Gas ionization chambers with silicon nitride windows for the detection and identification of low energy ions

Thin silicon nitride membranes with a thickness of 50 nm have been tested as entrance windows to a gas ionization detector. Due to the much lower total energy loss and energy loss straggling the detector performance is dramatically enhanced compared to detectors with plastic entrance windows. For slow heavy ions the gain in resolution is most significant. For energies between 1 and 3 MeV and ions heavier than sulfur the energy resolution is up to a factor of 2.5 better than the one obtained with a heavy ion type Si-detector. It is even possible to detect 1 MeV Pu ions with a resolution of approximate to30% (FWHM). This sort of ion cannot be detected at all in a gas ionization detector with a conventional plastic entrance window as it is already stopped by 300 nm of mylar. Since a considerable improvement in resolution and particle identification is obtained, this type of ionization chambers can be used for low energy ERDA instruments and as detectors for AMS. A comparison with solid state detectors is given. (C) 2004 Elsevier B.V. All rights reserved.