Spectral Discrimination of Deposited Gamma-Ray Energies in a Simulated CeBr${}_3$ Scintillator

We show that wavelength measurements of individual detected optical photons may provide additional information about gamma-ray energy deposited in a CeBr${}_3$ crystal when the detected-photon-count distributions overlap for nearby gamma-ray energies. Monoenergetic 662 and 629 keV gammas are used in a Geant4 simulation of a $25\times 25\times 20\mathrm{m}{\mathrm{m}}^3$ CeBr${}_3$ crystal. Assuming a light yield of $6.0\times {10}^4$ photons/MeV, a wavelength-independent photon-detection efficiency of 30%, and a wavelength resolution of ${\sigma }_{\lambda }=40$ nm, we find that the fraction of photons reconstructed above 385 nm gives an event-level separation of $\sim$ 2 standard deviations between the 662 and 629 keV event populations selected within the same $\sim$ 1%-wide detected-photon-count interval. No timing or reconstructed interaction-position information is used. The result demonstrates, within the present simulation model, that event-dependent optical spectra can retain energy information beyond an undifferentiated photon count.