Background Radioactivity in the North West Province
Pule, Obusitse John
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The unavailability of the background radioactivity baseline data of the North West province for the various geological units is a problem from the radiation protection point of view. The regulation of the nuclear industry and the protection of members of the public against the harmful effects of ionising radiation requires this baseline data for appropriate regulating standards to be set. Hence this study has mainly focused on determining background radioactivity in various geological formations in terms of specific activity (Bq/kg) and dose rate (μSv/h) due to the external gamma radiation in order to make a contribution for regulatory purpose. The focus of this study was on the U-238 series due to its contribution on background, and thus the Ra-226 specific• activity was determined in Bqlkg. Gamma spectrometry units coupled to Nal(Tl) detectors were used both in-situ and in the laboratory to measure the gamma rays emitted from soil and dose rate was measured in-situ with electra G.M dose rate meter. The average background radioactivity from the measurements is high in granites, intermediate in shale and low in gabbro, norite anorthosites, quartzite calcrete with limestone, hybrid rocks, diabase and epidiorite and this pattern agreed with literature. The average radioactivity for the surveyed areas range from 26 Bq/kg to 150 Bq/kgfor various rocks types. The dose rate range from 0.15 μSv/h to 0.35 μSvlhfor various geological structures. The average specific activity is 150 Bq/kg and 82 Bq/kg in course grained and mixed granites, 72 Bq/kg and 61 Bq/kg in shale, polo and shale slate respectively. The average specific activity in norite, sandy soil, gabbro, norite anorthosite, brick clay and limestone is 37 Bq/kg, 25 Bq/kg, 28 Bq/kg, 26 Bq/kg and 27 Bq/kg respectively. The average dose rate range from 0.15 μSvlh to 0.35 μSv/h for various geological structures. There is a correlation of the results of this study with the studied geology in the North West Province. The results are also comparable with data from the previous international studies. There was a parallel study for Gauteng by the other worker. The geological formations that were surveyed in the North West Province are different from those surveyed in Gauteng Province. As a result the background radioactivity tends to be generally higher in Gauteng than the North West Province. The background radioactivity in most studied areas for both provinces should only be associated with NORM due to their distance from all TENO RM operations. Inferential statistics using student t-test indicate that there is 95 % probability that the background radioactivity mean for the North West Province lies in the interval 5 0. 048 Bq/kg to 61. 7./ Bq/kg. The average specific activity for the province is 55. 9 Bq/kg. The student t-value and the p-value, indicate that there is enough evidence to infer that the average specific activity for the whole North West Province is below 200 Bq/kg. The Nuclear Energy Act no. 131 of the CNS 1993 in South Africa, specifies the entry level into regulation of 200 Bq/kg for background specific activity. Any activity handling radioactivity material below 200 Bq/kg is not amenable for regulation because that is regarded to be background. From statistical analysis, all the areas that were covered by this study have a specific activity below a value of 200 Bq/kg. Hence the results suggest suggests that the entry level into regulation of 200 Bq/kg is appropriate because it does not bring areas at background level into regulation.