Occurrence of natural radionuclides and fallout cesium-137 in dry-season agricultural land of South Western Nigeria

The radioactivity of the Opa river - irrigated farmlands in the south western Nigeria was determined using an HpGe based, low-level passive gamma-counting system. With the exception of two isotopes, the main radionuclides analysed in the sample were the progenies of 238U and 232Th. The other two isotopes were the naturally occurring 40K and the anthropogenic 137Cs. The result obtained showed elevated levels of radioactivity from all detected radionuclides compared to the published data for this area. Enhanced levels of naturally occurring radionuclides is attributed to the use of phosphatic fertilizers for dry season vegetable cultivation along this river banks. The presence of the fission product 137Cs could be traced to the fallouts occasioned by the various French nuclear tests in the Sahara desert, and probably, some effect of the more recent nuclear reactor accident at Chernobyl in 1986. (author)