Development of a High Pressure Xe Ionization Chamber for Environmental Radiation Spectroscopy

A High Pressure Xenon ionization chamber is a promising radiation detector for environmental radiation measurement due to its radiation hardness, its physical rigidity, and its capability of operation at a high temperature up to about 170 degrees C. A cylindrical high pressure xenon ionization chamber, which was configured with a shielding mesh to improve its energy resolution, was designed on the basis of an electron transfer simulation code (EGSnrc) to extract an optimal density of Xe gas and a thickness of the chamber wall. An electron drift simulation code, Garfield, which was coupled with a Maxwell electric filed calculator, was also employed for the electron drift simulations due to the geometry of the shielding mesh. Shielding inefficiency was also calculated. A spherical ionization chamber was also designed and fabricated to monitor environmental radiation. A noble gas system was constructed to create a noble gas with a high purity and to inject the noble gas Lip to 60 atm. The combination of an oxygen absorbent (Oxisorb), a molecular sieve, and a high temperature getter can minimize the electro-negative impurities, such as the O-2 and N-2 gas, to below about several ppb levels. Preliminary tests such as leakage currents, saturation currents, and gas leak test were performed. The performance of the two fabricated ionization chambers at a low dose rate was tested by using a conventional shadow technique with a NIST certified 33.52 MBq Ra-226 source in the calibration room at KAERI.