Methods for improving the accuracy of glutamine lyoluminescence dosimetry

Abstract

The dependence of the lyoluminescence (LL) yield on the mass of dissolved glutamine, the sample irradiation temperature and solvent temperature, and the storage time both before and after heat treatment (HT) was investigated. Results are presented for measurements in both pure water and in terbium(III) nitrate solutions. Terbium(III) ions enhance glutamine's LL yield. HT's of 114°C for 5 and 21 h were tried. Irradiation of glutamine produces two alkyl free radicals; one named Ṙ 1, more stable than Ṙ 1. It is believed that Ṙ 1 reduces the LL yield. The gradual decay of Ṙ 1 during storage of untreated samples results in an increased LL yield. The rate of this increase depends on dose. Heat treatment removes the dependence of the yield on storage time and increases the yield (by a factor of approximately 2). It is suggested that heat treatment reduces Ṙ 1 to the same final concentration in all samples given the same dose. The shorter heat treatment which resulted in a variation of 4% between samples stored for up to 87 days before HT and up to 86 days after HT, gave better results than the longer treatment. The yield of treated samples increases linearly with irradiation temperature (between 14 and 39°C) by 0.63 (±0.03)% and 0.65 (±0.04)% per °C above 22°C for LL readings taken in pure water and terbium nitrate solutions respectively. No such correlation was found for untreated samples. Limiting the range of (a) the mass of glutamine dissolved to ±0.5 mg and (b) the temperature of the solvent to ±0.1 °C reduces the variation in yield due to each factor to less than 0.4% using either water or terbium nitrate as the solvent.