Evaluation of potential radiological hazards of unfired construction materials containing fly ash in Vietnam

In this study, the specific activities of ²²⁶Ra, ²³²Th and ⁴⁰K in the unfired construction materials (solid card bricks, 4-hole bricks, pavement bricks) containing fly ash and bottom ash from a coal-fired thermal power plant in Vietnam were measured using the low-level gamma-ray spectrometer with HPGe detector. Also, the ²²²Rn concentrations in these materials were analyzed using RAD7 radon monitor and then radon mass exhalation rate and emanation fraction of these materials were calculated. The potential radiological hazards for residents living in the model room made of these materials were evaluated. The average specific activity of ²²⁶Ra, ²³²Th and ⁴⁰K were found as 67.7, 79.3 and 703.5 Bq kg^-1, respectively. The total annual effective dose (due to external gamma exposure and internal radon exposure for resident living in the CEN model room made of the unfired brick samples) was found as 0.9 mSv y^-1 which is lower than the worldwide average dose of 2.4 mSv y^-1. Calculations from ResRad-Build code showed that the doses due to radon exposure account for from 62.3% (at the first year) to 98.8% (at the next 30 years) of the total gamma and radon dose. Under low air exchange to the outside environment, from the 6th year onwards, the total dose may exceed the average dose value from natural radiation exposure sources.