Natural Radionuclide Contents in Ceramic Clays in Southern Thailand and their Radiation Hazard Indices

Abstract

The present study aimed to: 1) measure the natural radioactivity due to the presence of radionuclides in natural clay, used widely as raw material in the ceramics industry; and 2) assess the possible radiological hazard associated with the ceramic products made with them. Natural clays from 17 localities in southern Thailand and commercial clay used in ceramics and pottery factories were studied. The activity concentrations of natural radionuclides, Th-232, Ra-226 and K-40, were measured by means of low background gamma-ray spectroscopy with a high purity germanium detector. The measured activity concentrations of Th-232, Ra-226 and K-40 of all clay samples ranged from 83 to 476, 67 to 576 and 161 to 1200 Bq/kg, respectively. These levels were comparable to those of other clays globally. The calculated radium equivalents varied from 327 to 1226 Bq/kg, with the average value (662 Bq/kg) being significantly higher than the standard criterion of 370 Bq/kg. The external hazard indices varied from 0.88 to 3.31, with an average of 1.79, which was higher than the standard criterion (1). The gamma radiation hazard indices of all samples studied ranged from 1.14 to 4.22, which were below the criterion limit (< 6) corresponding to a dose rate <1 mSv/y for superficial use and use with other materials with restricted use, but were higher than the criterion limit (1) when used in bulk amounts. Therefore, the hazard indices should be reduced by choosing carefully among the clays studied and other mixing ingredients.