This thesis describes the development and improvement of prompt gamma neutron activation analysis and x-ray fluorescence techniques with the goal of reducing the minimum detection limit of cadmium and mercury for non-invasive measurement of occupationally exposed individuals. The detection of cadmium in the liver and kidneys with prompt gamma neutron activation analysis was investigated in this thesis. The cadmium minimum detection limit was determined to be 1.7 mg in the kidney and 3.3 ppm in the liver. This represents a reduction in the minimum detection limit by a factor of 2 in the kidney and 1.4 in the liver, and this improvement was achieved through optimization of a 238Pu-Be-based prompt gamma neutron activation analysis system at McMaster University. This system is now ready for in vivo measurement of cadmium-exposed workers, and possibly for individuals with high levels of environmental exposure. The prompt gamma neutron activation analysis technique was determined to be unsuitable for in vivo mercury measurement in the kidney due to a high detection limit of 315 ppm. This figure was a factor of 23 worse than the detection limit of cadmium in the kidney, when a factor of 10 worse was expected. A comparison was made of mercury and cadmium to chlorine, which is a well-known neutron activation element, and the source of discrepancy was determined to be the enhanced detectability of cadmium due to the non-thermal nature of the 238Pu-Be neutron energy spectrum and the non-l/v behaviour of the cadmium thermal neutron capture cross-section. Since the prompt gamma neutron activation analysis technique was not sensitive enough for mercury detection, a source-based x-ray fluorescence system was developed. This system is based on a 109Cd source that emits 88 keV gamma-rays, a source collimator and planar hyperpure germanium detector in a backscatter (approximately 180°) geometry. Minimum detection limits of 3.9 ppm for a bare kidney phantom and 5.0 ppm for a kidney phantom at 1 cm depth in a torso phantom were obtained. The planar detection system reduced the bare phantom minimum detection limit by a factor of 11 compared to previous source-based x-ray fluorescence studies, however the torso phantom minimum detection limit remains comparable to that of polarized x-ray fluorescence studies. Attempts at improving the mercury minimum detection limit with a cloverleaf detection system (detector consisting of four electronically separate hyperpure germanium crystals) and stronger gamma-ray source were not successful, and currently both the planar and cloverleaf detection systems have a similar minimum detection limit of about 5 ppm at 1 cm kidney depth. In addition, the in vivo measurement of two patients with possible mercury exposure using the cloverleaf x-ray fluorescence system is discussed. / Thesis / Doctor of Philosophy (PhD)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/29781 |
| Date | 12 1900 |
| Creators | Grinyer, Joanna |
| Contributors | Chettle, David R., Medical Physics |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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