Radiation damage of wavelength shifters and its recovery in the presence of oxygen

The radiation damage induced by γ-rays in wavelength shifters was investigated systematically at doses of 10$^3$–10$^5$ Gy. The reduction of primary light yield and transmission was measured using an UV flash lamp and a Beckman spectrometer. Strong recovery of the radiation damage was observed within one year, when the samples were stored in the presence of oxygen. It is shown that the recovery effects can be described quantitatively in the frame of a diffusion model