TLD-100 thermoluminescent efficiencies for low-energy ions: correlation of efficiency with ion incident energy

Abstract

A systematic investigation of heavy charged particle-to-gamma thermoluminescent (TL) efficiencies has been performed for the total signal and peak 5 of LiF : Mg,Ti (TLD-100) dosemeters. Experimental and theoretical efficiencies are presented for protons as well as helium, carbon, nitrogen and oxygen ions. Proton, helium and carbon irradiations were performed at incident energies between 0.7 and 11 MeV. For nitrogen and oxygen, two energies, corresponding to 'mirror' values below and above the Bragg peak energy, were used to measure TL efficiencies for the same linear energy transfer (LET) entrance value. The energies chosen were 4.83 and 9.95 MeV for nitrogen ions and 6.02 and 12.95 MeV for oxygen ions. Distinct curves are found for each ion species. Data for energies higher than the Bragg peak energy follow the well-known tendency, efficiency values decrease with increasing LET. Efficiencies measured below the Bragg peak display the opposite effect, efficiency increases with increasing LET. Presenting results as a function of incident energy shows a monotonic and single valued behaviour, efficiency decreases with decreasing energy. The measured efficiencies of the higher-energy data (above the Bragg peak) were found to be 1.45 times greater than their low-energy counterparts. Modified track structure theory efficiency calculations were performed for all the ions investigated using radial dose distributions obtained via Monte Carlo simulations in solid-state LiF and 8.1 keV x-rays as test radiation. The theoretical values show agreement with data within 40% for both peak 5 and the total signal. The calculations predict the observed behaviour, higher efficiency for higher ion energy.

Ionization density effects following F-centre optical excitation in LiF : Mg, Ti (TLD-100): analysis via track structure theory

“…These conflicting results suggest the existence of surface effects leading to anomalous TL characteristics. Mercado Uribe and Brandan [33] reported f (D) max = 1.1 ± 0.1 for 20 keV electron irradiation substantially lower than the value of 1.8 ± 0.2 reported for 8.1 keV x-ray irradiation by the same group using reportedly identical experimental protocols and in contradiction to the well-documented observation of decreasing supralinearity with decreasing energy [34,35]. Surface effects leading to anomalous values of TL efficiency following low energy electron irradiations were also reported by Lasky and Moran [36] who suggested that this was due to impurities diffusing into the sample during annealing.…”