Radiation Measurements 40 (2005) 94–97www.elsevier.com/locate/radmeas

Natural radioactivity in some building materials of Xi’an, China

Lu Xinwei∗College of Tourism and Environment, Shaanxi Normal University, Xi’an 710062, P. R. China

Received 29 March 2004; received in revised form 23 December 2004; accepted 3 January 2005

Abstract

Eight kinds of building materials collected from Xi’an, China were analyzed for the natural radioactivity of226Ra,232Thand40K using�-ray spectroscopy. The concentrations of226Ra,232Th and40K in the selected building materials ranges from19.5 to 68.3 Bq kg−1, 13.4 to 51.7 Bq kg−1 and 63.2 to 713.9 Bq kg−1, respectively. The measured activity concentrationsfor these natural radionuclides were compared with the reported data of other countries and with the world average activityof soil. The radium equivalent activities (Raeq), external hazard index (Hex) and the internal radiation hazard index (Hin)associated with the natural radionuclides were calculated. The Raeq values of all building materials are lower than the limitof 370 Bq kg−1, equivalent to a�-dose of 1.5 mSv yr−1. The values ofHex andHin are less than unity.© 2005 Elsevier Ltd. All rights reserved.

Keywords:Natural radioactivity; Building materials;�-spectrometry; Radium-equivalent activities; External hazard index; Internal hazardindex

1. Introduction

The naturally occurring radionuclides present in buildingmaterials including soil are226Ra,232Th and40K (Khan etal., 1998; Nageswara Rao, 1989),which are the main sourcesof radiation of building materials. These radionuclides poseexposure risks externally due to their�-ray emissions andinternally due to radon and its progeny which emit alphaparticles (Iqbal et al., 2000). In order to be able to assessradiological risk, it is important to study the levels of radi-ation emitted from building materials.

The natural radioactivity of building materials in someChinese areas and many countries have been reported(Amrani and Tahtat, 2001; Hayumbu et al., 1995; Hewa-manna et al., 2001; Ibrahim, 1999; Jiguan et al., 1997;Kumar et al., 1999, 2003; Nageswara Rao et al., 1996;Xiulan, 1999). However, the detailed information of Xi’anbuilding materials were not available. Therefore, systematic

∗ Tel.: +86 029 85303883; fax: +86 029 85303798.E-mail addresses:luxinwei@snnu.edu.cn,

luxinwei88@yahoo.com.cn, xwlzxl@sina.com(L. Xinwei).

1350-4487/$ - see front matter © 2005 Elsevier Ltd. All rights reserved.doi:10.1016/j.radmeas.2005.01.003

studies were performed and the activities of226Ra, 232Thand40K in building materials have been determined. In thispaper, we present the results for the measured activities,the radium equivalent concentrations and the values of boththe internal and external hazard indices associated with theusage of eight kinds of building materials collected fromXi’an, China. The results obtained in the present study arecompared with the findings of other studies.

2. Experimental methods

2.1. Samples

The building materials investigated are cement, cementplaster, cement brick, red-clay brick, sand, gravel aggregate,lime/limestone, and roof asbestos, which are the dominantbuilding materials in Xi’an. Samples with large grain sizewere crushed and milled to a fine powder with a particle sizeless than 0.16 mm, except for the cement, cement plasterand sand samples. Each of the materials was homogenizedand air dried and approximately 500 g then was sealed in gas

L. Xinwei / Radiation Measurements 40 (2005) 94–97 95

tight, radon impermeable, cylindrical polyethylene plasticcontainers (7.5 cm height and 10.5 cm diameter). Their netweights were recorded. These samples were then stored for30–40 days before counting so as to ensure Ra and its short-lived progeny to reach radioactive equilibrium (Amrani andTahtat, 2001; Khan and Khan, 2001; Kumar et al., 1999,2003).

2.2. Radioactivity measurement

The concentration of the natural radioactivity (226Ra,232Th and40K) in the material samples were determinedusing a 12.5 × 10 cm NaI(Tl) �-ray spectrometric systemwith 20% counting efficiency. The equipment used in thestudy is CIT-2000 low frequency�-ray spectromonitormade in Chengdu (China). The detector is maintained ina vertical position in a lead cylindrical shield of 10 cmthickness and 55 cm height. The internal dimensions of thefree surface within the shielding enclosure are 13 cm indiameter and 15 cm in depth. The detector was coupled toa 256 multichannel pulse height analyzer and the systemwas calibrated for the�-energy range 80 KeV to 3.2 MeV.The energy region for40K, 1.46 MeV �-rays, 226Ra,1.76 MeV�-rays and232Th, 2.62 MeV�-rays were chosenas 1.39–1.59; 1.64–1.98 and 2.42–2.68 MeV, respectively.The standard sources for226Ra and232Th (in secular equi-librium with 228Th) were prepared using known activitycontents and mixing with the matrix material of phthalicacid powder. In order to avoid the loss of gaseous daughterproducts of226Ra and228Th which may lead to disturbancein radioactive equilibrium, the prepared standard sourceswere kept in sealed plastic container (7.5 cm height and10.5 cm diameter). Analar grade potassium chloride (KCl)of a known amount of the same geometry was used asthe standard source of40K. The samples were counted forabout 400–600 min depending on the levels present in thesamples. To obtain net counts, background was subtractedusing the method ofRamachandran and Subba Ramu(1989). The counts due to each element were converted toconcentrations using standardized source parameters. Eachsample was counted twice before an average was taken.

3. Results and discussion

The activity concentrations of226Ra,232Th and40K, to-gether with standard deviation (SD), in various building ma-terials are given inTable 1. As shown inTable 1, the activ-ity concentrations of226Ra in all building materials exceedthat of the world average for soil (25 Bq kg−1) (UNSCEAR,1982), except for lime/limestone (19.5 Bq kg−1). The activ-ity concentration of226Ra in cement, cement brick, cementplaster, red-clay brick and sand exceed that of the Shaanxisoil (34.8 Bq kg−1) (Yaoming et al., 1994). The activity con-centrations of232Th in cement, cement plaster and red-claybrick exceed that of the world average of 25 Bq kg−1 for

soil (Ibrahim, 1999) and the Shaanxi soil (46.7 Bq kg−1)(Yaoming et al., 1994). Similarly for 40K activities the ac-tivity concentrations obtained for all building materials, ex-cept for red-clay brick (713.9 Bq kg−1), are lower than theworld average value (370 Bq kg−1) (Ibrahim, 1999) and theShaanxi average value(604.2 Bq kg−1) (Yaoming et al.,1994) for soil.

To assess the radiological risk of the building mate-rials used, it is useful to calculate an index called theradium equivalent activity (Beretka and Mathew, 1985;Malanca et al., 1993), Raeq, defined according to the es-timation 370 Bq kg−1 226Ra, 259 Bq kg−1 of 232Th or4810 Bq kg−1 of 40K produce the same�-ray dose. Thecalculated values of the radium equivalent Raeq for thestudied building materials are given inTable 1. These valuesrange from 46.6 to 178.3 Bq kg−1.

To limit the external�-radiation dose from building ma-terials to 1.5 mSv yr−1, the external hazard index (Hex)is defined by some workers (Beretka and Mathew, 1985;Hayumbu et al., 1995). The value of this index must be lessthan unity for the radiation risk to be negligible (Hayumbuet al., 1995). For the maximum value ofHex to be lessthan unity, the maximum value of Raeq must be less than370 Bq kg−1. According to the calculated equation ofHex(Beretka and Mathew, 1985; Hayumbu et al., 1995), the val-ues ofHex for the studied building materials range from0.118 to 0.501 as shown inFig. 1, values which indeed areless than unity. However, in Chinese criteria (GB6566-2001,2002) the calculated values ofHex for the studied buildingmaterials range from 0.119 to 0.522.

In addition to the external hazard, radon and its short-lived products are also hazardous to the respiratory organs.The internal exposure to radon and its daughter products isquantified by the internal hazard index (Hin) which is de-fined byBeretka and Mathew (1985). If the maximum con-centration of radium is half that of the normal acceptablelimit, then Hin will be less than 1.0 (Beretka and Mathew,1985). For the safe use of a material in the constructionof dwellings, Hin should be less than unity. The calcu-lated values ofHin range from 0.170 to 0.660 as shownin Fig. 1. Once again, all these values are less than unity.The similar index (internal exposure index) proposed toserve as a criterion in P.R. China (GB6566-2001, 2002). InGB6566-2001 criterion, which only considers internal ex-posure, corresponds to a maximal226Ra activity concen-tration of 200 for the building materials. According to Chi-nese criterion, all values of internal exposure index are lessthan unity.

Table 1compares the reported values of radium equiv-alent activities for selected building materials from othercountries. As shown inTable 1, the values of radium equiv-alent activities obtained for cement and cement plaster inthis work are found to be the highest compared to those ofother countries. For red-clay brick and roof asbestos, thevalue of radium equivalent activities in this study is simi-lar to that obtained for the Zambian and Algerian samples.

96 L. Xinwei / Radiation Measurements 40 (2005) 94–97

Tabl

e1

Act

ivity

conc

entr

atio

nsof

build

ing

mat

eria

lsof

Xi’a

nan

dth

eco

mpa

rison

ofra

dium

equi

vale

ntac

tiviti

esw

ithot

her

stud

ies

Materials

ctivity

concentration(

g−1)

Ra e

q(B

qkg

−1)

226 R

a23

2 Th

40K

Xi’a

n,C

hina

Alg

eria

Aus

tral

iaG

erm

any

Indi

aZ

ambi

a(p

rese

ntst

udy)

(Am

rani

and

Taht

at,

2001

)(B

eret

kaan

dM

athe

w,

1985

)(K

riege

r,19

81)

(Kum

aret

al.,

2003

)(H

ayum

buet

al.,

1995

)

Cem

ent

68.3

±3.

651

.7±

5.4

173.

8±

8.6

162.

8±

6.3

112

115

7010

979

Cem

ent

bric

k46.

2±

4.6

28.4

±6.

213

7.4

±6.

698

.6±

3.2

Cem

ent

plas

ter

64.7±

2.7

48.7

±2.

316

1.3

±3.

415

6.7

±4.

210

115

4180

63G

rave

lag

greg

ate

28.5±

3.5

19.5

±6.

728

6.7

±7.

682

.6±

4.6

5811

532

224

Red

-cla

ybr

ick

58.6

±4.

750

.4±

3.5

713.

9±

8.2

178.

3±

6.2

190

883

640

180

San

d40

.7±

4.3

21.5

±5.

630

2.6

±3.

496

.4±

2.3

2870

5984

135

Lim

e/lim

esto

ne19.

5±

2.8

13.4

±3.

763

.2±

5.4

46.6

±2.

437

115

4879

33R

oof

asbe

stos

31.3±

6.4

15.4

±5.

215

6.8

±4.

363

.4±

3.4

5161

NumerofsamplesofXi’angivenin

racet:Cement(10)Cementric

(6)Cementplaster()

ravelaggregate

(12)Red-clay

ric

(11)Sand(9)Lime/limestone(9

)Roof

asestos(6).

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

cem

ent

cemen

t bric

k

cem

ent p

laster

grav

el ag

greg

ate

red-c

lay b

rick

sand

lime/l

imes

tone

roof

asbe

sto

Samples

Haz

ard

Inde

x

External Internal

ig. 1. The measured values of oth the external and the internalha ard indices for uilding materials collected from Xi’an, China.

In the case of lime/limestone, the result of this study is ofthe same order as the Algerian, German, Indian, and Zam-bian samples. The radioactivity in building materials variedfrom one country to another or even there are variations inthe radium equivalent activities of different materials andalso within the same type of materials. The results may beimportant from the point of view of selecting suitable ma-terials for use in building construction. Large variations inradium equivalent activities may suggest that it is advisableto monitor the radioactivity levels of materials from a newsource, before adopting it for using as a building material.

4. Conclusions

The radium equivalent activities obtained for the build-ing materials in this study were all below the criterion limitof �-radiation dose (1.5 mSv yr−1). The values of both theinternal and external hazard indices associated with the us-age of eight building materials collected from Xi’an, Chinaare less than unity. Therefore, the use of these materials inthe construction of dwellings is considered to be safe forinhabitants.

Acknowledgements

This work was supported by the Provincial Natural Sci-ences Foundation of Shaanxi through grants 2003D04 andby the Science Foundation of Shaanxi Normal University.Gratitude is expressed to Jia Xiaowei, Wang Xiaolei, LiZhende for assisting in sampling.

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