Light Collection from Long Thin Scintillator Rods and Optical Coupling

In nuclear detection, it is often advantageous to detect the nuclear events occurring at widely separated points and to route this information to a central location. This problem was encountered in the design of a nuclear gaging system for the reaction control tanks of the Apollo vehicle. An evaluation of system requirements showed that a design using a multiplier phototube and an array of scintillator rods offered optimum efficiency, weight and accuracy. This approach demands that the scintillator rods act both as gamma detectors and as light pipes to conduct the light to the phototube. An investigation of the light conducting properties of various scintillator materials as a function of rod length, diameter, shape and surface conditions is herein reported. The light piping properties of several materials and geometries have been explored both experimentally1,2 and theoretically3,4. Scintillation materials have been used as light pipes in several instances,5,6 although usually where environmental conditions make more direct means infeasible (for instance, where intense magnetic fields would effect the phototube).