A Study Of Epoxide Resin Based Scintillators

The object of this study was to examine the feasibility for the production of commercially viable scintillators, and to investigate the mechanism of energy transfer to enable maximum efficiency to be achieved. Various concentrations of the aliphatic amine hardener XD 716 (125) (a polyoxypropyleneamine) were used to cross-link resin MY 790 (adistilled diglycidylether of bisphenol-A resin of equivalent weight 190). Clear, colourless castings were obtained, with the requisite physical properties; shrinkage less than 5%, and the refractive index about 1.46. Of the various primary solutes studied, PPO (2,5-diphenyloxazole) was found to be the most suitable, in terms of light output under Strontium-90 beta-particle irradiation, with high solubility in the epoxide resin. Scintillators containing the secondary solute bis-MSB (1,4-di-(2-methylstyryl)-benzene) gave the highest light output under Strontium-90 beta-particle irradiation, when measured relative to a polyvinyltoluene-based scintillator NE 102A, (136 Excimer fluorescence was observed from epoxide resin scintillators containing PPO at all PPO concentrations employed, and irrespective of amine or naphthalene concentration. This accounts for the concentration quenching observed under beta-particle irradiation. Non-fluorescent exciplex formation between naphthalene and the polyoxypropyleneamine curing agent satisfactorily explains the quenching observed when naphthalene was added to these scintillators. Energy transfer was studied qualitatively by fluorescence decay time measurements using the method of Swank and Buck. 20) It was found that efficient non-radiative energy transfer occurred from the cured epoxide resin to PPO, but that the addition of naphthalene to these systems prevented this type of energy transfer. Energy transfer from the cured epoxide resin to PPO is described satisfactorily by Foérster-type expressions.(77-82) Efficiencies derived from these expressions compare favourably with those obtained -from energy transfer data. R_, the critical transfer distance at which energy transfer and spontaneous deactivation are of equal probability was found to be between 2.5 - 3.5 nm.