Development of Compton Imaging Device for Gamma Rays in MeV Region by The Use of High-pressure Xenon Gas

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The scope of this research is divided into three categories, radiation physics on high pressure of xenon, simulation of detectors, and basic studies on the detectors. It is found that ionization yields slightly decrease as increasing the pressure xenon from 1.0MPa to 3.0MPa. On the other hand, scintillation yields rapidly decrease according to the electric field strength less than 0.05 Td and at above that field, show constant yields which are about 40% of ones at zero electric field. However, the yields slightly increase as increasing the pressure of xenon from 1.0MPa to 3.0MPa. The scintillation yields due to recombination in xenon doped with CH^4 disappear as increasing the concentration of CH^4 from 0 to 2.0% and the drift velocity of electron swarms is rapidly increase as increasing the electric field strength. The electron temperature in high pressure xenon dramatically decreases by doping a small amount of molecular impurities such as H_2 and CH_4. It is found the effect make not only the electron drift velocity larger, but the spread of an electron swarm on drift smaller. A high pressure xenon time-projection-chamber(HPXe-TPC) is simulated as an imaging apparatus by using Compton effects in xenon. The results show an angular resolution of about 10 degree at an orbit of 100km altitude. The resolution is mainly blurred by multiple scattering of Compton recoil electrons in the case of a diffused gamma ray source and due to Doppler broadening of scattered gamma rays in the case of a point-like gamma ray source. Momenta of charged particles with an energy in MeV region are made sure to be measurable with the TPC, because a distribution of alpha-particle emission angle is possibly determined by reconstructing alpha-particle tracks measured with a two dimensional TPC under an normal pressure of xenon.