How much light from rectangular scintillation counters?

Abstract

Theoretical calculations have been made of the efficiency and uniformity of light collection at one end of a large rectangular liquid scintillation counter (80x20x18 cm). Three different arrangements were considered; (1) a system in which all surfaces of the counter other than the collecting surface were transparent to permit total internal reflection, (2) a similar system with a mirror placed close to the end opposite the collecting surface and (3) a system in which external reflectors were placed close to surfaces other than the collecting surface. In all cases, the effects of attenuation of light in the counter medium, inefficient total internal reflection and the reflectivities of external reflectors were considered and illustrated for selected values of these parameters. In an experimental counter of the same dimensions, the amplitude of the spectrum of a collimated 42-K source was used to measure the relative efficiencies of light collection for various reflector arrangements. In general the experimental values agreed with theory and the non-uniformity of response was within the predicted range. It is estimated that about 30% of scintillation light can be collected at one end of such a counter, with a non-uniformity not greater than 10%, if magnesium oxide is used as the external reflector at all other surfaces.