Estimation of Fano factors in inorganic scintillators

The correlation between outputs of two photodetectors on opposite faces of a scintillator crystal was used to deduce the Fano factor of the photoelectrons and the photons of scintillation light for different scintillators. The Fano factor of an integer-valued random process is defined as the ratio of its variance to its mean. A Poisson process has a Fano factor of one and a sub-Poisson process has a Fano factor of less than one. Correlation measurements were taken for a number of scintillators including YAP and SrI₂, which have excellent energy resolution but very different light outputs. Measurements were also take for CsI:Na. From these measurements, the Fano factors for the photoelectrons as well as the optical photons were estimated.