Metal ion-organic compound for high sensitive ESR dosimetry

Abstract

A systematic study to find a tissue equivalent and high sensitive dosimeter material has been made to stimulate the field of ESR dosimetry. Lithium acetate dihydrate (Li-Ac·2H 2O:CH 3COOLi·2H 2O) and lithium phosphate (Li-phosphate:Li 3PO 4) were irradiated by γ-rays to study radicals with (ESR) in addition to magnesium lactate (Mg-lactate (CH 3CH(OH)COO) 2Mg) doped with nominal pure lithium lactate (Mg(Li)-lactate) and lithium lactate (CH 3CH(OH)COOLi) doped with Mg-lactate (Li(Mg)-lactate). A triplet spectrum with intensity ratio of 1:2:1 in Li-Ac·2H 2O was ascribed to acetate radical which has g=2.0031±0.0004 and hyperfine splitting of A/ gβ=2.12±0.1 mT. The Li-phosphate spectrum shows splitting due to anisotropic g-factors of g ‖=2.0190±0.0005 and g ⊥=1.9974±0.0004. Quartet spectra with the intensity ratio of 1:3:3:1 in Mg(Li)-lactate and Li(Mg)-lactate were ascribed to lactate radicals with g-factors of 2.0032 ± 0.0004 and 2.0029 ± 0.0004 and the intensity ratio of 1:3:3:1 and A/ gβ=1.92±0.06 and 1.82 ± 0.06 mT, respectively. The response to γ-ray dose and the thermal stability as well as the effect of UV-illumination have been studied. The obtained number of free radicals per 100 eV ( G-values) were 0.4 ± 0.13, 1.02 ± 0.31, 1.35 ± 0.35 and 0.78 ± 0 for Li-Ac.2H 2O, Li-phosphate, Mg(Li)-lactate, and Li(Mg)-lactate, respectively. The lifetimes were estimated from Arrhenius plots to be approximately 2.0 ± 0.6, 50.7 ± 20 and 10 ± 3.5 years for Li-phosphate, Mg(Li)-lactate and Li(Mg)-lactate, respectively. The lifetime for Li-Ac·2H 2O cannot be estimated because of the decomposition by heating.