LOW-DOSE RATE EVALUATIONS OF LONG PLASTIC SCINTILLATOR PLATES AND BIRCON G2-DOPED WAVELENGTH SHIFTING FIBERS

Electromagnetic calorimeter modules are being constructed for the CEBA F Large Acceptance Spectrometer that will utilize plastic plate scinti llators that can be over 4 meters in length. At shower maximum, it is expected that up to 100 Gray may be deposited over a ten year lifetime in the detector elements. Although it is believed that PVT-based scin tillators are radiation-hard at that level, the large size of the plat es motivated an ageing test of a 2 meter long sample so as to gain a r ealistic estimate of the loss in intrinsic light output and especially in attenuation performance of the chosen scintillator (Bicron BC412). A test setup was designed so that the sample was irradiated (by a Co- 60 line source) at a rate sufficiently low (0.5 Gray/hr) to allow comp lete diffusion of oxygen into the material during the irradiation. Add itionally, in order to ensure complete diffusion and to gain a pessimi stic estimate of damage, a pure oxygen atmosphere was circulated throu gh the sample container during the irradiation, and the total dose was increased to a total of 160 Gray. Within the same setup, tests were a lso made of two additional materials: (1) a 1 meter long sample of an uniquely bright, fast green scintillator with superior attenuation pro perties, and (2) a customized acrylic scintillator (with a high doping level of fluors) read out by embedded (into smooth grooves cut into t he surface of the scintillator) wavelength shifting fibers doped with the same green fluor as the aforementioned scintillator. The data indi cates that the BC412 shows no loss in intrinsic light output, but does have an attenuation loss amounting to 10% at 1 meter and 16% at 2 met ers. The fast green scintillator (and fibers) showed no damage. When r ead out by WLS fibers, the acrylic scintillator displayed a loss in in trinsic light output, but no change in attenuation.