Gas amplification in high-pressure pure xenon proportional counters

We obtained the properties of the gas amplification in pure Xe gas up to 1.0 MPa. It is found that the first Townsend ionization coefficient becomes larger in highly-purified Xe gas. The energy resolution slightly deteriorates with increasing gas pressure, but it is possible to make the gas pressure higher with keeping the energy resolution constant when the gas gain is under approximately 500. In the future work, we will attempt to improve the energy resolution of the Xe proportional counter. The energy resolution we obtained is worse compared with the limit of the energy resolution from statistics of the gas amplification process determined through the Fano factor and the parameter of the variance of gas amplification for one electron. Therefore, it remains possible of improving the energy resolution. Furthermore, we will study the properties of the gas amplification in pure Xe gas at the higher gas pressure. The study will furnish the basic data to develop the high-energy-resolution gamma-ray spectrometer at the energy of above 100 keV.