Decay counting in the age of AMS

Up to the advent of AMS, all the accomplishments of 14C dating, and the studies of 10Be and other long-lived radionuclides, were made by low-level decay counting, the technique pioneered by W.F. Libby. It will hardly be news to people at this conference that, while much was accomplished in the three decades when counting prevailed, the world has now changed decisively. I will try to give an account of where low-level counting was 'before the revolution', and of what its usefulness is today. There are still some remarkable examples of its application, the best being the neutrino experiment of Raymond Davis, and its potential successors. Some cosmogenic nuclides, whose half-lives are less than 103 yr, are still best measured by decay; this will continue unless the overall ion yield of AMS systems rises markedly from present levels. One long-lived nuclide, 53Mn, is still best measured by neutron activation as 312-day 54Mn, but this may not continue. (orig.)