Microdosimetric Measurements from 0.5 um to 3 um Site-Size

The tissue equivalent proportional counter can be used as a radiation monitor in different radiation environments, included aboard a spacecraft or in aircraft for flights at high altitude. Usually the gas density is set to simulate site size of 1 um or 2 um. However, especially for sealed detectors which should work for long time without refilling, the gas density could change significantly. The immediate consequence of density variations is a gain shift, which is often reported. This however not a serious problem, because the gain can be measured and corrected by changing the applied voltage. On the other side, a more critical consequence of an increase of the density, is that the microdosimetric spectra could change significantly, deteriorating the response of the detector. This limit the reliability of sealed TEPC, especially because the gas pressure is not directly monitored. It was therefore the aim of this work: to study the response function of a TEPC filled at different gas densities, to study some features of the microdosimetric spectra which change with the gas density and to find a relation between this features and the gas density which allow to estimate the gas density when it is not directly measurable.