An Imaging Detector for Hard X-Ray Astronomy.
Abstract
Available from UMI in association with The British Library. The next generation of hard X-ray (20-250 keV) telescopes will require high sensitivity, good timing and spectral resolution. They will also require a high angular resolution imaging capability. To this end, a laboratory prototype detector has been designed and built. It is a development of the classic rotation modulation collimator (RMC), with two significant differences. The first innovation is the incorporation of the lower grid into the detector, in the form of alternate strips of NaI(Tl) and CsI(Tl). 'Phoswich' pulse-shape discrimination techniques are employed to differentiate between energy deposits in the two materials. As a consequence the sensitivity of the detector is doubled. The second improvement is the use of a number of RMC modules with different angular resolutions (multi-pitch RMC), in order to synthesise images with reduced sidelobes. The imaging properties of the multi-pitch RMC have been examined in detail, both for ideal situations and also non-ideal. The constructional defects with the most serious consequences are modulator and detector stripes of different widths, or non-parallel grids. However, the greatest sensitivity loss is expected to be due to the addition of the images from identical modules with different mathematical weights, but even this loss is only about 10%. A proposed hard X-ray astronomy satellite with multi-pitch RMC imaging is described. The detectors will be developed from the laboratory prototype. A 600kg spacecraft could carry detectors with a total area of 3000cm ^2, with an estimated sensitivity of 3 times 10^{-6} photons cm^{-2} s ^{-1} keV^{ -1} in 10^5 seconds, and an angular resolution of less than 20 arc minutes. The energy resolution of scintillator/photomultiplier detectors is considered in the final Chapter. Photon and photoelectron statistical fluctuations are the dominant effects, but variations in light collection efficiency and photocathode non-uniformity may also be important, and detector design must take these factors into account.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- 1988
- Bibcode:
- 1988PhDT........16F
- Keywords:
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- Engineering: Electronics and Electrical, Remote Sensing, Physics: Astronomy and Astrophysics