Organic lyoluminescence dosimetry : its mechanism and its applications
The lyoluminescence (LL) spectra emitted when irradiated carbohydrates were dissolved in pure water can be interpreted as the superposition of emission from singlet oxygen "collisional pairs". The amino acid spectra in pure water are consistent with excited carbonyl emissions. The results therefore provide further evidence that the self-reaction of peroxy radicals is the underlying mechanism of organic LL in pure water. In the presence of sensitisers, the spectra became characteristic of the sensitiser. The factors affecting the accuracy and precision of glutamine lyoluminescence dosimetry (LLD) were investigated. The dependence of the LL yield on the mass of glutamine dissolved, dosemeter irradiation temperature, solvent temperature, and on the storage time both before and after heat treatment (HT) was investigated. Results are presented for measurements in both pure water and terbium (III) nitrate solutions. Two HT's, namely 114°C for 5 and 21 hours, were tried. The shorter HT was more effective at reducing storage time effects. An overall irradiation temperature coefficient of 0.65(±0.05)% per °C above 22°C was determined. The yield is very dependent on the solvent temperature. The participation of glutamine LLD in two IAEA intercomparisons of various high-dose measuring techniques is described and its performance assessed. An overall precision (S.D.) of 5% and a mean error of less than 2% was achieved in estimating the doses given to samples that had been mailed abroad to receive doses in the range 10 Gy - 10 kGy. The application of mannose LLD to clinical dosimetry and glutamine LLD to industrial radiation processing is discussed. The speed of measurement is a major drawback. Commercial luminometers, which are readily available, did not perform very satisfactorily as LL readers. It was concluded that LLD is unlikely, in its present state, to replace the existing dosimetry systems. Finally, a preliminary investigation was performed into the LL properties of halogenated nucleosides.