Radiological Risk of Building Materials Using Homemade Airtight Radon Chamber

摘要

Soil based building materials known to contain various amounts of natural radionuclide mainly ~(238)U and ~(232)Th series and ~(40)K. In general most individuals spend 80 % of their time indoors and the natural radioactivity in building materials is a main source of indoor radiation exposure. The internal exposure due to building materials in dwellings and workplaces is mainly caused by the activity concentrations of short lived ~(222)Radon and its progenies which arise from the decay of ~(226)Ra. In this study, the indoor radon concentration emanating from cement brick, red-clay brick, gravel aggregate and Portland cement samples were measured in a homemade airtight radon chamber using continuous radon monitor 1029 model of Sun Nuclear. Radon monitor were left in the chamber for 96 hours with an hour counting time interval. From the result, the indoor radon concentrations for cement brick, red-clay brick, gravel aggregate and Portland cement samples determined were 396 Bq m~(-3), 192 Bq m~(-3), 176 Bq m~(-3) and 28 Bq m~(-3), respectively. The result indicates that the radon concentration in the studied building materials have more than 100 Bq m-3 i.e. higher than the WHO action level except for Portland cement sample. The calculated annual effective dose for cement brick, red-clay brick, gravel aggregate and Portland cement samples were determined to be 10 mSv y~(-1), 4.85 mSv y~(-1), 4.44 mSv y~(-1) and 0.72 mSv y~(-1), respectively. This study showed that all the calculated effective doses generated from indoor radon to dwellers or workers were in the range of limit recommended ICRP action levels i.e. 3 - 10 mSv y-1. As consequences, the radiological risk for the dwellers in terms of fatal lifetime cancer risk per million for cement brick, red-clay brick, gravel aggregate and Portland cement were calculated to be 550, 267, 244 and 40 persons respectively.