The development of an imaging low energy gamma ray telescope

Gil, Antony (1986) The development of an imaging low energy gamma ray telescope. University of Southampton, Doctoral Thesis.

Abstract

A telescope has been developed that is capable of generating images of the gamma ray sky with a precision of one arc minute over the energy range 200 keV to 10 MeV. The instrument is based on the coded aperture technique in which a coded mask is used to cast a shadow onto the focal plane of the telescope. The shadowgram is subsequently decoded to reconstruct an image of the sky. An array of one dimensional position sensitive detection elements is employed to form a large area detection plane that is well shielded from background events. The individual sodium iodide detector bars are capable of locating the position of interaction of a 662 keV photon with a precision of approximately 2.1 cm FWHM over the 55 cm length of the detector. An energy resolution of typically 11% FWHM is achieved at this energy, which is comparable with good quality, non position sensitive sodium iodide devices. The technique of coded aperture imaging allows the observation of more than one source within the field of view of the telescope, whilst maintaining a high angular resolution. The space multiplexing of source and background data over the detection plane also effectively removes the major problem of time variable background which can cause large errors in the measurement of source flux. The thesis concentrates on the evaluation of the performance of the position sensitive detectors that make up the focal planes of the telescope, and on the development of a laboratory gamma ray imaging system. The scaled down system was used to experimentally determine the quality of image that could be obtained from the telescope and ascertain any problems that might occur. (D74274/87)

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