Radical formation in lithium and magnesium oxalate

Lithium oxalate (Li-oxalate: Li2C2O4) and magnesium oxalate (Mg-oxalate: Mg C2O4.2H(2)O) were investigated by electron spin resonance (ESR) spectroscop y as new ESR dosimeter materials. The ESR spectra of Li- and Mg-oxalates ir radiated by gamma -rays have a singlet with a spectroscopic splitting facto r (g-factor) of g = 2.0043 +/- 0.0004 and are ascribed to a self-trapped ho le, the oxalate radical C2O4-. A broad signal formed by high dose irradiati on is considered to be due to the zero field fine structure splitting, DS2 (Dg beta congruent to 0.65 mT) for the triplet state (S = 1) of a dimer of C2O4- or a pair of electron and hole centers. The response to the gamma -ra y dose and thermal stability as well as the effect of illumination have bee n studied with respect to using these materials as ESR dosimeter elements. The radical formation efficiencies (G-value) for Li- and Mg-oxalates were 0 .4+/- 0.1 and 0.21 +/- 0.06 and the activation energies (E) from the Arrhen ius plot were 1.16 +/- 0.24 eV and 1.28 +/- 0.26 eV, respectively. These le ad to the respective lifetimes of 2.6 +/- 0.9 and 3.2 +/- 1.1 years at 25 d egreesC, which are sufficient for practical dosimetry.