Particle identification with appropriate detector systems is very essential for the performance of AMS facilities.At low energies this identification is more difficult. At our laboratory systematic investigations with gas ionisation detectors have been performed in recent years in order to improve their performance. Significant progress has been made by using silicon nitride entrance windows, which are much thinner and more homogenous than the foils made from organic materials such as mylar or polypropylene. Also the electronic noise was reduced by more than a factor of 3 by appropriate detector design and by the use of low noise preamplifiers.So the overall performance has been improved enormeously.
These technical improvements lead to a situation, in which the physical processes such as energy and angular straggling in entrance foil and detector gas, as well as the statistical fluctuations in the ionisation process are the dominant factors limiting the resolution. These limitations will be discussed in more details. The performance, which is presently possible, is shown by various examples. The total energy resolution is better than what can be reached with Si detectors for all elements heavier than beryllium. Isobar separation is even possible at energies of a few hundred keV for 10Be-10B. The 36Cl-peak can be separated from the corresponding peak of 36S at energies below 3 MeV.
The new detectors provide also separation of molecular interferences, which can be essential when analysing ions in charge state 1+ and 2+. The following molecular interferences were separated by the dE-E technique:10Be - 9BeH , 14C - 13CH,12CH2, 26Al - 12C14N,10B16O,13C2.
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See more of The 10th International Conference on Accelerator Mass Spectrometry (September 5-10, 2005)