Increasing the Light Collection Efficiency of Scintillation Counters

Abstract

A systematic study was made of methods of increasing the light collection efficiency of scintillation counters. Various reflectors, surface treatment of the scintillator, relative geometries of scintillator and photodiode, and light pipes were tried, using plastic scintillator cubes, 3 and 6 in. on a side, and right circular cylinders, 3 in. in diameter by 3 in. in length and 6 in. in diameter by 6 in. in length. The maximum factors by which light output could be increased, relative to a polished scintillator, were about 2.8 for 6‐in. scintillators and 3.3 for 3‐in. scintillators without the use of light pipes, and 5.0 for a 3‐in. scintillator with light pipe. The fraction of light trapped in a right circular cylinder by total internal reflection is derived as a function of index of refraction, as are the percentages of light coming out the ends and sides of a cylinder.