Masters Degrees (Physics)
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Browsing Masters Degrees (Physics) by Author "Bailey, Tarryn"
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- ItemNatural radioactivity in soils of Ijero, Nigeria: measurements and risk assessment(Stellenbosch : Stellenbosch University, 2019-12) Bailey, Tarryn; Newman, Richard T.; Maleka, P. P.; Stellenbosch University. Faculty of Science. Dept. of Physics.ENGLISH ABSTRACT: Several soil samples were obtained from Ijero, Nigeria, where the chemical and radio-toxicity of soil is under question due to ongoing and unregulated mining activities. The soil samples were crushed, sieved, dried and sealed in identical cylindrical containers. The activity concentrations of primordial radionuclides in the 238U series, 232Th series and 40K were measured using a High-Purity Germanium (HPGe) detector. Subsequently, radiological risk factors were calculated to assess the average risk to an individual living in Ijero. The measured activity concentrations for the 238U series ranged from 10.1 1.4 to 83.9 2.1 Bq/kg with a mean value of 38.5 Bq/kg. For the 232Th series, the activity concentrations ranged from 11.3 2.9 to 108.0 2.4 Bq/kg with a mean value of 37.1 Bq/kg. Finally, the 40K activity concentration ranged from 67 26 to 1196 36 Bq/kg with a mean value of 461 Bq/kg. The mean values for the activity concentrations of the 238U series, 232Th series and 40K were comparable to the global population-weighted average for concentration in soils, given by UNSCEAR 2000, of 33 Bq/kg, 45 Bq/kg and 420 Bq/kg respectively. In total, thirty soil samples from Nigeria were measured. Of these samples, thirteen had 238U series concentrations above 33 Bq/kg, three of those samples had activity concentrations for the 238U series above 70 Bq/kg. For the 232Th series, thirteen samples had activity concentrations above 45 Bq/kg with two samples above 90 Bq/kg. Finally, seventeen samples had 40K activity concentrations above 420 Bq/kg with eleven of those above 800 Bq/kg. Five soil samples had hazard indices that summed to more than the permissible limit of 1 mSv/yr. Eight samples were above the permissible limit for the Annual E ective Dose rate, where indoor and outdoor dose rates must sum to 1 mSv/yr. The Annual Gonadal Equivalent Dose limit of 300 Sv/yr was surpassed by twenty- ve samples. For the Excess Lifetime Cancer Risk (ELCR) and excess percentage risk, which estimates the probability that an individual could develop cancer in their lifetime, seven samples exceeded the maximum ELCR of 0:29 103. The ELCR results ranged from 0:102 103 to 0:483 103. The highest ELCR result is 1.67 times greater than the upper recommended value of 0:29 103. A value of 1.67 for the ratio of the calculated ELCR to the maximum permissible ELCR corresponds to an excess percentage risk of 67%. The mean ELCR is 0:239 103 which is below the maximum recommended value. There are certain locations where the activity concentration of primordial radionuclides is high, far surpassing the world average. However, most of the soil samples measured did not exceed the recommended maxima for activity concentrations and radiological risk factors.