Hand-Held Gamma Detector Based on High-Pressure Xenon Gas: Determination of Charge Carrier Lifetime in Xe

The primary goal of the work is the design and construction of the hand-held gamma detector based on high-pressure xenon (HPXe). The primary use of the detector with spectrometric capabilities is the detection and identification of radioactive materials in the normal stream of commerce at rail terminals, seaports, border crossings. The advantages of the detectors are high resolution, light weight, robustness, radiation and temperature stability. A major part in reaching the project’s final goal is creation of a Xe purification facility. Xenon gas compressed up to pressure ~50 bar and sometimes doped with hydrogen, methane or others gases, which is the working medium for the high-resolution HPXe detectors, needs to be very pure. The purity level can be measured directly or, alternatively, the gas usability in gamma-spectrometers can be evaluated indirectly through the charge carrier (electron) lifetime measurements. Typically, lifetime determination methods involve the measurement and analysis of individual ionization pulses from particles registered in a Xe-filled ionization chamber. In the present paper, we studied the HPXe electron lifetime by using measurements in a cylindrical ionization chamber and developed the respective analytical charge transport model. Our results showed that it is possible to determine electron lifetime in the cylindrical configuration. The parallel plate electrode configuration was studied for comparison. The measurements were conducted in a two-electrode configuration for a range of pressure values (5–50 bar) for the Xe+0.25%H2 gas mixture and pure Xe.