Development of a thermoluminescent Li2B4O7:Tm dosimeter

With the aim to develop a material that shows the necessary properties for the production of a solid state radiation dosimeter thulium doped lithium tetraborate (Li2B4O7:Tm) was studied. This material shows a thermoluminescent effect (TL) and was produced in laboratory in policrystalline and glass forms. Several techniques were utilized to characterize this material: optical absorption, fluorescence, electron paramagnetic resonance and thermoluminescence. With these techniques the effect of the radiation on the Li2B4O7:Tm was studied through the electronic transitions (absorption and emission) of the Tm3+ as well the valence reduction Tm3+ Tm2+. This effect was indirectly corroborated through EPR data that showed an enhancement in the concentration of holes produced by radiation that are stabilized by the presence of the Tm3+ electron traps. The optimum impurity concentration was determined to be 2%(molar) to give a maximum sensitivity to radiation. In the glass form, the Li2B4O7:Tm is more resistant to radiation damage. In policrystalline form it showed a TL sensitivity four and half times higher than in the glass form. In the policrystalline form the Li2B4O7:Tm TL response is linear for seven orders of magnitude range of dose, with 10-4 Gy being the minimum detectable dose for a 13 mg powder sample. The dosimetric peak in the powder sample appeared at 2880C for a heating rate of 7,50C/s. Tm activation energy was determined to be 1.37 eV with a recombination of order 2.5. For routine dosimetry it was produced a sinterized pellet from 40 mg of Li2B4O7:Tm policrystalline powder that showed the basic and necessary characteristics for its application in several radiation fields. (Author)