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The concentrations of naturally occurring radionuclides in the sediments of the Ogun River in Southwestern Nigeria were measured using NaI(Tl) gamma-ray spectrometry. The measurements were made in an effort to better understand the spatial distribution of natural radioactivity and to form a database of radioactivity levels of the Ogun River. The total average activity concentrations of (40)K, (226)Ra and (232)Th in the sediment samples representing the whole Ogun River from the upper region through the middle to the lower region of the river were 499.476±59.167, 12.649±3.476 and 11.774±5.126, respectively. The range of the activity concentrations of (40)K, (226)Ra and (232)Th for the Ogun River were found to be from 370.969±19.261 (at Olopade) to 608.023±24.658 (at Owere), 5.567±2.359 (at Ekerin) to 20.395±4.516 (at Sokori) and 5.037±2.244 (at Mile 12-Maidan) to 23.096±4.806 (at Sokori). The values obtained were compared with internationally accepted values. No man-made radionuclides were detected at any of the locations.

An indoor gamma dose rates survey was conducted in selected dwellings comprising homes and offices in Abeokuta, South Western Nigeria. Absorbed dose rates were measured using Gamma RAE II R (RAE Systems), which is a CsI-based dosimeter. Absorbed dose rates in the dwellings vary from 0.077 to 0.397 µSv/h, with an overall mean of 0.201 ± 0.074 µSv/h, which is more than twice the world population-weighted average indoor absorbed dose rate (0.084 µSv/h). Buildings made from mud bricks have higher absorbed dose rates than those made from cement-blocks, and houses built on rock outcrops have higher absorbed dose rates compared to those erected/built on soil. The calculated annual effective doses in the study area range from 0.540 to 2.782 mSv with an average value of 1.406 ± 0.521 mSv. The distributions of dose rates according to variations in the local geology and building materials were presented. This study provides data on the indoor component of the terrestrial gamma dose rates in Abeokuta, Nigeria, which is an update of the existing knowledge on the levels of the background radiation exposure in this high natural background radiation area. KEYWORDS Indoor gamma dose rates; Abeokuta; high background radiationCONTACT I. C. Okeyode

A radiation monitoring system comprising a Geiger-Muller counter connected to a smart phone via Bluetooth was used for a dose rate survey in some parts of south-western Nigeria. The smart phone has the Geographical Positioning System, which provides the navigation information and saves it along with the dose rate data. A large number of data points was obtained that shows the dose rate distribution within the region. The results show that the ambient dose rates in the region range from 60 to 520 nSv -1 and showed a bias that is attributable to the influence of geology on the ambient radiation dose in the region. The geology influence was demonstrated by superimposing the dose rate plot and the geological map of the area. The potential applications of the device in determining baseline information and in area monitoring, e.g. for lost or abandoned sources, radioactive materials stockpiles, etc., were discussed in the article, particularly against the background of Nigeria's plan to develop its nuclear power program.

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