Development and application of an analytical strategy for the determination of ²³²Th and ²²⁸Th in ivory based on the combined use of inductively coupled plasma mass spectrometry and α-spectrometry

Andreas Schmidberger
In this work, the significance of the determination of the ratio of the activity concentrations of 228Th and 232Th in the context of age determination of ivory was discussed and the corresponding dating uncertainty was reduced. Calibration curves for the relevant isotopes for ivory dating, namely 14C, 90Sr and 228Th/232Th, were created by analyzing young ivory samples with known age. It was shown that the age determination of ivory via the thorium isotopes will become an indispensable and
more » ... ul technique in the future. The applicability of the bomb curve dating via the isotopes 14C and 90Sr will fade, due to ambitious findings for ivory, which will be poached within the future. Since the ratio 228Th/232Th is not affected by the atomic bomb tests in the sixties, unlike the isotopes 14C an 90Sr, the age determination via 228Th/232Th will also work in the future and the method will be able to identify illegal ivory, which is not older than 40 years. The validation of the created time-depending calibration curve of 228Th/232Th in ivory was done by repeated analysis of the same ivory samples with known age after half a year and by repeated analysis of an ivory sample within two years. The expected trend of the ratio change could be confirmed by these experiments. The activity concentration ratio 228Th/232Th rises after death of the elephant, reaches a maximum after roughly four years, decreases and assimilates to a value of one after 40 years. The uncertainty of the overall 228Th/232Th determination could be reduced by developing improved strategies for the determination of the 228Th and 232Th activities. 232Th showed low counting rates and high uncertainties for the determination via α-spectrometry, but 232Th was well accessible via inductively coupled plasma mass spectrometry (ICP-MS). An ICP-MS measurement was integrated in the common analytical procedure. The approach was validated by the analysis of 232Th standard solutions as well as ivory samples. It was shown that the ICP-MS and the α-spectrometry provided [...]
doi:10.5283/epub.40457 fatcat:h3lcdskze5dr3dmpgqjtmd6kza