Apparatus for Precise Measurement of Scintillator Decay Times

A digital system has been built for making precise measurements of scintillator decay times. The approach used is similar to the one developed by Bollinger and Thomas. Time intervals between the start of a gamma-induced scintillation and the detection of a single light photon are measured with a time-to-height converter and stored in a pulse height analyzer. The apparatus has a time resolution of less than 2 nanoseconds, a dynamic range of greater than four decades, and is able to detect both prompt and slow decay components in plastic and liquid scintillators. For all fast scintillators studied, the decay of light intensity over the first decade is approximately exponential; however, measured decay times are shorter than those generally quoted. Results of measurements made on several commercially available scintillators will be presented, including NE 102, Pilot B, Pilot A, and MEL-150C.