Study of radon exhalation from soil to ascertain the elevated levels of background radiation of Bangladesh

¹ Radioactivity Testing and Monitoring Laboratory, Bangladesh Atomic Energy Commission, P.O. Box 1352, Chittagong, Bangladesh
² Department of Physics, University of Chittagong, Chittagtong, Bangladesh

Abstract

The outdoor environmental background radiation level in normal area of Bangladesh ranged between 110 and 445 nGy.h^-1 was observed in a countrywide background radiation survey using β-γ radiation survey meter. The United Nation Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) reported to the united Nations General Assembly in its 1988 report that the outdoor country averaged environmental background radiation level in air in 23 countries representing about one half of the world population were found to range between 24 and 85 nGy.h^-1, with a mean value of 55 nGy.h^-1, which is one fourth of the radiation dose level of Bangladesh. In the present study, activity concentration of radium and radon radionuclides was measured in the soil samples of the country and measured their radon emanation coefficient, and radon mass exhalation and radon area exhalation rates with an aim to evaluate the cause of high background radiation level in Bangladesh. The result shows that the concentration of ²²⁶Ra in most of the soil samples was higher than that of world average value, and the concentration of ²²⁴Ra, a daughter of ²³²Th-series, is more than two times higher than the world average value. The activity of ⁴⁰K was found higher than both the range and average world value in most of the samples. The results of ²²²Rn emanation coefficients, ²²²Rn mass and area exhalation rates are very significant. Values of radon emanation coefficients for the soil samples in a number of locations were found in excess of world average value. The ²²²Rn emanation coefficients was found in the range 3.10 - 44.68 %, the mass exhalation rates was found in the range 2.50 - 27.84 µBq.kg^-1.sec^-1, and the area exhalation rates was found in the range 3.15 - 38.15 mBq.m^-2.sec^-1. Due to high concentrations of radium and potassium in soil and the high radon exhalation rate the external and internal doses are also higher. The total external dose from soil was found higher than the reported results of most of the countries of the World. This result would be helpful to assess the radiation exposure to human, animal and plants, and radiation related cancer risk.