PubMed · 285979
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E C Michaud. 1979. Fluorosis.. https://doi.org/10.14219/jada.archive.1979.0165
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The energy response of three types of LiF:Mg, Ti dosemeter to standard x-ray calibration qualities and diagnostic x-rays has been studied. The aim of this study was to investigate whether the inherent mismatch between these qualities compromises the accuracy of the evaluated occupational doses in diagnostic x-ray facilities. A sample of 10 dosemeters of each type was exposed to air kerma of 5 mGy from each of six ISO 4037 (series 407) x-ray radiation protection calibration qualities (2.7 mm Al to 2.45 mm Cu HVL (half-value layer)) and 11 diagnostic x-ray qualities (1.45-4.9 mm Al HVL). The results show that the TLD energy response to ISO 4037 and diagnostic x-rays as normalised to 137Cs ranged from 1.1 to 1.44 and 0.57 to 1.54 respectively. This implies an energy response range from -52 to +7% for diagnostic x-rays relative to ISO 4037 x-rays, hence a maximum over-response of 52%. Despite this discrepancy, the results show that the mismatch between calibration and diagnostic x-ray beams does not significantly compromise the accuracy of individual doses in diagnostic x-ray facilities.
Using ancilliary optical absorption and sensitisation measurements, it is demonstrated quantitatively in the framework of the unified interaction model (UNIM) that the experimentally measured peak 5 supralinearity can be theoretically predicted for all possible dose response characteristics of the competitor.
Photon energy response of MTS-N (LiF:Mg,Ti) detectors (TLD Poland) and of MTS-N detectors sensitised with 200 Gy of 60Co gamma rays, followed by UV irradiation (sMTS-N), has been determined using X rays with narrow energy spectra, in the energy range from 20 to 300 keV. The over-response of LiF:Mg,Ti detectors for X rays (relative TL efficiency eta = 1.1) can be explained as an ionisation density effect. Low energy X rays produce short electron tracks, which locally deposit a high radiation dose and, consequently, lead to an enhanced (supralinear) response. This over-response has not been observed in sensitised MTS-N where supralinearity in the response after gamma ray doses above 1 Gy is not seen. Using the dose-response curves measured for MTS-N detectors after 137Cs gamma ray irradiation and local doses calculated using Monte Carlo generated electron tracks, it was possible to predict the relative TL effectiveness for different X ray energies. The calculation procedure can be applied to predict the photon energy response of LiF:Mg,Ti detectors in an arbitrary photon field.