Characteristics of charge amplification in a proportional counter filled with high-pressure xenon

The characteristics of charge amplification in high-pressure xenon were studied using a cylindrical proportional counter. The investigated pressure range was from 0.5 to 3.0 MPa, which is higher than previous studies. The charge amplification factor was obtained between 15 and 2.4 × 10³ for investigated pressure. The first Townsend ionization coefficient was determined from the measured charge amplification factors. As a result, the ratio of α/N at higher pressures seems to increase for the same reduced electric field, which was observed approximately above 2.0 MPa. Consequently, α/N cannot apparently be represented as a function of reduced electric field only. It was found that a proportional counter is worked at weaker reduced electric field at higher pressures. This fact results in the complexity of electron avalanche processes and the deterioration of the energy resolution The non-uniformity of the anode wire would also be a cause of fluctuation of charge amplification particularly at high pressures. The energy resolution was observed to become worse with increasing pressure, which is attributed to above reasons. Nevertheless, the energy resolution in pure xenon is found to be superior to that in xenon-based gas mixtures at high pressure and several hundreds of the charge amplification factor. Further considerations about the first Townsend ionization coefficient in high-pressure xenon will be made in the future, together with the charge amplification in liquid xenon It may also be interesting to compare the behavior of charge amplification in cylindrical proportional counters at high pressure with parallel plate chambers at low pressure at the same reduced electric field. That will be important for better understanding of the mechanism of charge amplification in cylindrical geometry, or non-uniform electric field conditions.