Gamma-ray absorbing characteristic of obsidian rocks as a potential material for radiation protection

Abstract

In this study, natural radionuclide levels and mass absorption coefficients of obsidian samples were examined to determine their gamma radiation properties. Fourteen obsidian samples were collected from 7 different locations in Rize province, İkizdere region, Turkey. X-ray fluorescence measurements of the samples revealed the silica structure and comparable elemental structure with slight differences in atomic ratios. Radionuclide analysis showed that the 137Cs activity was below the detection limit, and the mean activities of 238U, 232Th and 40K were 93 ± 9, 67 ± 7, 1027 ± 19 Bq.kg−1, respectively. The average experimental mass absorption coefficients at 81.0 keV, 302.9 keV, 356.0 keV and 661.7 keV were found to be 0.216, 0.108, 0.098 and 0.080 cm2 g−1, respectively. In the <100 keV region which the photoelectric effect is dominant, differences among the absorption coefficients were more pronounced, while it was relatively much smaller in the intermediate energy region. Also, it was seen that the absorption coefficients of the samples were higher than many materials, especially in the low energy region. The average half-value thicknesses showed that obsidian between 1.43 cm and 3.84 cm depending on the photon energy should be used to halve the radiation intensity. In addition, it was determined that the thicknesses in the range of 4.75 cm–12.76 cm were sufficient to reduce the intensity to one tenth. Considering all the analysis results, it can be said that obsidian is a potential material in radiation protection and its absorption properties can be improved by processes such as elemental doping.