Outdoor external doses in the high background radiation areas of Lambwe east location in southwestern Kenya

Abstract

Soils and rocks from a number of areas underlied by carbonatite rocks in Kenya have been associated with high radioactivity. A study, comprising background radiation measurements, and radioecological and health surveys in some of these areas was initiated recently. In this paper we provide a preliminary result of the background radiation measurements carried out in three areas: Ruri, Kuge and Sokolo in the Lambwe east location of Suba district, southwestern Kenya. These areas are roughly between latitudes 0˚30’S and 1˚00’S, bounded on the east by longitude 34˚30’E and on the west by the shores of Lake Victoria and the Kavirondo gulf. Altitudes range from about 1000 m on the shores of Lake Victoria to above 1800 m on top of the Ruri hills. Absorbed dose rates in outdoor air in the areas were measured using survey meters. The values range from 614 to 6000 nGyh-1 with an overall mean of 2106 nGyh-1. Gamma-ray spectrometric analyses of samples of soils and rocks were also carried out using high-purity germanium (HPGe) detector. The mean activity concentrations in the samples are 1215 Bqkg-1; 123 Bqkg-1 and 511 Bqkg-1 for 232Th, 226Ra, and 40K, respectively. The results show that external doses in air in these areas are many times higher than in the normal background radiation areas. The main contribution is from the naturally occurring radionuclides in the soils and rocks, particularly those associated with carbonatites, but it was also found that the contribution from Cosmic rays is enhanced at these altitudes.