Scintillation Crystals

Light output (LO) is the coefficient of conversion of ionizing radiation into light energy. Having the highest LO,  NaI(Tl) crystal is the most popular scintillation material. Therefore, LO of NaI(Tl) is taken to be 100%. Light output of other scintillators is determined relative to that of NaI(Tl) (%). LO (Photon/MeV) is the number of visible photons produced in the bulk of scintillator under gamma radiation.
Scintillation Decay time is the time required for scintillation emission to decrease to e-1 of its maximum.
Energy resolution is the full width of distribution, measured at half of its maximum (FWHM), divided by the number of peak channel, and multiplied by 100. Usually Energy resolution is determined by using a 137Cs source. The above description is illustrated in Fig. 1. Energy resolution shows the ability of a detector to distinguish gamma-sources with slightly different energies, which is of great importance for gamma-spectroscopy.
Emission spectrum is the relative number of photons emitted by scintillator as a function of wavelength. The Emission spectrum is shown in Fig. 2. The intensity maximum corresponds to the Imax wavelength shown in the table. For coefficient detection of emitted photons, the maximum of PMT quantum efficiency should coincide with Imax.
Background is a quantity determined as a number of luminescent pulses emitted by radioactive substance within 1 second in the bulk of the scintillator with the weight of 1 kg.
Most scintillation crystals reveal a number of luminescent components. The main component corresponds to Decay time, however less intense and slower ones also exist. Commonly, the strength of these components is estimated by using the intensity of a scintillator’s glow, measured at specified time after the Decay time. Afterglow is the ratio of the intensity measured at this specified time (usually, after 6 ms) to the intensity of the main component measured at Decay time.