natural radioactivity in building materials used in changzhi, china
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NATURAL RADIOACTIVITY IN BUILDING MATERIALS USEDIN CHANGZHI, CHINAGuang Yang, Xinwei Lu*, Caifeng Zhao and Nan LiSchool of Tourism and Environment, Shaanxi Normal University, Xi’an 710062, People’s Republic of China
*Corresponding author: [email protected]
Received May 25 2012, revised November 28 2012, accepted January 23 2013
The natural radioactivity levels of the commonly used building materials collected from Changzhi, China was analysed usinggamma-ray spectroscopy. The activity concentrations of 226Ra, 232Th and 40K in the investigated building materials rangefrom 14.6 to 131.2, from 9.9 to 138.8 and from 96.1 to 819.0 Bq kg21, respectively. The results were compared with thereported data of other countries and with the worldwide mean activity of soil. The external and internal hazard indices andgamma index were calculated to assess the radiation hazard to residents. The external hazard index of all building materialsare less than unity, while the internal hazard and gamma indexes of hollow brick and gravel aggregate exceed unity. Thestudy shows that the investigated hollow brick and gravel aggregate are not suitable for use as building materials in dwellings.
INTRODUCTION
Natural radionuclides widely spread in the Earth’senvironment, e.g. rock, soil, water, air and plant(1, 2).Almost all building materials, derived from bothnatural sources (e.g. rock and soil) and waste pro-ducts (e.g. phosphogypsum, alum shale, coal fly ash,etc.) and also from industry by-products (e.g. powerplants, phosphate fertiliser and oil industry)(3),contain various amounts of natural radionuclides226Ra, 232Th and their progenies and 40K. The spe-cific activities of 226Ra, 232Th and 40K in the buildingmaterials mainly depend on geological and geograph-ical conditions as well as geochemical characteristicsof those materials. Elevated indoor external doserates may arise from the high specific activities ofnatural radionuclides in the building materials, whichis the main source of indoor gamma radiation besidesterrestrial and cosmic radiation(4). The natural radio-nuclides in building materials of dwellings, work-places and industrial buildings can cause externaland internal radiation exposure to people(5, 6). Theexternal radiation exposure is caused by directgamma radiation originating from natural radionu-clides, while the internal radiation exposure, affectingthe respiratory tract, is due to the inhalation of alphaparticles emitted from the short-lived radionuclidesradon (222Rn, the daughter product of 226Ra) andthoron (220Rn, the daughter product of 224Ra), whichemanate from building materials(5 –12).
Knowledge of the natural radioactivity in buildingmaterials is important in the assessment of any pos-sible radiological hazard to humans caused by theuse of specific building materials since most indivi-duals typically spend 80 % of their time indoors(4– 7).This knowledge is essential for the development ofstandards and guidelines concerning the use and
management of building materials. In recent decades,there are a lot of papers which report the naturalradionuclide content of building materials over theworld including some cities of China(4, 13–20).However, the detailed information about naturalradioactivity of building materials in Changzhi,China is scanty. Changzhi is one of the important in-dustrial cities of Central China, and there are about3 300 000 people living in Changzhi. The building in-dustries developed rapidly during the urbanisation ofChangzhi and some new building materials were usedin building construction. The aims of the presentstudy are to determine the natural radioactivity levelof the commonly used building materials ofChangzhi and to provide the basic information forthe use and management of these materials. The con-centrations of 226Ra, 232Th and 40K in the commonlyused building materials of Changzhi were analysedusing the gamma-ray spectrometry and the associatedradiation hazards to occupants were assessed by cal-culating the external and internal hazard indices andrepresentative gamma index. The results obtained inthe present study are compared with the recom-mended values and other countries.
EXPERIMENTAL METHODS
The investigated samples are the commonly usedbuilding materials of Changzhi, China, which arered-clay brick, hollow brick, sand, cement, roof as-bestos, concrete and gravel aggregate. Five to 10samples of each type building material were random-ly collected from construction sites as well as fromvarious agencies supplying raw materials for buildingconstruction. All samples were crushed and milled toa fine power with a particle size of ,0.16 mm. The
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Radiation Protection Dosimetry (2013), Vol. 155, No. 4, pp. 512–516 doi:10.1093/rpd/nct018Advance Access publication 13 February 2013
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samples were homogenised and dried in an oven at1058C for 12 h to remove moisture. Finally, the driedsamples were weighted and stored in gas-tight cylin-drical polyethylene containers (7.0 cm height and 6.5cm diameter) to limit the escape of radon. The wallthickness of container is 2.5 cm. The containers werecompletely sealed for 30 d to reach secular equilib-rium where the rate of decay of the radon daughtersbecomes equal to that of the parents.
The concentrations of 226Ra, 232Th and 40K in thesamples were measured by gamma-ray spectrometricsystem using a 3�3 inch NaI(Tl) detector with anenergy resolution of 7.5 % (137Cs 661.6 keV). Thecontainer with the sample was placed on the detect-or with a vertical position inside a cylindrical leadshield of 10.5 cm thickness and 38 cm height with afixed bottom and movable cover. The concentrationof 226Ra was determined through the photopeaks of214Bi (609.3 and 1764.5 keV), whereas the concen-tration of 232Th was assessed by the photopeaks of212Pb (238.6 keV) and 208Tl (2614 keV). The 40K ac-tivity was measured directly from its 1460.8 keVgamma-ray energy peak. The detection system wascalibrated using the standard materials supplied bythe BRIUG (Beijing Research Institute of UraniumGeology), China. The standard sources were pre-pared for 226Ra and 232Th (in secular equilibriumwith 228Th) by using the known activity contentsand mixing with the matrix material of phthalic acidpowder. Analar grade potassium chloride (KCl) of aknown amount of the same geometry was used asthe standard source of 40K. All the standard sourceswere sealed in the containers with same geometry asthe samples. Each sample was measured for 300 minand was counted four times before an average wascalculated.
RESULTS AND DISCUSSION
Activity concentration
Table 1 shows the range of the specific activity of226Ra, 232Th and 40K, as well as the average
concentration and the corresponding standard devi-ation (SD) in the building materials under investiga-tion. As shown in Table 1, the activityconcentrations of 226Ra, 232Th and 40K in the build-ing materials of Changzhi ranges from 14.6 to131.2, from 9.9 to 138.8 and from 96.1 to 819.0 Bqkg21, respectively. It is evident that the average con-centration of 226Ra, 232Th and 40K in concrete is thelowest. The highest mean value of 226Ra was foundin hollow brick (115.8+5.5 Bq kg21). Moreover, thehighest mean values of 232Th and 40K were found ingravel aggregate (125.8+18.7 Bq kg21) and red-claybrick (764.8+34.2 Bq kg21), respectively. The meanvalues of 226Ra and 232Th in all investigated buildingmaterials except for concrete and sand are higherthan that in the local cinnamon soil (31.9 and 47.2Bq kg21, respectively), while the mean values of 40Kin all the analysed building materials except for red-clay brick and sand are lower than that in the localcinnamon soil (578 Bq kg21)(21). The results of eachradionuclide were also compared with the average ac-tivity concentration for Chinese soil and the world-wide soil(2). The average activity concentrations of226Ra and 232Th in all the building materials exceedthat of the worldwide population-weighted averagevalues (32 and 45 Bq kg21, respectively) in soil(2),except for concrete and sand samples. The averageactivity concentrations of 40K in all the buildingmaterials, except for red-clay brick and sand, arelower than the worldwide population-weightedaverage values (420 Bq kg21) in soil(2). The activityconcentrations of 226Ra, 232Th and 40K in all thesamples are in the range of Chinese soil values(2).Table 2 shows the average concentrations of naturalradionuclides in the building materials from otherinvestigations for comparison(5, 9, 12, 13, 15, 22 – 27).
Assessment of radiation hazard from buildingmaterials
The external hazard index, internal hazard indexand gamma index were calculated in this study toassess the radiation hazards associated with the
Table 1. Mean activity concentrations and ranges of 226Ra, 232Th and 40K in building materials from Changzhi, China(Bq kg21).
Material 226Ra 232Th 40K
Range Mean+SD Range Mean+SD Range Mean+SD
Red-clay brick 43.1–61.4 53.7+5.3 60.2–94.8 83.1+11.7 700.9–819.0 764.8+34.2Hollow brick 106.8–123.4 115.8+5.5 102.3–110.6 103.8+4.0 265.9–337.4 301.8+21.8Roof asbestos 51.0–55.0 52.7+2.0 56.7–60.8 58.8+2.3 339.5–446.8 380.5+50.5Concrete 14.6–23.7 18.1+3.8 9.9–18.2 12.6+3.2 96.1–153.3 120.4+21.4Sand 20.0–23.8 22.1+1.5 28.5–32.5 30.4+1.4 652.2–750.3 703.6+41.6Cement 60.4–131.2 106.8+32.3 44.8–76.9 64.4+12.6 192.3–277.7 252.2+25.9Gravel aggregate 56.7–90.6 82.4+13.8 92.2–138.8 125.8+18.7 324.4–488.0 413.8+63.3
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Table 2. Comparison of activity concentration with other countries.
Material City, country Activity concentration (Bq kg21) References
226Ra 232Th 40K
Red-clay brick Turkey 34 34 462 (9)Pakistan 23 35 431 (15)Espirito Santo, Brazil 41.8 119.9 322 (22)Cuba 57 12 857 (23)Cameroon 49.6a 91 172 (24)Isparta, Turkey 58.9 11.7 248.8 (25)Algerian 65 51 675 (26)Changzhi, China 53.7 83.1 764.8 Present study
Roof asbestos Espirito Santo, Brazil 56.3 99.1 413 (22)Algerian 19 12 192 (26)Turkey 33.1 31.7 423.9 (9)Changzhi, China 52.7 58.8 380.5 Present study
Concrete Espirito Santo, Brazil 21.9 25.3 42 (22)Jordan 38 6 138 (13)Cuba 25 12 595 (23)Greece 35 17 383 (27)Changzhi, China 18.1 12.6 120.4 Present study
Sand Jordan 25.1 14.6 188.1 (13)Algerian 12 7 74 (26)Espirito Santo, Brazil 10.2 12.6 51 (22)Cameroon 14a 31 586 (24)Cuba 17 16 208 (23)Pakistan 20 29 383 (15)Changzhi, China 22.1 30.4 703.6 Present study
Cement Isparta, Turkey 26.1 10.4 129.7 (25)Algerian 41 27 422 (26)Greece 20 13 247 (27)Cuba 23 11 467 (23)Egypt 35.60 43.17 82.08 (5)India 98a 81 340 (12)Pakistan 25 37 245 (15)Cameroon 27a 15 277 (24)Changzhi, China 106.8 64.4 252.2 Present study
Gravel aggregate Isparta, Turkey 22.5 6.8 101.7 (25)Algerian 24 10 259 (26)Cuba 20 13 134 (23)Greece 11 12 140 (27)Changzhi, China 82.4 125.8 413.8 Present study
a238U.
Table 3. The calculated values of external and internal hazard indices of building materials and the gamma index.
Material Hex Hin Ig
Range Mean+SD Range Mean+SD Range Mean+SD
Red-clay brick 0.26–0.34 0.31+0.03 0.63–0.84 0.77+0.07 0.71–0.93 0.85+0.14Hollow brick 0.38–0.39 0.39+0.01 1.07–1.12 1.09+0.02 0.98–1.03 1.01+0.03Roof asbestos 0.22–023 0.22+0.01 0.58–0.60 0.59+0.01 0.58–0.63 0.59+0.04Concrete 0.05–0.08 0.06+0.01 0.14–0.22 0.17+0.04 0.13–0.21 0.27+0.07Sand 0.16–0.17 0.16+0.01 0.37–0.39 0.38+0.01 0.44–0.48 0.46+0.03Cement 0.19–0.35 0.29+0.07 0.56–1.05 0.88+0.23 0.51–0.90 0.76+0.35Gravel aggregate 0.29–0.43 0.40+0.06 0.73–1.10 1.02+0.16 0.76–1.14 1.04+0.31
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usage of the investigated building materials. The ex-ternal hazard index (Hex) is an important parameterto evaluate the hazard of natural gamma radiation.The prime objective of this index is to limit radiationdose to the normal dose equivalent limit of 1 mSvy21(28). Krieger(29) proposed one conservative modelwith infinitely thick wall and without windows anddoors to serve a criterion for the calculation.Hewamanna et al.(30) modified that model aftertaking the thickness of the wall and the existence ofthe windows and doors into consideration, and theHex is defined as
Hex ¼CRa
740þ CTh
520þ CK
9620ð1Þ
where CRa, CTh and CK are the activity concentra-tions of 226Ra, 232Th and 40K in Bq kg21, respect-ively. The value of the external hazard index shouldbe below unity for the radiation hazard to be negli-gible. The values of the Hex from the Equation (1)for all investigated building materials range from0.05 to 0.43 as shown in Table 3, values which areindeed less than unity.
In addition to the external irradiation, inhalationof alpha particles emitted from radon and its short-lived products is hazardous to the respiratory organstoo. This hazard can be quantified by the internalhazard index (Hin), which is defined as(31)
Hin ¼CRa
185þ CTh
259þ CK
4810ð2Þ
where CRa, CTh and CK are the activity concentra-tions of 226Ra, 232Th and 40K in Bq kg21, respect-ively. The internal hazard index must be below unityin order to provide safe levels of radon and its short-lived daughters for the respiratory organs of indivi-duals living in the dwellings. The values of Hin forthe investigated building materials range from 0.14to 1.12 as shown in Table 3. The Hin average valuesof hollow brick and gravel aggregate and the Hinvalues of some cement samples are slightly higherthan unity. The large Hin values of hollow brick,gravel aggregate and some cement samples arerelated to the higher concentrations of 226Ra and232Th in these building materials. Fly ash withhigher concentrations of 226Ra and 232Th, by-pro-ducts of coal-fired power plants, is often used asadditives to produce cement and hollow brick inChangzhi. The gravel aggregate used in Changzhi isshattered granite. According to Hin, the usage ofthese materials should be restricted in the construc-tion of dwellings.
The gamma index (Ig) proposed by the EuropeanCommission(32) is often used to assess the excessgamma radiation arising from building materials,
which is calculated using the following formula:
Ig ¼CRa
300þ CTh
200þ CK
3000ð3Þ
where CRa, CTh and CK are the activity concentra-tions of 226Ra, 232Th and 40K, in Bq kg21, respect-ively. Ig � 1 corresponds to an absorbed gammadose rate less or equal to 1 mSv y21, while Ig � 0.5corresponds to a dose rate less or equal to 0.3 mSvy21(32). The values of the range and mean Ig of theinvestigated building materials are presented inTable 3. The mean Ig values of all the building mate-rials except for concrete and sand are .0.5, especial-ly for hollow brick and gravel aggregate, the mean Igvalues of them are slightly .1. The results showthat hollow brick and gravel aggregate are not suit-able to be used as building materials in housesbecause they will cause excess gamma radiation toinhabitants.
CONCLUSION
The activity concentrations of 226Ra, 232Th and 40Kin the building materials from Changzhi, China,have been measured using NaI(Tl) gamma-ray spec-trometry. The external and internal hazard indicesand gamma index were calculated to assess the po-tential radioactive hazard of the building materials.The results show that the activity concentrations of226Ra, 232Th and 40K in all the building materialsare in the range of Chinese soil values. The externalhazard indexes of all the building materials are lessthan unity, while the internal hazard index andgamma index of hollow brick and gravel aggregateare slightly higher than unity. The study shows thatmost of the building materials do not pose any sig-nificant source of radiation hazard and are safe foruse in the construction of dwellings, while hollowbrick and gravel aggregate are not suitable for use inthe construction of dwellings.
ACKNOWLEDGEMENTS
Gratitude is expressed to C. Ren for his help withsample preparation and experiments. The authorsalso thank the editor and anonymous reviewers fortheir insightful suggestions and critical reviews ofthe manuscript.
FUNDING
This work was supported by the FundamentalResearch Funds for the Central Universities throughGrants GK200901008.
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