DETECTION OF SNM WITH HIGH-PRESSURE XENON DETECTORS*

High-pressure xenon ionization chambers have been constructed that demonstrate a number of desirable features which make them potentially useful as detectors for hard x-ray and gamma spectroscopy. They exhibit high quantum efficiency at 200 keV, medium resolution (~2% at 667 keV) and can be scaled up to kilograms of active material, without requiring difficult crystal growth and materials processing. For detecting gammas above 2 MeV, the double escape peak from pair production is shown to be a useful mechanism. These detectors are capable of unequivocally identifying U-232, U-235, U-238 and Pu-239 by well-known characteristic gamma rays that are clearly resolved. They operate at room temperature with very low power consumption, and are not vulnerable to thermal shock, mechanical deformation or neutron damage. Certain physical parameters such as fluid density, electron drift mobility, and gamma absorption cross sections establish an envelope of performance in given regions of the spectral range. Practical considerations such as amplifier noise, microphonics, impurities, strength and weight of container materials and cost of construction can also limit the level of performance that is actually achievable in a fieldable device. Considering all of these factors, xenon-based detectors can be optimized for specific applications such as the detection of Special Nuclear Materials (SNM) where they may outperform other competing technologies. Both portable instruments and large fixed installations are practical.