  One contribution to the time resolution of a scintillation detector is the
signal time spread due to path length variations of the detected photons from a
point source. In an experimental study a rectangular scintillator was excited
by means of a fast pulsed ultraviolet laser at different positions along its
longitudinal axis. Timing measurements with a photomultiplier tube in a
detection plane displaced from the scintillator end face showed a correlation
between signal time and tube position indicating only a small distortion of
photon angles during transmission. The data is in good agreement with a Monte
Carlo simulation used to compute the average photon angle with respect to the
detection plane and the average propagation time. Limitations on timing
performance that arise from propagation time dispersion are expected for long
and thin scintillators used in future particle identification systems.
