Graduation date: 2004

Thesis (MTech (Radiography))--Peninsula Technikon, 2003. / Word processed copy. Summary in English. Includes bibliographical references (leaves 134-141). Also available online.

Thesis--University of Florida. / Description based on print version record. Typescript. Vita. Includes bibliographical references (leaves 79-80).

The subject of this thesis is the development of new gamma ray imagers for nuclear medicine, in particular for scintimammography. The need for new compact detectors with high spatial resolution led to the design of the wavelength-shifting fibre (WSF) gamma camera, where the position of interaction of gamma rays inside an inorganic scintillator is read out by WSFs. The feasibility of the concept of a WSF gamma camera was assessed by simple analytical calculations and Monte Carlo simulations, based on the known characteristics of the individual components: the wavelength-shifting fibres, the scintillation crystal and the photodetectors. Studies were carried out of the light trapped inside WSFs coupled to CsI(Na) scintillation crystals irradiated by 122 keV gamma rays. The results confirm the feasibility of a WSF gamma camera despite the low light levels trapped in the fibres. Experimental tests of several position sensitive photomultiplier tubes (PSPMT) of the Hamamatsu R5900 series were performed to assess their suitability for the readout of scintillation crystals and of optical fibres in photon counting mode. The latter application is important for the readout of the WSFs signals in a WSF gamma camera. A WSF gamma camera prototype was built and tested. The R5900-M16 PSPMT was used to read out the signals from WSFs. The results confirm earlier predictions about its performance. In particular, the spatial resolution achieved is comparable to that of modern Anger cameras. It is expected that the inherently flexible design of the camera should allow better positioning around the object than conventional Anger cameras, which is important to optimise the spatial resolution of the system. Monte Carlo simulations show that the use of photodetectors with higher quantum efficiency than PSPMTs would significantly improve the intrinsic spatial resolution. A discussion on the most promising candidates for this application is presented.

Thesis (Ph. D.)--University of Missouri-Columbia, 1996. / Typescript. Vita. Includes bibliographical references (leaves 64-81). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 1996. / Degree granted in 1996 ; filmed in 1999. Typescript. Vita. Includes bibliographical references (leaves 64-81). Also available on the Internet.

Thesis (Ph.D.)--University of Missouri-Columbia, 2004. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

Thesis (Ph.D.)--University of Missouri-Columbia, 2004. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

It was shown that the conventional radiation dosimetric system which is based on RBE and LET is incapable of determining the likely consequences of ionising radiation exposure. Analyses of data on the induction of the chromosome aberrations, mutations and transformation in mammalian cells by radiations of different types and energies has indicated that (a) the induction of double strand breaks (dsb) in the DNA is their common critical lesion, (b) Fast ions and neutrons radiations are by order of magnitude more damaging than photons and electrons of equal mean free path, (c) Damage is through intra track action of the charged particles. A new system of radiation dosimetry, which does not require a radiation quality parameter, was proposed. It was based on the observation that for each of the biological endpoints considered an Absolute Biological Effectiveness (ABE) for damage by the charged particles can be defined as the product of the charged particle fluence and the saturation effect cross section, scaled with the efficiency (e) of damage by radiation of mean free path (lambda). e is given by 1-exp-(lambda0/lambda), where lambda0), about 1.8nm, is the mean inter-strand distance of the DNA. The physical requirements for its instrumentation, basically the emulation and quantification of the induction of dsb in the DNA, were defined. The feasibility for its realisation using detectors based on gas ionisation, superconductivity, secondary electron emission, and semiconductivity was assessed. Ultrathin films of rectified, organic semiconductors appeared to have the best potential, but such materials are not yet available in the physically characterised form as may be required for detector construction; investigations were made with available films of plastic scintillators. Experimental investigations have shown that by using coincidence techniques, plastic scintillator films can be used as a single volume 'microdosimeter', that is as counters of single strand breaks. Its use as a single volume 'nanodosimeter' is handicapped by light losses in the detector assembly which reduces the detector's sensitivity, efficiency and resolution. Semi-empirical analysis showed that the production of light from a phosphor differs fundamentally from the induction of biological damage. It was inferred that the plastic scintillators are unsuitable for instrumentation of the proposed system of dosimetry. Suggestions for future investigations were made.

Made available in DSpace on 2014-10-09T12:27:44Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:05:03Z (GMT). No. of bitstreams: 0 / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP