FLUORESCENCE DECAY TIME MEASUREMENTS OF ORGANIC SCINTILLATORS

Abstract

The time dependence of the fluorescence emission from scintillators has been measured for a number of commonly used organic scintillators under alphaparticle and gamma-ray excitation. A sampling oscilloscope was used to record the pulses obtained from a fast scintillation counter. Using such a system, a gating arrangement can be employed which permits selection of only those scintillation events which deliver a predetermined total charge output from the photomultiplier. Noise within the sampling unit limits the measurements to the main fast components in the fluorescence emission. All of the plastic scintillators exhibit decay times between 2.1 and 4.4 nsec. Stilbene exhibits "particle type" discriminating characteristics with a strong second component in the decay (~35 nsec) appearing under alpha-particle excitation. In addition to the main component in the decay of anthracene, evidence of two shorter components was also found. For all the scintillators tested, the alpha-particle induced scintillation had a slightly longer decay time than the corresponding gamma-ray induced scintillation.