The identification and rejection of energy-degraded events in gas ionization counters

A common feature of the measurement of charged particles with gas detectors is the presence of a small fraction of events (≅ 0.1-0.2%) for which significantly less than the total ionization is recorded. These events cause an energy tailing that can seriously impair the identification functions of gas detectors used either to instrument the focal plane of magnetic spectrometers or for accelerator mass spectrometry. The anomalous, energy-degraded events are shown to arise both from reactions between the incident ions and the detector gas and, more importantly, from the scattering of ions by the gas. It is demonstrated that an appropriate detector configuration provides the means to reject most of the anomalous events, allowing the measurement of very low cross section reactions without significant background interference from such events. (orig.)