Xenon-filled ionization detectors, due to their high atomic number fill gas (Z=54), moderate densities (~0.3 g/cm3-0.5
g/cm3) and good energy resolution (2%-4% at 662 keV), fill an important niche between more familiar technologies
such as NaI(Tl) scintillators and Germanium detectors. Until recently, difficulties with obtaining sufficient Xenon
purity, reducing microphonic sensitivity, and developing low-noise electronics compatible with small ionization signals
have hampered the development of this nuclear detection field. Constellation Technology Corporation, whose
experience with xenon detectors goes back to the mid 1990's, has made significant progress in these areas and has
developed a commercial line of detectors with active volumes ranging from small (35 g Xe) to large (1400 g Xe). Here
we will discuss our development of a mobile, large area, spectroscopic array.
New approaches to the design of high-pressure Xe (HPXe) ionization chambers are described. HPXe ionization chambers represent a well-known technique for detecting gamma rays in the energy range between 50 keV and 3 MeV. Since the HPXe detector is an electron-only carrier device, its commonly accepted design includes a Frisch-grid-a metal mesh employed for the electrostatic shielding from the immobile positive ions. The grid is a key element of the device’s design which provides good energy resolution of the detector, typically 2-3% FWHM at 662 keV. However, the grid makes the design more complex and less rugged, especially for field applications. Recently, we developed several designs of HPXe ionization chambers without shielding grids. The results obtained from the testing of these devices are presented here.
We have investigated electroluminescence (EL) detectors with uniform and axial electric field configurations, filled with xenon gas pressurized up to 35 bar. Photomultipliers placed outside pressurized vessels and avalanche photodiodes placed directly inside the pressurized xenon have been used to detect scintillation and electroluminescence signals. A light-collection system based on a cylindrical array of wavelength shifting fibers has been used to collect light in the detector with axial electric field. The EL detectors with photomultiplier readout have demonstrated exceptionally low sensitivity to vibrations. An energy resolution of 10%FWHM was measured for 60 keV gamma rays. The results are discussed and measures that will be undertaken to improve performance of the detectors are considered.