The radiological hazards from tritium are usually associated with exposure to tritium oxide either by inhalation, ingestion or permeation through skin. However, exposure from skin-contact with tritium gas contaminated surfaces represents a different radiological hazard in tritium removal facilities and future fusion power plants. Previous experiments on humans by Eakins et al. (8), and more recent experiments on hairless rats at Chalk River Laboratories have shown that when a tritium gas-contaminated surface is brought into contact with intact skin, high concentrations of organically-bound tritium in urine and skin are observed which were not seen from single tritiated water (liquid or vapour form) contamination. The results of the rat experiments, which involved measurements of tritium activity in urine and skin, after contact with contaminated stainless steel, are described. These results are also compared to previous data from human experiments. The effect of various exposure conditions and different contaminated surfaces such as brass, aluminum and glass are analysed and related to the results from contaminated stainless steel exposure. Dosimetric models are being developed in order to improve the basis for dose assessment for this mode of tritium uptake. The presently studied model is explained along with the assumptions and methods involved in its derivation. The features of 'STELLA', the software program used to implement the model, are discussed. The methods used to estimate skin and whole body dose from a model are demonstrated. Finally, some experiments for improving the accuracy of the model are proposed. Briefly, this study compares the results from animal and human experiments as well as different exposure conditions, and determine the range of whole body and skin dose that may be involved from skin-contact intake. This information is essential for regulatory purposes particularly in the derivation of doses for skin-contact contamination. / Thesis / Master of Science (MS)

Increasingly, culturally and ethnically diverse environments provide an abundance of ordinary, everyday intergroup encounters, especially in public settings---often consisting of a conglomeration of positive and negative experiences. Yet few intergroup contact studies have focused on measuring and assessing contact in public settings. Reasons for this include both theoretical and methodological considerations. However, before the impact of mundane, everyday encounters on prejudice reduction can be assessed, it is necessary to examine the following questions: (1) Which situations are perceived as intergroup contact by participants? (2) How do individuals conceptualise where the boundaries for contact lie? (3) How are public and private forms of contact typically experienced? (4) Do they differ in the ways researchers have assumed in the past? and (5) Which methods are most appropriate for assessing public encounters? How can memory bias, temporality and locatedness be taken into account? Using qualitative, quantitative and near-time in-the-field methods, the following research examines these aspects in both public and private settings and provides first insights into how a novel method---the Contact Logger---can be used to assess the effects of public and private contact on attitudes. A three-day diary/interview study (N=17) explored how contact is experienced, understood and conceptualised in a variety of everyday intergroup contexts. This was followed by a survey study (N=525) that examined the boundaries of what is typically perceived as being contact. Insights from both studies fed into the development of a context-aware mobile application, which enabled the capturing of near-time intergroup encounters in situ. The usability of the resulting research tool---the Contact Logger---was tested, leading to further refinements. Following an initial feasibility study (N=104) that explored contact between young and older people, a field experiment (N=112) examined intergenerational contact in public and private contexts. Data collected with the Contact Logger were analysed on aggregate and day-to-day levels, and where possible compared to traditional retrospective survey data. Results from the first two studies indicated that while traditional intergroup encounters, such as contact with family and friends, are clearly conceptualised and viewed as contact, experiences and perceptions of contact in public settings are more disparate. Moreover, effects of such contact on attitudes are dependent on the idiosyncratic meaning attributed to the specific encounter as well as past experiences. Near-time data from a field-experiment (Study 5) provided evidence that intergroup encounters reported in situ compared to retrospective survey data differed in key variables (i.e., contact quality, duration, perceived status and group typicality). Correlational analyses between near-time and retrospective measures showed less correspondence than expected. Further, additional day-to-day analyses revealed that attitudes towards older people were less positive during weekends than weekdays, indicating that attitudes may be more dynamic than previously thought. Findings, as well as the different methodological and theoretical approaches, are critically discussed. Finally, a broad range of further applications for the Contact Logger are presented and important limitations are discussed.