Present status of radiation damage effects in plastic scintillators and fibers

Summary form only given. Studies of plastic scintillators have shown that high dose rate exposures almost always underestimate the radiation-induced damage at low dose rates. The degree of excess damage depends in a complex manner on the dose rate, temperature, and oxygen partial pressure. Excess damage is confined to a few-millimeter-thick surface zone, a finding of especial importance for the use of scintillating or wave-shifting fibers. An important consequence of these investigations is that it is not known how to carry out accelerated aging tests. It has also been shown that the thermal and atmospheric history of a particular piece of scintillator is relevant to the amount of damage incurred by radiation. A scintillator which has been heated or kept in inert gas for several days prior to irradiation is more easily damaged. Because the chemical mechanisms which are responsible for radiation-induced color centers in the common bases polystyrene and polyvinyltoluene remain to be clarified, the best chance for near-term progress in the creation of more radiation-tolerant scintillators may be in finding new fluors which emit at longer wavelengths thus circumventing the color centers