Bibliography: p. 171-173.

Tritium is a radioactive hydrogen isotope that is typically produced via neutron interaction with heavy water (D2O), producing tritiated water (DTO). As a result of this, tritium accounts for roughly a third of all occupational exposures at a CANDU type nuclear power plant. This identifies a need to study the biological effects associated with tritium (and low energy electrons in general). However, there are complications regarding the dosimetry of tritium, as well as difficulties in handling and using tritium for the purposes of biophysics experiments. To avoid these difficulties, an experiment has been proposed using photons to mimic the beta decay energy spectrum of tritium. This would allow simulation of the radiation properties of tritium, so that a surrogate photon source can be used for biophysics experiments. Through experimental and computational means, this work has explored the use of characteristic x-rays of various materials to modify the output spectrum of an x-ray source, such that it mimics the tritium beta decay spectrum. Additionally, the resultant primary electron spectrum generated in water from an x-ray source was simulated. The results from this research have indicated that the use of characteristic x-rays is not a viable method for simulating a tritium source. Also, the primary electron spectrum generated in water shows some promise for simulating tritium exposure, however further work must be done to investigate the slowing down electron spectrum. / UOIT

A scintillation counting system has been constructed with the use of BC-400 and EJ-212 series plastic scintillators along with a subminiature photomultiplier tube to investigate the effect of increasing plastic scintillator thickness on system-integrated counts. Measurements have been carried out using four different gamma sources with different energies ranging from 6keV to 1.332MeV and a Ni-63 beta source of maximum energy of 66keV. A simulation was also carried out in MCNP4a to verify the number of H-3 beta particles with max energy 18.6keV that would reach the plastic scintillator in a vacuum setting as well as in an air medium. Scintillator thicknesses ranged from 10μm to 2500μm. The response of the system was determined by measuring the integrated counts as a function of scintillator thickness. The results of these measurements showed the expected positive linear correlation between scintillator thicknesses and integrated counts for all the gamma sources while the slopes of the correlations of each gamma source was a function of the source energy. The beta particle response showed an initial increase of counts with scintillator thickness followed by a slight decrease. The MCNP simulation confirmed an analytical calculation of the fraction of H-3 beta particles for a given air concentration that would reach the scintillator. These results in conjunction with the experimental findings were used to assess the potential of a plastic scintillator system forming the basis of a tritium monitor for the detection of tritium in high-energy gamma backgrounds for Canadian nuclear power workers. / UOIT

The MicroImager is a fast, high resolution, real time, digital autoradiographic imaging tool with broad applications. This study utilizes the MicroImager to evaluate radiolabeled drug behavior in subcutaneous tissue. Experiments were conducted in conjunction with mathematical models to determine the diffusion coefficient (D) and elimination constant (k) for radiolabeled dexamethasone. Osmotic pumps containing [3H]dexamethasone were implanted into rat subcutaneous tissue over 6h, 24 h, and 60 h. Local tissue was explanted and slides were prepared for imaging. The MicroImager was then used to quantify the local concentration of 3H-dexamethasone in the tissue surrounding the tip of the osmotic pump. Betavision+ software was used to obtain local concentration profiles. These were then compared to a mathematical model to determine the diffusion coefficient and elimination constant for the radiolabeled drug. The diffusion coefficient for dexamethasone in rat subcutaneous tissue is 4.11 ± 1.77 x 10-10 m2/s. The elimination constant is 3.65 ± 2.24 x 10-5 s-1.A similar experiment was conducted to determine the diffusion coefficient through different means. [3H]dexamethasone was injected into the rat subcutaneous tissue for a 2.5 min and a 20 min period. A different mathematical model was applied and the diffusion coefficient was found to be 4.01 ± 2.01 x 10-10 m2/s.

Thesis (Ph. D.)--University of Washington, 2007. / Vita. Includes bibliographical references (p. 210-216).

Thesis (M.S.)--University of Michigan, 1971.

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