lower than or

Fig. 4. Comparison of natural radionuclides concentrations in red-clay brick from different cities of Guanzhong, China.

Table 2The calculated value of radiological hazard index in building materials of Weinan, China.

Materials Statistics Raeq (Bq kg�1) Hex Hin D (nGy h�1) AED (mSv y�1)

Cement Min 154.4 0.42 0.68 140.8 0.691Max 268.2 0.72 1.08 239.1 1.173Mean7SD 204.5752.2 0.5570.14 0.8770.18 184.5745.7 0.90570.224

Sand Min 70.1 0.19 0.23 60.1 0.295Max 180.8 0.49 0.68 155.7 0.764Mean7SD 119.9740.7 0.3270.11 0.4170.17 102.3735.0 0.50270.172

Red-clay brick Min 187.7 0.51 0.83 170.2 0.835Max 205.7 0.56 0.91 186.6 0.915Mean7SD 196.1718.1 0.5370.05 0.8770.09 177.7716.4 0.87270.080

Gravel aggregate Min 129.5 0.35 0.60 119.2 0.585Max 194.7 0.53 0.86 176.8 0.867Mean7SD 145.9720.9 0.3970.06 0.6570.08 133.5718.2 0.65570.089

Ceramic tile Min 104.8 0.28 0.42 94.0 0.461Max 219.5 0.59 0.85 196.5 0.964Mean7SD 156.9756.6 0.4270.15 0.6170.23 139.8751.4 0.68670.252

Roof tile Min 239.7 0.65 1.05 217.8 1.068Max 291.9 0.79 1.26 263.7 1.293Mean7SD 259.6722.5 0.7070.06 1.1370.09 235.7719.8 1.15670.097

Glazed tile Min 346.0 0.93 1.55 316.3 1.552Max 422.2 1.14 1.86 382.2 1.875Mean7SD 364.9726.3 0.9970.07 1.6270.09 332.3722.1 1.63070.108

X. Lu et al. / Radiation Physics and Chemistry 99 (2014) 62–67 65

slightly higher than that of the worldwide population-weightedaverage value (45 Bq kg�1) for soil (UNSCEAR, 2000). Similarly for40K, the mean activity concentrations obtained for roof tile andglazed tile are higher, while for cement, sand, red-clay brick, gravelaggregate and ceramic tile are lower than or close to the world-wide population-weighted average value (420 Bq kg�1) for soil(UNSCEAR, 2000). The activity concentrations of 40K, 226Ra and

232Th in all samples are in the range of Chinese soil values(UNSCEAR, 2000).

Cement, sand and red-clay brick are the most commonly usedmaterials in building construction. Figs. 2–4 present the compar-ison of natural radionuclides concentrations in these materialsfrom Xi’an (Lu, 2005), Xianyang (Lu et al., 2012), Baoji (Lu andZhang, 2008) and Weinan which are the main four cities ofGuanzhong (Shaanxi province), China. As shown in Fig. 2, themean concentrations of 226Ra and 40K in cement of Weinan are allhigher than other three cities and the mean concentration of 232Thin cement of Weinan is lower than Xi’an and close to Xianyang andBaoji. Fig. 3 indicates that the mean value of 226Ra in sand ofWeinan is lower than that in sand of Xi’an, and higher than that insand of Xianyang and Baoji, whereas the mean concentrations of232Th and 40K in sand of Weinan are respectively higher than andlower than those of other compared cites. As can be seen fromFig. 4, the mean value of 226Ra in red-clay brick of Weinan is higherthan other three cities, while the mean concentrations of 232Thand 40K are all lower than other three cities. The difference ofnatural radioactivity level in cement, sand and red-clay brick offour cities is related to their sources and the chemical properties oftheir raw materials.

3.2. Radiological hazard assessment results

The radiological hazard of natural radionuclides in the studybuilding materials to residents was evaluated using radium equivalentactivity (Raeq), external hazard index (Hex), internal hazard index (Hin),indoor air absorbed dose rate (D) and annual effective dose rate (AED).The calculated results of Raeq, Hex, Hin, D and AED for the commonlyused building materials in Weinan are presented in Table 2. The Raeqvalues range from 70.1 Bq kg�1 in sand to 422.2 Bq kg�1 in glazedtile, which are lower than the recommended limit of 370 Bq kg�1 forbuilding materials (UNSCEAR, 2000) except for glazed tile. Thecalculated values of Hex for the studied building materials range from0.19 to 1.14 as shown in Table 2. It can be found that the Hex values forall investigated building materials except for glazed tile are less thanunity. The natural radionuclides concentrations of glazed tiles aresignificantly higher than other investigated building materials. TheRaeq values of glazed tile samples are close to or higher than therecommended limit (370 Bq kg�1) and their Hex values are close to orlarger than unity. The calculated results of the relative contributionsof 226Ra, 232Th and 40K to Raeq and Hex for the commonly usedbuilding materials in Weinan show that the relative contributions of226Ra, 232Th and 40K to Raeq and Hex are the same. As shown in Fig. 5,232Th is the main contributor to Raeq and Hex in sand, while 226Ra ismain contributor to Raeq and Hex in other building materials. The sumof the relative contribution of 226Ra and 232Th to Raeq and Hex is 80–85% in all analyzed building materials. The calculated values of Hin forthe studied building materials range from 0.23 to 1.86 as shown inTable 2. The Hin values in roof tile, glazed tile and some cementsamples made from fly ash are close to or higher than unity, whilethose in other building materials are less than unity. Fig. 6 shows that226Ra is the main contributor to Hin in all building materials except forsand. The sum of the relative contribution of 226Ra and 232Th to Hin is86–91% in all analyzed building materials.

The estimated indoor air absorbed dose rate (D) values for theinvestigated building materials range from 60.1 nGy h�1 in sand to382.2 nGy h�1 in glazed tile as shown in Table 2. The average Dvalues of all investigated building materials are higher than theworld population-weighted average indoor absorbed gamma doserate of 84 nGy h�1 (UNSCEAR, 2000). The calculated values of AEDdue to gamma ray emission from 226Ra, 232Th and 40K in thestudied building materials range from 0.295 mSv y�1 in sand to1.875 mSv y�1 in glazed tile as shown in Table 2. The AED values inroof tile, glazed tile and some cement samples made from fly ash

Fig. 5. The relative concentration of 226Ra, 232Th and 40K to Raeq and Hex in buildingmaterials.

Fig. 6. The relative concentration of 226Ra, 232Th and 40K to Hin in buildingmaterials.

Fig. 7. The relative concentration of 226Ra, 232Th and 40K to D and AED in buildingmaterials.

X. Lu et al. / Radiation Physics and Chemistry 99 (2014) 62–6766

exceed the recommended limit of 1 mSv y�1 (EC, 1999). Therelative contributions of 226Ra, 232Th and 40K to D are the sameto AED. 226Ra is the main contributor to D in all building materialsexcept for sand. The sum of the relative contribution of 226Ra and232Th to D is 76–81% in all analyzed building materials (Fig. 7). Inbuilding material industry of Weinan, fly ash from coal-firedpower plant, containing higher natural radioactivity (Lu andZhang, 2008), was often used to produce cement, glazed tile androof tile. These materials should be limited to use as buildingmaterials for building construction according to the fore radiationassessment results.

4. Conclusions

The measurement results of natural radioactivity in the com-monly used building materials of Weinan, China show that thespecific activities of 226Ra, 232Th and 40K range from 15.6 to 266.1,11.8 to 64.2 and 180.8 to 835.1 Bq kg�1, respectively, which are inthe range of Chinese soil values. 40K is the largest contributor tothe total activity for all samples. The natural radioactivity level ofglazed tile is significantly higher than other investigated buildingmaterials. The difference of natural radioactivity level in cement,sand and red-clay brick between Weinan and other three maincities of Guanzhong is related to their sources and the chemicalproperties of their raw materials. The radium equivalent activityand external hazard index values of glazed tile are close to orhigher than the recommended limit. The internal hazard indexvalues of roof tile, glazed tile and some cement samples madefrom fly ash exceed or close to unity. The average values of indoorair absorbed dose rate for all building materials are higher than theworld population-weighted average indoor absorbed gamma doserate of 84 nGy h�1 and the annual effective dose rate values of rooftile, glazed tile and some cement samples made from fly ashexceed the recommended limit of 1 mSv y�1. The results showthat roof tile and glazed tile should be limited to use in theconstruction of building and the monitoring on the natural radio-activity level of cement made from fly ash should be intensified,whereas other main building materials do not pose any significantsource of radiation hazard and are safe for use in the constructionof building.

Acknowledgments

This work was supported by the Fundamental Research Fundsfor the Central Universities through Grant GK200901008. Allexperiments were completed in the Environmental RadioactivityLaboratory of Shaanxi Normal University. Gratitude is expressed toG. Yang, L. Pang and C. Zhao for their help with sample preparationand experiments.

References

Ahmad, N., Matiullah, Khatibeh, A.J.A.H., Ma’ly, A., Kenwy, M.A., 1997. Measurementof natural radioactivity in Jordanian sand. Radiat. Meas. 28, 341–344.

Al-Sulaiti, H., Alkhomashi, N., Al-Dahan, N., Al-Dosari, M., Bradley, D.A., Bukhari, S.,Matthews, M., Regan, P.H., Santawamaitre, T., 2011. Determination of the

natural radioactivity in Qatarian building materials using high-resolutiongamma-ray spectrometry. Nucl. Instrum. Methods Phys. Res. A 652, 915–919.

Beretka, J., Mathew, P.J., 1985. Natural radioactivity of Australian building materials,industrial wastes and by-products. Health Phys. 48, 87–95.

Bruzzi, L., Baroni, M., Mele, R., Nani, E., 1997. Proposal for a method of certificationof natural radioactivity in building materials. J. Radiol. Prot. 17, 85–94.

Chiozzi, P., Felice, P.D., Fazio, A., Pasquale, V., Verdoya, M., 2000. Laboratoryapplication of NaI(Tl) γ-ray spectrometry to studies of natural radioactivity ingeophysics. Appl. Radiat. Isot. 53, 127–132.

Damla, N., Cevik, U., Kobya, A.I., Celik, A., Celik, N., Yıldırım, I., 2011. Assessment ofnatural radioactivity and mass attenuation coefficients of brick and roofing tileused in Turkey. Radiat. Meas. 46, 701–708.

EC, 1999. Radiological protection principles concerning the natural radioactivity ofbuildings materials. European Commission (Radiation Protection Report 112),Directorate-General Environment, Nuclear Safety and Civil Protection.

El-Taher, A., Makhluf, S., Nossair, A., Abdel Halim, A.S., 2010. Assessment of naturalradioactivity levels and radiation hazards due to cement industry. Appl. Radiat.Isot. 68, 169–174.

Faheem, M., Mujahid, S.A., Matiullah, 2008. Assessment of radiological hazards dueto the natural radioactivity in soil and building material samples collected fromsix districts of the Punjab province-Pakistan. Radiat. Meas. 43, 1443–1447.

Hussain, H.H., Hussain, R.O., Yousef, R.M., Shamkhi, Q., 2010. Natural radioactivity ofsome local building materials in the middle Euphrates of Iraq. J. Radioanal.Nucl. Chem. 284, 43–47.

Khatibeh, A.J.A.H., Ahmad, N., Matiullah, Kenawy, A., 1997. Natural radioactivity inmarble stones-Jordan. Radiat. Meas. 28, 345–348.

Lu, X., 2005. Natural radioactivity in some building materials of Xi’an, China. Radiat.Meas. 40, 94–97.

Lu, X., Zhang, X., 2008. Radionuclide content and associated radiation hazards ofbuilding materials and by-products in Baoji, West China. Radiat. Prot. Dosim.128, 471–476.

Lu, X., Yang, G., Ren, C., 2012. Natural radioactivity and radiological hazards ofbuilding materials in Xianyang, China. Radiat. Phys. Chem. 81, 780–784.

Matiullah, Ahad, A., Rehman, S., Rehman, S., Feheem, M., 2004. Measurement ofradioactivity in the soil of Bahawalpur division, Pakistan. Radiat. Prot. Dosim.112, 443–447.

Mavi, B., Akkurt, I., 2010. Natural radioactivity and radiation hazards in somebuilding materials used in Isparta, Turkey. Radiat. Phys. Chem. 79, 933–937.

Moharram, B.M., Suliman, M.N., Zahran, N.F., Shennawy, S.E., El Sayed, A.R., 2012.External exposure doses due to gamma emitting natural radionuclides in someEgyptian building materials. Appl. Radiat. Isot. 70, 241–248.

Ngachin, M., Garavaglia, M., Giovani, C., Njock, M.G.K., Nourreddine, A., 2007.Assessment of natural radioactivity and associated radiation hazards in someCameroonian building materials. Radiat. Meas. 42, 61–67.

Rahman, S.U., Rafique, M., Jabbar, A., Matiullah, 2013. Radiological hazards due tonaturally occurring radionuclides in the selected building materials used for theconstruction of dwellings in four districts of the Punjab Province, Pakistan.Radiat. Prot. Dosim. 153, 352–360.

Ravisankar, R., Vanasundari, K., Chandrasekaran, A., Rajalakshmi, A., Suganya, M.,Vijayagopal, P., Meenakshisundaram, V., 2012. Measurement of natural radio-activity in building materials of Namakkal, Tamil Nadu, India using gamma-rayspectrometry. Appl. Radiat. Isot. 70, 699–704.

Sharaf, J.M., Hamideen, M.S., 2013. Measurement of natural radioactivity inJordanian building materials and their contribution to the public indoor gammadose rate. Appl. Radiat. Isot. 80, 61–66.

Singh, S., Rani, A., Mahajan, R.K., 2005. 226Ra, 232Th and 40K analysis in soil samplesfrom some areas of Punjab and Himachel Pradesh, India using gamma rayspectrometry. Radiat. Meas. 39, 431–439.

Stoulos, S., Manolopoulou, M., Papastefanou, C., 2003. Assessment of naturalradiation exposure and radon exhalation from building materials in Greece.J. Environ. Radioact. 69, 225–240.

Tufan, M.Ç., Dişci, T., 2013. Natural radioactivity measurements in buildingmaterials used in Samsun, Turkey. Radiat. Prot. Dosim. 156, 87–92.

Turhan, Ş., 2008. Assessment of the natural radioactivity and radiological hazards inTurkey cement and its raw materials. J. Environ. Radioact. 99, 404–414.

UNSCEAR, 2000. Sources and effects of ionizing radiation. United Nations ScientificCommittee on Effects of Atomic Radiation. United Nations Publication, NewYork, USA (Report to the General Assembly with Scientific Annexes), 2000Reports.

Yang, G., Lu, X., Zhao, C., Li, N., 2013. Natural radioactivity in building materials usedin Changzhi, China. Radiat. Prot. Dosim. 155, 512–516.

Zhao, C., Lu, X., Li, N., Yang, G., 2012. Natural radioactivity measurements of buildingmaterials in Baotou, China. Radiat. Prot. Dosim. 152, 434–437.

X. Lu et al. / Radiation Physics and Chemistry 99 (2014) 62–67 67