Secondary Electron Fluence Generated in LiF:Mg,Ti by Low-Energy Photons and its contribution to the Absorbed Dose

摘要

Low-energy secondary electrons (SE) produced by photons when interact with matter has been considered fundamental for better understanding radiation damage and/or dosimeter response in terms of ionization density. However, little attention has been given to this issue in the past. In this work, the contribution to the absorbed dose of SE spectra produced in LiF;Mg,Ti by ten x-ray beams (20 kV-300 kV), ~(137)Cs and ~(60)Co gamma rays has been investigated using the EGSnrc Monte Carlo Code. In particular, an independent analysis was performed to estimate the irradiated mass of LiF:Mg,Ti by taking into account the continuous slowing down approximation (CSDA) range of the electrons generated by each photon beam. This was used to re-evaluate the thermoluminescent relative efficiency, RE, of LiF:Mg,Ti exposed previously to the same beams and reported elsewhere. The results indicated that, depending on the photon energy beam, the SE spectra produced in LiF:Mg,Ti represent 40% -90% of the total spectra between 1 keV and 10 keV and consequently have a contribution of 4.3%-21% to the total absorbed dose delivered, being higher when the photon energy increases. Furthermore, the RE calculated with the new absorbed dose values shows a better agreement with that previously obtained through analytical method (maximum difference of 8% this work vs 18% previously). The results suggest that the absorbed dose imparted to the matter by low photon energy beams is not properly known and consequently the absorbed dose delivered to cells in biological research or to patients in clinical procedures can be misleading. Thus, basic investigations for better understanding the electron interaction processes with matter at low energy levels are greatly needed.