Ionizing Radiation Dose to the Skin Assessed after Rapid Detection of 232Th in Consumer Products.

Abstract: After some consumer products indicated elevated levels of 232Th progeny by gamma-ray spectrometry, a microwave digestion and inductively coupled plasma-mass spectrometry (ICP-MS) procedure was implemented for the direct assay of 232Th content to ensure compliance with Federal regulations and guidelines. Levels of 232Th were determined by ICP-MS based on standard calibration using a 205Tl internal standard. The method had a method detection limit (MDL) of 0.15 Bq g-1 and a lower limit of quantification (LLOQ) of 0.65 Bq g-1 for 232Th, making it a suitable confirmatory method following gamma-ray spectrometry. The 232Th activity concentration calculated from the ICP-MS results ranged from 2.0-3.4 Bq g-1 for the kinesiology tape samples and 20 Bq g-1 for the silicone ion bracelet. The VARSKIN+1.0 software program was used to calculate the shallow dose equivalent of ionizing radiation from 232Th and its progeny from the ICP-MS results. The skin dose to the consumer wearing the kinesiology tape ranged from 0.48-1.6 mSv y-1. The skin dose to the consumer with constant wear of the silicone ion bracelet was estimated to be 17 mSv y-1. Although 232Th may be determined indirectly by assay of high abundance gamma rays produced by its progeny, the US Code of Federal Regulations (CFR) requires the direct assay of 232Th for confirmatory analysis. We found this ICP-MS method to be a rapid 232Th confirmatory technique compared to a chemical separation followed by alpha spectrometry procedure.