Influence of fdelta(D) on modified track structure theory efficiency calculations.

Modified track structure theory (MTST) has been successfully applied to evaluate proton-to-gamma and helium-to-gamma relative TL efficiencies in LiF by using Monte Carlo radial dose distributions and the measured dose response function, fdelta(D), of 8.1 keV X rays. In this work, an investigation is performed to study the effect of the choice of fdelta(D) for the reference test radiation field, on the predicted MTST proton-to-gamma and helium-to-gamma efficiency values. Results from two sets of calculations are presented. Set 1 investigates five fdelta(D) functions with different shapes and its influence on the MTST efficiency values while set 2 applies MTST using several fdelta(D) functions selected with fdelta(D)max ranging from 2 to 4. Comparison of the predicted efficiency values with experimental data show that the choice of 8.1 keV X rays gives the best description of the data. Results from set 2 show that predicted efficiencies may vary by as much as 44% for peak 5 and as much as 70% for the total signal among different fdelta(D). This confirms the importance of using the adequate fdelta(D) from a test radiation which simulates as much as possible the energy spectra and irradiated volume produced by the secondary electrons arising from the heavy charged particle radiation under study.