Gas Detector Developments in AMS: Vertical position, total energy, and Bragg detector

Department of Nuclear Physics and Accelerator Applications, The Australian National University, Canberra 2601

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Published online: 13 May 2026

Abstract

Gas ionisation chamber detectors are the workhorses of Accelerator Mass Spectrometry (AMS), providing essential isobar suppression and ion identification. Continued developments in detector resolution, performance, and reliability directly translate into improved AMS sensitivity and precision. In this contribution we report three recent developments in the gas detectors used at the Australian National University (ANU). First, we demonstrate a cathode-based vertical position measurement in the Flexible Anti-Scatter Multi-Anode (FASMA) detector, achieving a vertical position resolution of 1.71 mm (FWHM) and using this information to diagnose and correct incomplete charge collection onto the first anode. Second, we implement an independent total-energy measurement based on the grid signal in the single-grid, multi-anode FASMA detector, obtaining an energy resolution of 2.1% (FWHM), improved relative to 2.8% from the conventional anode-sum signal. Third, we describe the design of a new Bragg detector under construction at ANU and discuss analogue and digital analysis techniques for ion identification. Commissioning of the Bragg detector is expected in early 2026. These detector developments are expected to lead to enhanced isobar discrimination and measurement accuracy in future AMS campaigns at ANU.