Natural Radioactivity Concentration And Effective Dose Rate From Jos Tin Mining Dumpsites In Rayfield, Nigeria

Abstract

The International Commission on Radiological Protection (ICRP) has recommended the annual effective dose equivalent limit of 1mSvy^-1for the individual members of the public and 20mSvy^-1 for the radiation workers. The assessment of naturally occurring radio nuclides ²²⁶Ra, ²³²Th and ⁴⁰K in nine major tin mine dumpsites in and closely around Rayfield area of Jos Plateau were carried out using gamma-ray spectrometry with NaI(Tl) detector to determine the natural radio nuclide in the dumpsites and to evaluate the hazards these might have on the public. The calculated average activity concentration of ²²⁶Ra, ²³²Th and ⁴⁰K in the samples were 132.6±21.4, 351.4±20.9 and 319.6±37.7 Bqkg^-1 respectively. The mean activity concentration of ²²⁶Ra and ²³²Th in the present study is much higher than the world-wide average values of 33 Bqkg^-1 and 45 Bqkg^-1 respectively but the mean concentration of ⁴⁰K is lower compared to the world average of 420 Bqkg^-1.

The present study revealed that the calculated average absorbed dose rate, radium equivalent dose, indoor annual effective dose rate and outdoor annual effective dose were found as 293.27nGyh^-1, 569.68mSvy^-1, 1.44mSvy^-1 and 0.34mSvy^-1 respectively. The mean values of the absorbed dose rate, radium equivalent dose and the indoor annual effective dose rate are much higher than the world average recommended safety limits. Therefore it can be concluded that the present study area is radiologically unsafe from radiological hazards and will pose harmful effects to the environmental and the living population. However, no significant radiological impact have been observed on the surrounding environment and the living population, this might be attributed to the higher value of the Nigeria annual effective dose of 0.098 mSvy^-1 compared to the world annual effective dose of 0.07mSvy^-1.

Keywords: Radioactivity, Effective dose, Tin mining, Dumpsites.