Thesis Abstracts 2004
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Use of a Liulin Detector for the Determination of Aircrew Radiation Exposure
By: Frank W. Kitching (MASc. Nuclear Engineering)
Supervisors: Dr. B.J. Lewis and Dr. L.G.I. Bennett
Abstract
As a result of ICRP-60 (1990) recommendations, countries throughout the world have recognized the fact that, as a result of their occupation, aircrew are exposed to levels of radiation higher than that received by the general population. Some countries have implemented legislation to monitor aircrew exposure while others have implemented a system of education by issuing advisories and circulars. In Canada, legislation is not yet in place to ensure that aircrew are properly monitored, but Transport Canada has initiated studies into how the problem of monitoring all aircrew personnel can be effectively and efficiently undertaken. ICRP-60 recommended the use of predictive codes to monitor exposure with the caveat that the code be periodically verified through the use of instrument measurements.
Towards this goal, the Royal Military College of Canada has been researching aircrew radiation exposure and providing insight into a solution for long-term monitoring on behalf of Transport Canada. To further this research, a LIULIN-4N LET Spectrometer was obtained for study and comparison with the Tissue Equivalent Proportional Counter (TEPC). The TEPC has been used as a reference instrument for aircrew exposure studies. Both instruments provide a measurement of absorbed dose but, unlike the TEPC, the LIULIN does not provide a measurement of the ambient dose equivalent. This fact currently limits the usefulness of the LIULIN for aircrew exposure monitoring.
In this thesis, three different methods of determining the ambient dose equivalent using the LIULIN instrument are investigated. All three methods require that the quality factor be determined in order to calculate the ambient dose equivalent given the absorbed dose. The first method is dependent upon the aircraft’s position (latitude and longitude) and the cut-off rigidity associated with this geographical position. The second method determines a quality factor based on the complete linear energy transfer (LET) spectrum of the incident radiation recorded by the LIULIN. The third method uses probability distribution analysis to determine the dose mean LET, which can also be related to a quality factor.
All three methods satisfactorily calculate the ambient dose equivalent when compared with the reference HAWK instrument. The preferred method of determining the ambient dose equivalent was found to be a direct analysis of the LIULIN LET spectrum. As a result of this study, the LIULIN was found to be capable of providing an accurate indication of ambient dose equivalent and can be used for periodic validation of predictive codes.
