Additivity studies of X-ray and negative pion irradiations on the TL response of TLD-700

TLD-700 has been shown to be useful in negative pion dosimetry. By utilizing the 200 and 2600C peaks of the glow curve, both total and high LET radiation dose are potentially measurable. In an effort to better understand the TL response in TLD-700 to negative pions, the present study investigated the additive effect of low LET radiation (X-rays) and high LET radiation (negative pions) in TLD-700. Because of the lower dose rate of the pion beam (650 rad/hr) compared to the X-ray beam (7580 rad/hr), and because the predominant interest was in clinical single fraction dose levels (approximately 100rad/treatment) pion exposures were limited to 1000 rad and X-ray exposures to 5000 rad. Twelve combinations of X-irradiations followed by pion irradiations and their corresponding combinations of pion irradiations followed by X-irradiations were studied. Individual pion or X-ray irradiations were also measured. Results for the 200 and 2600C peaks are given. It is concluded that, for the dose levels used in this study, both the 200 and 2600C peaks show no appreciable difference in the order of exposure to X-rays and pions. For the 2000C peak the doses are additive within the statistical accuracy of the data. This conclusion tends to support the theory that the high LET radiation and low LET radiation act independently in producing thermoluminescence. (author)