Absolute Measurements and AMS – Towards the redetermination of the half-life of ³²Si
Matthias Schlomberg1, Dr Christof Vockenhuber1, Hans-Arno Synal1, Dorothea Schumann2, Mario Veicht2, Ionut Mihalcea2, Anton Wallner3
1ETH Zurich, , Switzerland, 2PSI, , Switzerland, 3HZDR/ANU, , Australia
AMS usually relies on relative measurements, i.e., measurements of unknown isotopic ratios of samples relative to well-known standard materials. In the case of ³²Si no such standard material is available; even worse its half-life of about 150 years is still not well known despite several independent measurements over the past decades.
The determination of the half-life of long-lived radionuclides requires two absolute measurements, the activity concentration (Bq/g) and the atom concentration (at/g) of the radionuclide, respectively, both having their own challenges and can result in (often unknown) systematic errors. In the past, AMS has been used for the latter, however, given the complex AMS instrument these measurements require some extra effort. All relevant changes to the measured isotopic ratios must be well understood. In particular fractionation effects in the ion source and during the stripping process in the tandem accelerator can have a significant effect especially at large mass differences. These can be monitored with stable isotopes, luckily silicon has three stable isotopes, ²⁸Si, ²⁹Si and ³⁰Si. Additionally, losses to the radionuclide in the detection setup must be quantified. We aim for a simple absorber setup for isobar separation of ³²Si from ³²S, details are presented in another contribution to this conference.
In this presentation, we concentrate on the challenges of the absolute measurement of ³²Si for the half-life measurement within the SINCHRON collaboration with partners from PSI, CHUV, PTB, ANU and ETH. Results of dedicated charge state distribution measurements and the strategy for an absolute AMS measurement are presented.
Bio to come