Mercuric Iodide X- and Gamma-Ray Detectors for Space Applications
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MERCURIC IODIDE X- AND GAMMA-RAY DETECIORS FOR SPACE APPLICATIONS JAN S. IWANCZYK
Xsirius, Inc., 4640 Admiralty Way, Suite 214, Marina del Rey, CA 90292 ABSTRACT Recently, substantial progress has been made in the development of HgI 2 detectors and
associated electronics for space instrumentation.
The many technical challenges in the
instrument development involving spectroscopy performance, power consumption, weight, size,
operation over wide ranges of temperature and ambient gas pressure, and others have been overcome.
Descriptions of instrumentation under development such as: x-ray and alpha
backscattering spectrometer, scanning electron microscope and particle analyzer, M6ssbauer spectrometer, and gamma-ray spectrometer are given. INTRODUCTION There is a great need for new x-ray and gamma-ray detectors for space applications. Space instruments have very stringent constraints regarding minimal power consumption, small size, large operating temperature range, radiation damage resistance, mechanical ruggedness and reliability over long periods of time. Many terrestrial laboratory detector systems exhibit excellent performance, but their use for space missions often presents formidable problems. For example, x- and gamma-ray spectrometer systems based upon silicon lithium drifted, Si[Li] and germanium, Ge, detectors offer very low electronic noise and high energy resolution when cooled to near-liquid nitrogen temperatures. This requires the incorporation of radiative coolers in the spacecraft because the alternative techniques for cooling would consume too much power and/or have too short an operating lifetime. Yet, the incorporation of radiative cooling is also extremely undesirable. For the last decade, new x- and gamma-ray spectrometers based on a room temperature operated mercuric iodide detector technology, has been advanced considerably. The goal has been to develop a detector which combines the advantages of room temperature operation with the excellent energy resolution of cryogenically cooled spectrometers. The elimination of the cryogenic coolant and its associated vacuum cryostat permits the design and construction of high performance, compact, and lightweight detection systems. Significant progress has been achieved in HgI 2 detector performance through improvements both in fabrication technology [14] and low noise amplification electronics [5-8]. Energy resolution of 200 eV (FWHM) or better at 6 keV is achievable without the need for cryogenic cooling [2 ]. The long-term stability of the detectors is an important criterion in all applications, especially space missions. We have entered into a program of long-term testing of HgI 2 detectors under adverse conditions such as: vacuum, temperature cycling, and radiation [2,9,10]. The units have shown practically no change in performance in the vacuum condition under bias for over five years of testing and as much as seven years of shelf storage. In radiation damage tests, we have employed 10.7 MeV protons at Argonne Laboratory and 1.5 GeV protons at
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