A coded aperture telescope for low energy gamma-ray astronomy
A coded aperture telescope for low energy gamma-ray astronomy
A low energy gamma-ray imaging telescope based on coded aperture techniques has been developed for astronomy in the energy range 200 keV to 10 MeV. The telescope (ZEBRA) has a fully coded field of view of 7.0ox7.7o and a partially coded field of view of 12.8ox14.3o for an aperture to detector separation of 4.0m. The position and energy resolution performance of the complete NaI(Tl) gamma-ray detection plane has been measured and the results compared with theoretical predictions. Analysis of the data from the detector led to a description for the errors in the calculation of the event energy loss and position in the detector and to the inclusion of look up tables and a calibration system for the flight detector. The typical position and energy resolution of a single position sensitive detector element was measured as approximately 2.1 cm and 15% FWHM respectively at 661.6 keV. One dimensional imaging tests have been used to develop an understanding of the sources of error in coded aperture imaging. As a result, a theoretical description of the instrument point spread function was derived. Following the single detector tests, an array of flight detectors was assembled and two dimensional images were taken in the laboratory using a scaled down coded aperture mask. Various methods of decoding the data have been considered including the use of the Maximum Entropy Method (MEM). The angular resolution of the telescope has been obtained by measuring the minimum resolvable separation of two point sources. The results indicate an angular resolution of 79 and 23 arcminutes for linear and MEM restorations respectively. The effect of partial coding and partial data loss has been investigated and suitable methods for restoring the data developed, including the possibility of imaging within the partially coded field of view. The effect of systematic background variation on the restoration of ZEBRA images has been simulated and a suitable restoration technique has been demonstrated. Finally, the sensitivity of the ZEBRA telescope has been determined for continuum and line emissions and the predicted imaging quality obtained by simulation. (D75981/87)
University of Southampton
1987
Yearworth, Michael
(1987)
A coded aperture telescope for low energy gamma-ray astronomy.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
A low energy gamma-ray imaging telescope based on coded aperture techniques has been developed for astronomy in the energy range 200 keV to 10 MeV. The telescope (ZEBRA) has a fully coded field of view of 7.0ox7.7o and a partially coded field of view of 12.8ox14.3o for an aperture to detector separation of 4.0m. The position and energy resolution performance of the complete NaI(Tl) gamma-ray detection plane has been measured and the results compared with theoretical predictions. Analysis of the data from the detector led to a description for the errors in the calculation of the event energy loss and position in the detector and to the inclusion of look up tables and a calibration system for the flight detector. The typical position and energy resolution of a single position sensitive detector element was measured as approximately 2.1 cm and 15% FWHM respectively at 661.6 keV. One dimensional imaging tests have been used to develop an understanding of the sources of error in coded aperture imaging. As a result, a theoretical description of the instrument point spread function was derived. Following the single detector tests, an array of flight detectors was assembled and two dimensional images were taken in the laboratory using a scaled down coded aperture mask. Various methods of decoding the data have been considered including the use of the Maximum Entropy Method (MEM). The angular resolution of the telescope has been obtained by measuring the minimum resolvable separation of two point sources. The results indicate an angular resolution of 79 and 23 arcminutes for linear and MEM restorations respectively. The effect of partial coding and partial data loss has been investigated and suitable methods for restoring the data developed, including the possibility of imaging within the partially coded field of view. The effect of systematic background variation on the restoration of ZEBRA images has been simulated and a suitable restoration technique has been demonstrated. Finally, the sensitivity of the ZEBRA telescope has been determined for continuum and line emissions and the predicted imaging quality obtained by simulation. (D75981/87)
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Published date: 1987
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Local EPrints ID: 461389
URI: http://eprints.soton.ac.uk/id/eprint/461389
PURE UUID: fb9e838e-3512-480a-91e9-a11256ebe158
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Date deposited: 04 Jul 2022 18:45
Last modified: 04 Jul 2022 18:45
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Author:
Michael Yearworth
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