Advances in particle identification in AMS at low energies

Special gas ionisation detectors have been developed for AMS at low energies (0.3–3 MeV). By using very thin silicon nitride foils as entrance windows and low-noise preamplifiers, significant improvements in the performance has been obtained. In addition, electronic noise has been reduced by a compact design which minimises cable length and input capacitance. The resolution has been systematically studied as a function of energy for various projectiles ranging from protons to uranium. Energy straggling in the thin entrance foil is only a minor contribution to the total energy resolution. For heavier ions zp > 6 the resolution is limited by the statistical nature of the ionisation process in the counter gas. For light elements, the electronic noise is the dominant contribution to the resolution. Particle identification with ΔE − E techniques has been studied as well. Good isobar separation for 10Be–10B can be obtained in the energy range of 0.3–0.8 MeV. Also isobaric molecules such as BeH and CH can be identified in the energy range of 1 MeV. These advances in detector performance represent an essential step forward in the development of multi-isotope AMS facilities at low energies. The detector development has also a potential for application in other fields of research where good energy resolution and particle identification is needed.