PROBLEMS ASSOCIATED WITH LARGE SCALE PERSONNEL MONITORING OF PHOTONS USING LITHIUM-FLUORIDE TLD-100 (THERMOLUMINESCENCE, PRECISION, ACCURACY, RADIATION

The dosimetric properties of a large batch of lithium fluoride TLD-100 dosimeters when exposed to photons for total absorbed doses in the region from 0.1 - 1.0 mGy (10 - 100 mr) have been examined in this work. This region is of particular importance because in many operational health physics situations the majority (>90%) of all recorded absorbed doses to personnel lie in this region. With the possibility that occupational radiation dose limits may be reduced in the future, accurate monitoring of individuals in this region will be of prime importance.;The use of lithium fluoride thermoluminescent dosimeters rather than photographic emulsions to monitor radiation exposures is becoming more and more widespread. The majority of systems use lithium fluoride TLD-100, a dosimetry phosphor manufactured by the Harshaw Chemical Company. Favorable characteristics of this material include its near tissue equivalence and reusability. The popularity of this material can be guaged from the USAF's decision to switch entirely from film to a TLD-100 based dosimetry system, making them the largest single user of this material.;It is important to realize, however, that accurate dosimetric measurements in the region from 0.1 to 1.0 mGy are difficult to accomplish on a large scale if the inherent characteristics of the material are not fully understood. The purpose of this thesis was to point out several effects which could compromise accurate dosimetric measurements in this region and to suggest some methods to minimize them. These effects include the effect of TLD batch composition, overresponse of the dosimeter to low energy photons, dose rate effects, the effects of storing the dosimeter before readout, and possible interference from ultraviolet and radiofrequency radiation. Each of these items can cause errors which can range up to 70%, depending on the total absorbed dose and the particulars of the radiation exposure. One effect which is of extreme interest is the induction of a thermoluminescent signal by radiofrequency radiation. Although this effect can cause gross errors in estimating the ionizing dose, it opens the possibility that LiF or another phosphor may have an application as a non-ionizing radiation dosimeter.