Radon Exhalation and radiological impact of building materials containing fly ASH

Abstract

The knowledge of the natural radioactivity of building materials is important for the determination of population exposure to radiations, as most of the residents spend about 80% of their time indoors, In controlling the natural radiation exposure for the residents of dwellings, it is necessary to detennine the levels of natllHI1radioactivity and radon exhalation rate from building materials, A knowledge 0[' Hldioactivity present in construction materials helps to (n) assess the possible radiological hazards to human health and (b) develop the standards and guidelines for use and management ofthe,~ materials. The pr~s~nt study deals with a total of 71 samples of II dilTerent commonly used structural and covering building materials in which, six types of covering/decorative building materials (marble, granite, mosaic stone, tiles, limestone and lime powder, where, most of them are imported from different countries); four types of structural building materials (cement, brick, sand and stone) and one by-product of coal-fired power plants (fly ash) were collected from varions manufactnrers ami suppliers to measure the natural radioactivity due to the presence of :!:!uRa,2J2.yhand 4rx.. The measurements were carried ont using gamma-ray spectrometry with an HPGe detector. The radon exhalation rate was measured by hermetically closing the sample in a contain~r and following the radon activity growth as a function of time. The specific activities of the different building materials srudied varied from 46.770101.91 to 117.770106.16 Bq.kg"l, 52.36:102.33 to 157.32"=8.55 Bq.k{l and 668,77="11.50 to 1463.3tli22.77 Bq.kg"1for 22liRa, m'lb and 4~, respectively. The results show that the lowest mean values of the specific activity of 226Ra,232Thand 4~K ar~ 46.77:101.91 (marble), 52.36:102.33 (marble) and 66~.77"=11.50 Bq.kg,1 (limestone), respectively while the highest mean values of the specific activity of the same radionuclides are 117.77"=6.16, 157.32"=8.55 and 1463.30"=22.77 8q.kg"l, respectively measured in fly ash. The measured activity concentrations for this radionuelide were compared with the reported data of other countries and with the typical world values. The average values of radon exhalution nlte of the studied materials varied li-om 0.010 to 0.044 Bq.kg'l.h'l. This study revealed that all the M f'itil'lltesis Abstract materials exhale radon with lower rate, in which some stone samples exhibit higher value than others. The potential radiological hazard associated with these building materials w~re estimated u~ing different approaches: th~ radium equivalent activities, external and internal hawrd indexes, the absorbed dose rate (outdoor and indoor) and the corresponding annual effective dose and gamma activity concentration index. The radium equivalent activities (Ra.q) ranged 'between 157 and 455.07 Bqkg.l, with two of the samples (fly ash and one Pakistani m<lrble-Onyx) exceeding the UNSCEAR reportcd recommended value of 370 Bqkg.l. The values of ~"l~rnal h<lzardindex (il",,) and the intenml radiation hazard index (Iim) associated with the natural rudionuclid~s range from 0.43 to 1.23 and 0.58 to 155, respectively. The values of Hex and Ii", arc less than WIity,in which four of the samples exceed this limit of unity. The mean indoor and outdoor absorbed dose rates were 164.05 nGy.h-1and 117.18 nGy.h-l, respectively, which is slightly higher than the population-weighted average of 84 nGy h.1 and 55 nGyXI respectively. The corresponding total annual effe<:tive dose rate and gamma activity concentration index was found to range from 0.60 to 1.68 mSv.}'1and from 059 to 1.67, respectively, in which five ofthc sample values exceed the dose criterion of I mSV.y"land 1 respectively. Applying dose criteria rceommend~d for building materials in the literature, all materials exc~ed the exemption annual dose criterion of 0.3 mSv y-I, nine of them m~et the upper dose limit of I mSv y-I and only two mat~rialsexceed this upper dose limit. The re~uJts show that some of the investigated building material samples exhibit higher values which clearly exceed the dose criterion of I mSv y-I (annual elTective dose rate) and 1 (gamma activity concentration index), r~spe<:tively,that arc set by various international organizations. Annual effective doses exceeding the dose criterion should be taken into account in tenns of radiation protection according to recoITllnendation 112 issued by the European Union in 1999. 'lhe above results suggest that thc usc of such materials in construction of dwellings or work places in Bangladesh is unlikely to give rise to any significant radiation exposure to thc occupants,