Gamma radiation measurements and dose rate in waste soil samples of OK-Tedi Gold – Copper mine in Western Province of Papua New Guinea

Abstract

The specific activity of natural radionuclides in the twelve different mining waste soil samples from OK Tedi gold -copper mine in Western Province of Papua New Guinea were analyzed to study the radiation effects in that region. The mean specific activities of 238U, 232Th, 40Kand 235U in the samples were found to range from 53.1 to 85.0 Bq/kg with an average value of 68.7+ 5.0 Bq/kg, 41.6 to 130.0 Bq/kg with an average value of 90.5+31.4 Bq/kg, 0.6 to 1.3 Bq/kg with an average value of 0.8 + 0.2 Bq/kg and 55.4 to 253.7 Bq/kg with an average value of 174.7+ 55.9 Bq/kg respectively. The concentrations of 238U and 232Th were found to be 5.6 and 22.2 ppm respectively which are greater than the world average values of 2.64 and 11.1 ppm. The Radium equivalent activity was calculated and ranges from 144.5 to 248.6 Bq/kg with average activity of 197.2 ± 39.2 Bq/kg. The absorbed dose rate was calculated for the samples and ranges from 64.40 Bq/kg to 109.90 Bq/kg with an average value of 86.4 ± 16.9 Bq/kg. The average annual indoor dose of 605.3 ± 118.3 μGy/yr and outdoor annual effective dose of 151.3 ± 29.6 μGy/yr was estimated. The external hazard indices were calculated and observed to vary from 0.4 to 0.7 with average value equal to 0.5 which is lower than the permissible value of 1.0. The internal hazard indices were found ranging from 0.6 to 0.7 with average value equal to 0.7 which is lower than permissible value of 1.0. The excess lifetime cancer risk (ELCR) was calculated using risk factors of International Commission on Radiological Protection and Biological Effects Ionizing Radiation and was found to range from 1.6x10-4 to 2.7x10-4 with an average value of 2.1x10-4 which is greater than the world average value of 1.45x10-4. Though the ELCR value is slightly greater, the radiation level in that region is less than the safe permissible level.