Potential of gamma-ray spectrum analysis as a method to determine radioactive elements in geological samples
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Date
2016-11-05
Authors
Waniganeththi, W.S.
Wijayawardane, R.L.
Journal Title
Journal ISSN
Volume Title
Publisher
University of Peradeniya, Sri Lanka
Abstract
Natural gamma-ray spectrometry can be used to measure the activity of Potassium-40( ⁴⁰K), Uranium-238 (²³⁸U) and Thorium-232 (²³² Th) in geological samples. The knowledge of activity of ⁴⁰ K, ²³⁸ U and ²³² Th can be used to determine the concentration of respective elements present in the sample. In this research rock and soil samples were collected from various geological locations, which were suspected as radioactive mineral bearing samples. X- ray florescence analysis was carried out to take a rough idea about the elements present in the sample. A thorium rich sample was selected for further analysis. The rock sample was crushed and completely filled to the standard cylindrical geometry. It was weighted and sealed such that radon gas would not escape from the sample. The Sodium Iodide (NaI) detector set up available in the nuclear physics laboratory, Department of Physics was used to obtain the gamma-ray spectrum. Sample was analyzed for two hours. For room background subtraction, background spectrum was obtained for the same time with no source in front of the detector. The gamma-ray spectrum analyzed by Genie 2000 software was used to determine ²³² Th wt. %. Then the sample was analyzed by High purity Germanium (HpGe) detector model BE5030 in the Nuclear Analytical Laboratory, Life Science Division, Atomic Energy Board. The sample was analyzed with respect to standard samples obtained from Analytical Quality Control Service of the International Atomic Energy Agency. The three standards of ⁴⁰ K, ²³⁸ U and ²³² Th were prepared according to same geometry of the sample. The gamma ray spectra of sample and three standards were used to determine ²³² Th wt. %. The HpGe detector analysis confirmed that ²³² Th wt. % is 2.5 on average. The same average ²³²Th wt. % value was obtained from NaI detector analysis, considering 2615 keV and 911 keV peaks. Therefore, it can be suggested that 2615 keV and 911 keV are the best peak for ²³² Th detection. Furthermore, it can be confirmed that the NaI detector is still capable of analyzing samples accurately up to International Atomic Energy Agency (IAEA) standards.
Description
Keywords
Gamma-ray spectrometry , Radioactive elements , International Atomic Energy Agency (IAEA)
Citation
Proceedings of the Peradeniya University International Research Sessions (iPURSE) – 2016, University of Peradeniya, P 351