Calculation of dose rate conversion factors for ²³⁸U, ²³²Th and ⁴⁰K in concrete structures of various dimensions, with application to Niš, Serbia

Abstract

The absorbed gamma dose rate in indoor air due to natural radionuclides in concrete as a building material was determined in this work. The dose rate conversion factors for 238U, 232Th and 40K, for standard rooms as well as rooms with different sets of dimensions, were evaluated by the point kernel technique, using Harima (geometric progression) build-up factors. The values of the conversion factors, in units (nGy h-1 (Bq kg. -1)-1) calculated for the standard room are: 0.76, 0.91 and 0.070, respectively for 238U, 232Th and 40K. The fitting formula was obtained for dose rate conversion factors, enabling them to be conveniently calculated for a room with arbitrary dimensions. For concrete block samples collected in the area of Niš, Serbia, the measurement of the radionuclide activity concentrations was also carried out. The evaluated absorbed dose rate conversion factors were then applied in the assessment of corresponding indoor gamma dose rates, finding that all the concrete samples fulfilled the usage requirement. © The Author 2012. Published by Oxford University Press. All rights reserved.