Applying in-Situ and Laboratory-based Gamma Spectrometry to Determine Activity Concentration and Distribution of 40 K, 226 Ra and 232 Th in Abeokuta, Southwest Nigeria

Abstract

The applications of radionuclides are potential sources of health risk and also a concern in the area of nuclear security. It is therefore imperative to determine the presence of the different radionuclides present in the environment at all times, because it is necessary
to control and assess the risk level in the environment. The present study compares activity concentrations of the primordial radionuclides ⁴⁰K,²²⁶Ra and ²³²Th obtained from laboratory gamma spectrometry measurements with the activity concentration s of the radionuclides as obtained from in-situ measurements. Soil samples were randomly collected from nineteen different points within Abeokuta city ensuring good coverage of the city area. A mobile gamma spectrometry system was used to collect gamma spectra
measurements in the field. The obtained values are presented. The ranges of activity concentrations for ⁴⁰K, ²²⁶Ra and ²³²Th have been found to be 113 – 1975, 5 – 128 and 181– 3284 Bqkg^-1, respectively for laboratory gamma spectrometry and 104 – 1312, 31 – 121
and 104 – 2578 Bqkg^-1, respectively for in-situ gamma spectrometry measurements. This study showed that the average activity concentrations of the primordial radionuclides in Abeokuta were much higher than worldwide averages of 400, 35 and 30 Bqkg^-1
for ⁴⁰K, ²²⁶Ra and ²³²Th, respectively. From both methods,²³²Th is seen to be the major contributor to the environmental radioactivity of Abeokuta. Good correlations also were deduced between the activity concentration results obtained from laboratory and in-situ gamma spectrometry , which therefore implies a significant relationship between the two methods used in the study.

Keywords: In-situ gamma, Gamma spectrometry, Activity concentration, Radionuclides.