Davenport, Ian John; (1994) X-ray microcalorimetry for space. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The X-ray microcalorimeter is an X-ray detector of potentially high energy resolution and quantum efficiency. The energy of incident X-rays is determined by measuring the resultant change in the resistance of a cooled semiconductor as an X-ray is incident on it. The history of X-ray microcalorimetry is reviewed, the current state of the art is placed in the context of contemporary X-ray detectors, and new X-ray detectors in the development stages. The performance of X-ray microcalorimeters is compared to other detectors. The principles of operation of microcalorimeters are discussed, and the relations between operating parameters established. The system devised and operated by the University of London microcalorimetry collaboration is described, and the future development of X-ray microcalorimetry considered. The design and implementation of a suite of computer programmes to analyse the data generated by the detector is described, and a space-based processing system defined. Results obtained with the detector operating at 100 mK in 1991 facing a Fe source are presented and analysed. A resolution of 316 eV is shown at 200mK, and 276 eV at 100mK. The absence of the expected improvement in resolution at the lower temperature is investigated. The microcalorimeter as an observational tool will require a space platform at a low temperature. Various low-temperature techniques are described, and the design and operation of the adiabatic demagnetisation refrigerator (ADR) used is described and modelled. The ADR is appraised as a means of cooling a space-based detector to 100mK, and a hypothetical system involving a 2-stage ADR is devised and modelled. One ADR operates between 100 mK and 1.0 K, and a second operates between 1.0 K and 4.0 K. The complete cooling system maintains a 100mK stage for 59 hours, with a recycle time of 17 hours. Replacing the high temperature ADR with a pumped helium tank cooling to 2.0 K increases the hold time to 80 hours, recycling in 3 minutes.

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