Validation of Gamma Ray spectrometry process used to determine the Radionuclides and radioactivity levels in decorative granite countertops.
Maibane, Kutullo Freedom
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Humans are continuously exposed to low level of ionizing radiation, sources include soil, medical treatment and as well as radiation emissions from natural materials like granite rocks. The radiation levels present in these granite rocks varies depending on the mineral properties and their origins. The aim of this study is to assess the radiation levels in various granite countertops available commercially in South Africa. The radiation levels present in the granite countertop samples were determined using the available low-background HPGe gamma-ray detector system at iThemba LABS. Initially, the study focused on the optimisation of the photopeak efficiencies of the detector system to match the samples, i.e. 'box-like' geometry as opposed to the traditionally used Marinelli beaker geometry. A soil sample with known activity (238U series: 940 30 Bq/kg; 232Th series: 660 20 Bq/kg and 40K: 153 8 Bq/kg) determined with Marinelli beaker geometry was used to prepare an artificial reference material for the new box geometry. The new-efficiency parameters determined were used to calculate the activity concentrations present in the 5 granite countertop samples. The range of activity concentration levels determined in all granite counter samples are 3 +- 610 Bq/kg, 50 +- 170 Bq/kg and 1400 +- 2000 Bq/kg for 238U, 232Th and 40K, respectively. These levels are higher than the world mean values reported by UNSCEAR of 40 Bq/kg, 40 Bq/kg and 370 Bq/kg for 238U (2 samples), 232Th (4 samples) and 40K (all samples), respectively. The estimated absorbed dose rates range from 194(4) to 790(30) nGy/h. The radionuclides 226Ra, 232Th and 40K contributes approximately 44%, 52% and 4%, respectively, of the total absorbed dose rate in all granite countertop samples.