  Using highly monochromatic synchrotron X-rays in the energy range from 10.5
keV to 100 keV the temperature dependence of nonproportionality and energy
resolution of LaBr3 scintillators doped with 5% Ce3+ were studied at 80K, 295K,
and 450K. Improvement of the proportionality and better energy resolution was
observed on lowering the temperature. This effect suggests that the already
outstanding energy resolution of LaBr3:Ce can be improved even further. It also
may provide new clues to better understand the processes that cause
nonproportionality of inorganic scintillator response.
