Assessment of radioactivity levels in coal, coal ash and soil in Kiwira coal mine using gamma-ray spectrometry

The extent of natural radioactivity in coal mined in Tanzania is still unknown since no studies have been conducted. Few studies have been conducted on exposure to respirable dust and concentration of heavy metals. This study is aimed to assess the radioactivity levels and associated dose rates from the naturally occurring radionuclides 226Ra, 232Th and 40K in coal, coal ashes and soil at Kiwira coal mine by gamma ray spectrometry. A total 51 representative coals, fly ash, bottom ash and soil samples were analysed and the radioactivity was measured using gamma-ray spectrometer for a counting time of 10 hr for each sample. From the measured spectra, activity concentrations were determined for 226Ra, 232Th and 40K. The mean 226Ra activity concentration in coal, fly ash, bottom ash and soil were measured as 413 ± 26, 448 ± 33, 429 ± 12 and 378 ± 22 Bqkg-1 respectively. The mean232Th activity concentration in coal, fly ash, bottom ash and soil were measured as 372 ± 36, 455 ± 14, 438 ± 15 and 331 ± 32 Bqkg-1 respectively. The mean 40K activity concentration in coal, fly ash, bottom ash and soil were found to be 2930 ± 433, 3069 ± 358, 3299 ± 109 and 2632 ± 50 Bqkg-1 respectively. These concentrations were higher by several orders of magnitude than the worldwide average values. The calculated radium equivalent activity, absorbed dose rate, external hazard index and the average annual effective dose rate in fly ash (1335 ± 60 Bqkg-1, 610 ± 29 nGyh-1, 4 ± 0.4, 738 ± 52 µSvy-1) bottom ash (1310 ± 35 Bqkg-1, 601 ± 16 nGyh-1, 4 ± 0.4, 737 ± 20 µSvy-1) and soil (1053 ± 63 Bqkg-1, 484 ± 27 nGyh-1, 3, 594 ± 33 µSvy-1) were higher by 361%, 1070% 400% and 1054% than the international recommended values. The results of the current study highlight the severity of the radiological hazards of the workers and public in the vicinity of Kiwira coal