Lyoluminescence of irradiated organic compounds in aqueous and non-aqueous solvents
Lyoluminescence (LL) of the phosphors glutamine and mannose was used to determine instrument stability, reproducibility of readings, sensitivity and lowest detectable dose in order to evaluate the performance of the Aberdeen LL Research Reader (before and after modifications) and compare it with commercially available luminometers. The dependence of the LL yield on mass of dissolved glutamine, the sample's irradiation temperature, and solvent temperature were investigated and correction factors determined. Heat treatment was found to remove the dependence on pre- and post-irradiation storage time. Using aqueous LL dosimetry of glutamine, unknown doses in the range 10Gy to 3kGy were determined with overall accuracy and precision of 2% and 5% respectively during the 1982 IAEA Dose Intercomparison trials. Factors affecting the LL of mannose in water and methanol were compared, and a 20-fold increase in LL yield was reported using the latter solvent. Various attempts to enhance the LL yield from glutamine and mannose were made: Enhancements, of up to 105 times, caused by the oxidation of luminol, lucigenin, lophine and trichlorophenol oxalate by the primary species in LL were observed, but increased background readings due to self-glow caused there to be no advantage in overall sensitivity. Enhancement factors (EF) up to 100 were obtained using glutamine LL in free and chelated rare earth ion solutions, as a result of intermolecular energy transfer from excited organic molecules in solution. However, the enhancement was found to be dose dependent. By employing dibromoanthracene sulphonate, rubrene, eosin and reduced lucigenin, all of which respond to singlet oxygen, EF of up to 10 were achieved in LL of mannose. Finally, as the use of aqueous solutions was found to severely limit the possible phosphor/enhancer combinations, the LL of some carboxylic acids in alcoholic media was investigated. These were found to be less sensitive LL phosphors than either mannose or glutamine.