A Perspective from Ontario Tech University Industrial Research Chairs on 20 Years of Capacity Building in Health Physics and Radiation Science.

ABSTRACT: Ontario Tech University (University of Ontario Institute of Technology) is one of Canada's newest universities, having been incorporated in 2002. In 20 y, the University has increased enrollment from a few hundred students to over 10,000. The University was designed to be "market driven" and as such offered courses that had high market demand. The Faculty of Energy Systems and Nuclear Science was one of the first faculties to be established at the University, with the intent to fill a gap between personnel that were retiring out of the nuclear industry and the dearth of nuclear engineers and health physicists being educated in Canada. As such, the University established unique programs in both nuclear engineering and health physics/radiation science with strong input from industry stakeholders. This paper will discuss the evolution of the Health Physics and Radiation Science program at Ontario Tech from the teaching and capacity building perspective, and it provides insight regarding health physics and radiation science research at Ontario Tech under the industrial research chair program.

Investigation of the stray neutron fields produced from proton irradiated Ta, Co-59, Ni, Fe, Inconel X750 and stainless steel 310 targets in a materials testing laboratory environment.

A nested neutron spectrometer was used to measure the stray neutron fluence and ambient dose equivalent produced by protons from a 4 MV tandem accelerator on various target materials at the Reactor Materials Testing Laboratory (RMTL), Queen's University, Kingston, Ontario. The nested neutron spectrometer utilizes a Helium-3 proportional counter and measures the thermal neutron count rate as a function of moderator shell-thickness. Using custom unfolding software, neutron spectra and neutron dosimetric quantities were derived at various locations within the RMTL. The nested neutron spectrometer can be operated in both a pulse mode and current mode allowing for measurements over a wide range of accelerator beam currents. All measurements conducted at the facility were within the main accelerator chamber and experimental target rooms. Target room measurements were conducted with a variety of target materials representative of those to be used for research planned at the RMTL.

An investigation of early radiation damage in rainbow trout eye-lenses.

As part of the wider interest in the effects of ionizing radiation on non-human biota, this investigation was carried out to study early radiation damage to the eye-lenses of rainbow trout. Lenses were cultured and irradiated to doses of 1.1 Gy and 2.2 Gy with low-energy X-rays of 40 kV. Laser focal analysis was used to track changes in focal lengths across the lenses post-irradiation. Changes in focal length variability (FLV) were measured to determine whether this could give an indication of the early effects of radiation on lens health. No statistically significant differences in FLV between the control and irradiated lenses within 10 days post-irradiation were observed. FLV was found to be 0.09 ± 0.02 mm for 2.2 Gy lenses, 0.06 ± 0.01 mm for 1.1 Gy lenses, and 0.11 ± 0.02 mm for control lenses at the end of the observation period.

Sensitivity and uncertainty in the measurement of H*(10) in neutron fields using an REM500 and a multi-element TEPC.

The REM500 is a commercial instrument based on a tissue-equivalent proportional counter (TEPC) that has been successfully deployed as a hand-held neutron monitor, although its sensitivity is regarded by some workers as low for nuclear power plant radiation protection work. Improvements in sensitivity can be obtained using a multi-element proportional counter design in which a large number of small detecting cavities replace the single large volume cavity of conventional TEPCs. In this work, the authors quantify the improvement in uncertainty that can be obtained by comparing the ambient dose equivalent measured with a REM500, which utilises a 5.72 cm (2(1/4) inch) diameter Rossi counter, with that of a multi-element TEPC designed to have the sensitivity of a 12.7 cm (5 inch) spherical TEPC. The results obtained also provide some insight into the influence of other design features of TEPCs, such as geometry and gas filling, on the measurement of ambient dose equivalent.

A model for the induction of DNA damages by fast neutrons and their evolution into cell clonogenic inactivation.

It has been long stated that cellular inactivation through neutron irradiation is mainly caused by energy deposition in DNA molecules from recoiled secondary charged particles. Complexities associated with neutrons, such as the generally broad energy spectrum and the inherently wide energy spectrum of the induced charged particles, not to mention that the dependence of cellular inactivation by charged particles on radiation quality is yet to be fully understood, make it difficult to check this statement. Recently a molecular model has been proposed that improves the quantitative explanation of the dependence of cellular inactivation by charged particles on radiation quality. An attempt was made to apply this model for analysis of neutron cellular inactivation. As a preliminary result it is suggested that neutron cellular inactivation is caused not only by secondary charged particles but also by an "atomic deletion" effect, generated by a stripped atom recoiling from a DNA molecule. This effect seems to be of significant importance, the inactivation cross section of this effect for fission neutrons is as much as 15% (aerobic conditions) or 55% (hypoxic) of the total, and the severity of one occurrence of atomic deletion by a single neutron is estimated as much as 3.1 +/- 1.1 times (aerobic) or 6.8 +/- 1.2 times (hypoxic) higher than the severity of one event by a single track of a charged particle interacting with DNA.

Characterization of miniature tissue-equivalent proportional counters for neutron radiotherapy applications.

A miniature tissue-equivalent proportional counter (TEPC) system has been developed to facilitate microdosimetric measurements in high-flux mixed fields. Counters with collecting volumes of 12.3 and 2.65 mm3 have been constructed using various tissue-equivalent wall materials, including those loaded with 10B for evaluation of the effects of the boron neutron capture reaction. These counters provide a measure of both the absorbed dose and associated radiation quality, allowing an assessment of the utility and relative effectiveness of various neutron radiotherapy techniques such as boron neutron capture therapy (BNCT), boron neutron capture enhanced fast neutron therapy (BNCEFNT) and intensity modulated neutron radiotherapy (IMNRT). An evaluation of the physical parameters affecting the measured microdosimetric spectrum, the gas multiplication characteristics and the measurement of absorbed dose is presented. In addition, important aspects of the calibration and low energy extrapolation techniques for the microdosimetric spectrum are provided.