Study of the energy deposition in LiF by heavy charged particle irradiation and its relation to the thermoluminescent efficiency of the material

Abstract

The initial energy deposition stage of the thermoluminescent (TL) process is investigated. A coupled ion-electron Monte Carlo (MC) transport code developed for LiF considering its solid-state nature is used to obtain radial dose distributions for incident proton and helium ions at several energies. Models which relate the initial energy deposition to the final TL light emission are used to predict TL efficiencies. Track structure theory (TST) efficiency calculations using the MC radial dose distributions and target sizes of 50, 100 and 150 Å were performed for the total signal of LiF. Comparison with recent high linear energy transfer (LET) efficiency measurements suggests a value for the target size within the interval 50-100 Å. Modified TST (MTST) proton-to-gamma and helium-to-gamma relative TL efficiency calculations were performed with the MC radial dose distributions and 8.1 keV x-rays as test radiation. It is found that both theories show good agreement with the data, though both predict an energy dependence stronger than observed. A `core radius' for a given ion may be found by applying MTST. The importance of the cut-off energy for secondary electron generation in the MC code is discussed. The fraction of ion energy deposited by the secondary electrons around the heavy charged particle (HCP) path obtained from the MC simulation is in accordance with known values. This work includes solid-state effects in the calculated radial dose distributions in LiF providing dose profiles which are necessary for the calculation of efficiency values and may prove to be essential for further understanding of HCP induced thermoluminescence in LiF.