Determination of natural radioactivity in beach sand in the extreme south of Bahia, Brazil, using gamma spectrometry

Abstract

The natural radionuclides activity concentrations in beach sand of the extreme south of Bahia, Brazil, was measured by Gamma Spectrometry. The Radium Equivalent Activity, the external hazard index, the absorbed dose rate and the annual effective dose were assessed and compared with internationally published values for external dose and activity concentrations. The activity concentrations of 226 Ra, 232 Th and 40 K in beach sand ranged from 8.4 to 8,300 Bqkg -1 with a mean value of 910 Bq.kg -1 , from 21 to 18,450 Bqkg -1 with a mean value of 2,220 Bqkg -1 and from 3.4 to 3,110 Bqkg -1 with a mean value of 352 Bqkg -1 , respectively. The results indicate that the absorbed dose rates range from 21 to 14,450 nGyh -1 with mean value of 1,792 nGy.h -1 . The highest value of gamma dose rates among the studied beaches were found in Cumuruxatiba (14,450 nGyh -1 ). The annual effective dose range between 0.03 and 17.70 mSvy -1 , with the mean value of 2.20 mSvy -1 . In four studied beaches, the assessed outdoor annual effective doses are above the worldwide average of 0.07 mSvy -1 as reported by the United Nations Scientific Committee on the Effects of Atomic Radiation. Especially in the area of black sands, a big part of Cumuruxatiba beach, whose annual effective dose of 17.70 mSvy -1 is much higher than worldwide average.