First results on radiometric dating of metals by alpha spectrometry

A new TSAC (Thick Source Alpha Particle Counting spectrometry) setup of high geometrical efficiency and low intrinsic background was built to measure the alpha particles coming from the 238U and 232Th decay chains radionuclides with concentrations down to the ppm level. It was designed to test the 226Ra/230Th method, which is the only direct metal dating method proposed to date. Micro-PIXE, micro-RBS and SEM-EDS were used as complementary analytical techniques in order to search for heterogeneities and/or impurities that could bias the TSAC data. Ores, resulting slags and metallic prills from two recent smelting experiments that reproduced ancient techniques and two ancient coins were studied to determine how radionuclides fractionation occurs during smelting. With this TSAC setup the background signal was extremely low, but comparable to the signal from the measured metals. Preliminary results show no evidence of a preferential depletion of 226Ra in a melted metal with respect to the other radionuclides. © 2015 Elsevier B.V.