New and upgraded ionization chambers for AMS at the Australian National University

Three state-of-the-art ionization chambers have recently been designed at the Australian National University (ANU) to further enhance the isotopic and isobaric separation capabilities of the AMS setup at the Heavy Ion Accelerator Facility (HIAF). Two compact split-anode ionization chambers with low noise preamplifiers allow for measurements of actinides and other radioisotopes that do not have atomic isobar interferences. Both assemblies sit inside Dependex-100-Tees and are constructed such that they are retractable from the ion beam under vacuum. A high energy resolution version will be used for Pu, I-129 and Fe-55. The second detector serves as the final energy detector in a time-of-flight setup and is employed for U-236 and Pb-210 detection. The new Flexible-AntiScattering Multi-Anode (FASMA) detector is a 7-anode ionization chamber optimized for the discrimination of Mn-53 from Cr-53 in the gas-filled magnet setup with the ENGE-split-pole spectrograph. The entire setup was simulated with Raytrace and SRIM. Finally, an existing 8-anode ionization chamber has been upgraded and now provides a Zr-93-Nb-93 isobar suppression of 5 x 10(4) resulting in the best limit of detection for Zr-93 of any AMS-facility. This article details the various features of these detectors and compares first experimental results to performance values expected from modelling.