Mixed field dosimetry using focused and unfocused laser heating of thermoluminescent materials

The incidents at the Three Mile Island and Chernobyl have triggered the need for better personnel dosimetry methods in mixed radiation fields. In mixed radiation field dosimetry, both shallow and deep doses are important. Thermoluminescent (TL) materials have been used as personnel dosimeters in mixed radiation fields. The conventional methods to extract shallow and deep doses in such mixed fields have been to use multi-element TL dosimeters with contact heating schemes (i.e., conduction or convection). This thesis presents a detailed computational study of a new method for mixed radiation field dosimetry using single-element TL dosimeters with pulsed laser heating schemes. The main objective of this study was to obtain an optimum heating scheme so that the depth-dose distribution in a thick TL dosimeter could be accurately determined. The major parts of the study include: (a) heat conduction calculations for TL dosimeters with various heating schemes, (b) glow curve calculations for TL dosimeters based on a first-order kinetic model, (c) unfolding of the depth-dose distribution based on the glow curve data, and (d) estimation of shallow and deep doses from the unfolded depth-dose distribution. Two optimum heating schemes were obtained in this study. The first one was obtained for a focused laser beam, and the second one was obtained for a uniform laser beam. Both heating schemes consist of two processes: top surface heating and bottom surface heating, and each process in turn consists of a sequence of laser pulses with various heating durations and power levels. Compared to the "true" depth-dose distribution obtained using Monte Carlo transport code EGS4, relative errors associated with the shallow and deep doses obtained from the unfolded depth-dose distributions are 5% and 25%, respectively, for the focused laser beam, and 15% in both doses for the uniform laser beam.