  The possibilty of performing high-rate calorimetry with a slow scintillator
crystal is studied. In this experimental situation, to avoid pulse pile-up, it
can be necessary to base the energy measurement on only a fraction of the
emitted light, thus spoiling the energy resolution. This effect was
experimentally studied with a BGO crystal and a photomultiplier followed by an
integrator, by measuring the peak amplitude of the signals. The experimental
data show that the energy resolution is exclusively due to the statistical
fluctuations of the number of photoelectrons contributing to the peak
amplitude. When such number is small its fluctuations are even smaller than
those predicted by Poisson statistics. These results were confirmed by a Monte
Carlo simulation which allows to estimate, in a general case, the energy
resolution, given the total number of photoelectrons, the scintillation time
and the integration time.
