Remodelling a multi-anode ionisation chamber detector for accelerator mass spectrometry of 53Mn

Abstract

Accelerator Mass Spectrometry (AMS) is a single-atom counting technique that measures the abundance of rare, long-lived radioisotopes using only milligrams of sample. The astrophysical radioisotopes 53Mn and 60Fe have been utilised for many applications including meteoritics, exposure dating, and the search for near-Earth supernovae. 53Mn measurements at the ANU have been limited to sensitivities above 10^-13 by insufficient suppression of the stable isobar, 53Cr. To expand the applications accessible to 53Mn analysis, a new detector was ommissioned that will improve the available sensitivity. This thesis covers the implementation of the new Flexible Anti-Scatter Multi-Anode (FASMA) detector. Simulations were conducted to determine the optimal placement of the detector inside the gas-filled magnet, and to assist with the design of aew multi-anode configuration. The FASMA detector was successfully tested and full spectra were recorded. These preliminary results indicate an improvement in the achievable sensitivity, even without the suppression of scattered particles. With further work, the FASMA detector should reach a sensitivity at or below 10^-14, which is competitive with the best reported level in the field. Long-lived radionuclides, such as 53Mn and 60Fe, are important for extracting the exposure history of meteorites, both in space and on Earth, as well helping to identify their origin. In light of this, cosmogenic 53Mn and 60Fe ratios were measured in ten meteorite samples. Since the available data on live 53Mn and 60Fe is scarce, these measurements will improve the constraints on current production rate models for meteorites. Show more