Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001phdt........16s&link_type=abstract
Thesis (PhD). WASHINGTON UNIVERSITY, Source DAI-B 62/06, p. 2758, Dec 2001, 217 pages.
Astronomy and Astrophysics
Astrophysics
Scientific paper
This dissertation reports on the studies of an orthogonal cross-strip CdZnTe detector for high-energy X-ray (20-250 keV) astrophysics applications. The intrinsic three-dimensional detector response and the effectiveness of using various shielding techniques at balloon altitudes are investigated. This detector has great promise for use as the imaging detector of a large- area, coded-mask instrument in an all-sky high-energy X- ray survey or as the focal-plane detector for an X-ray focusing telescope (Constellation-X) for high throughput, high resolution X-ray spectroscopy (6-40 keV). The most recent hard X-ray all-sky survey was conducted by HEAO-1/A4 in 1978, and one has not been conducted since then due to performance limitations of available X-ray detector technology. The next generation instruments need to have sub-degree angular resolution, good sensitivity in the hard X-ray band (3σ sensitivity to sub- mCrab), and few keV energy resolution. This performance is demonstrated using a discriminator-grade Cd0.9Zn0.1Te detector, with dimensions of 1.2 cm x 1.2 cm x 2 mm and a novel 500 μm pitch electrode design. The cathode has 450 μm wide strip electrodes and the anode has 100 μm strip electrodes. Interleaved between the anodes is a 100 μm wide ``steering'' electrode, held at 10% lower bias than the anodes. The lower electric field helps ``steer'' the electrons onto a single anode electrode, as opposed to the dead space between anodes and reduces the amount of sharing among anode electrodes. Three-dimensional position information is obtained by the correlation of the charge induced on the anode, steering electrode and cathode strips. Two high altitude balloon campaigns have been conducted to investigate the performance of the first position-sensitive CdZnTe detector at balloon altitudes and the effect of various shielding schemes on reducing the background. Background levels suitable for a wide to moderate field of view have been demonstrated at (4 +/- 1) × 10- 4 cts/cm2-s-keV for 30-50 keV with prompt cosmic-ray anticoincidence rejection. The background level achieved with ~100 keV shield anticoincidence rejection is 1.4+0.9-0.6 × 10-4 cts/cm2-sec-keV for 30-50 keV, which is within a factor of 2 of the Constellation-X requirement.
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