Gamma ray spectrometric analysis on surface soils around Mrima Hill, Kenya using Nal(TI) detector and decomposition technology

Abstract

The activity concentrations of naturally occurring radionuclides in surface soils around Mrima hill in the Kenyan coast have been measured using NaI(TI) gamma ray spectrometer. Mrima hill is under lied by carbonatite rocks which are associated with high natural background radioactivity. In order to minimize errors in the measurements, the gamma ray spectral data was systematically analysed using the decomposition method. The average concentrations of 238U, 232Th and 40K in the samples are 207.03±11.3 BgKg -1, 500.7±20.3 BgKg-1 and 805.4±20.7 BgKg-1 respectively. It is observed that the activity concentrations are above the global average values. As a measure of radiation hazard to the general public, the absorbed dose rate in air at a height of 1m above the ground surface was estimated. The calculated radiation absorbed dose from the different sampling points, ranges from 253.8±2.5nGyh-1 to 733.1±3.4nGyh-1 with an average of 440.7±16.8 nGyh-1. This value is higher than the worldwide average of 60 nGyh" '.The annual outdoor effective dose ranges from 0.64 mSvy-1 to 1.85 mSvy-1 with an average of 1.11mSvy-1. Further studies on radionuclide concentrations in water and biota and numerical modeling of vertical distribution of radionuclides concentrations in soil are suggested for estimation of risks associated with natural radioactivity.