Contributions of ²³⁸U, ²³²Th, and ⁴⁰K to the radiogenic heat production in selected river sediment samples of South Africa

Abstract

In this study, 16 sediment samples were collected from Bree, Klein-Brak, Bakens and uMngeni rivers of South Africa and were prepared, analysed and evaluated for the activity concentration of ²³⁸U, ²³²Th and ⁴⁰K concerning its radiogenic heat production using a high-purity germanium detector. The results show that ²³⁸U is the prevalent radionuclide in radiogenic heat production, with ²³²Th and ⁴⁰K emerging as trace elements. The mean activity concentrations are 28.97%, 63.69% and 7.34% for uranium, thorium and potassium, respectively, from all sampling locations. This shows that a high radioactive concentration of a specific radionuclide does not necessarily imply its increased contribution to radiogenic heat production. The radionuclide contributions to radiogenic heat production at all sampled locations are 59.39%, 35.11% and 5.50% for uranium, thorium and potassium, respectively. The mean radiogenic heat production rate in the study area ranged from 0.0180 $\mathrm{\mu W}{m}^{-3}$ in sediment samples from the Bree River in Western Cape to 0.0072 $\mathrm{\mu W}{m}^{-3}$ in sediment samples of uMgeni River in KwaZulu-Natal. All values obtained for this study are five times lower than the average continental radiogenic heat production of 1 $\mathrm{\mu W}{m}^{-3}$. This study provides insight into the radiogenic heat production rate due to the presence of radionuclides in all river samples.

Keywords:

• concentration
• HpGe detector
• natural radionuclides
• radiogenic heat
• river sediments

ACKNOWLEDGMENT

The authors are grateful to iThemba LABS, Capetown, South Africa, for giving us access to their Environmental Research Laboratory for measuring the radioactivity levels in the sediment samples.