Gamma ray induced sensitization and residual thermoluminescence in common TLD phosphors

The gamma ray induced sensitization in common TLD materials such as Lif TLD-100, CaSO4:Tm, Mg2SiO4:Tb, CaF2:Dy, Li2B4O7:Mn and CaF2:Mn was studied. The sensitization factors for the first four materials, after a pre-exposure of 1.3 x 105 R and post-annealing at 2800C for 1 hour, were found to be 5, 4, 3.3 and 1.85 respectively. All the sensitized materials were found to exhibit intense residual TL (RTL) at high temperatures. After annealing at high temperatures, the sensitization and the RTL in these phosphors were found to disappear. Li2B4O7:Mn and CaF2:Mn did not exhibit either sensitization or RTL. With the exception of LiF-TLD 100, all the sensitized materials exhibit changes in their glow peak structure compared to the respective virgin phosphors. This indicates that a change in the trapping efficiency is responsible for sensitization in these materials. The dependence of sensitization on RTL in CaSO4:Tm was studied in detail as a function a post-annealing temperature. The results indicate a competition, between the traps responsible for sensitization and RTL, while capturing the charge carriers