Estimation of radiation doses associated with natural radioactivity in sand samples of the north western areas of Pakistan using Monte Carlo simulation

Summary Activity concentrations of naturally occurring radionuclides, i.e., ²²⁶Ra, ²³²Th and ⁴⁰K, were measured in sand samples of north western areas of Pakistan using gamma-spectrometry. The measured ranges of activity concentrations for ²²⁶Ra, ²³² Th and ⁴⁰K were 36.9-51.9, 52.5-67.6 and 680-784 Bq ^. kg^-1, respectively. Associated external dose was calculated using Monte Carlo simulation technique. A theoretical model to determine the gamma dose rate at 1 m height from the sand was employed for calculation the mass attenuation coefficient and self absorption in sand slab for the gamma-energies of these radionuclides and their progeny. The weighted average values of the measured gamma dose rates were 3.3, 4.5 and 12.4 nGyh^-1 for ²²⁶Ra, ²³² Th and ⁴⁰K, respectively, with effective dose of 0.022±0.004 mSv ^. y^-1. Monte Carlo simulation shows that the sand slabs having more than 15 cm effective thickness contribute very little to the external gamma dose rate. The values of the external dose rate and annual effective dose were found to be much lower than the world average as well as from other countries of the world.