The energy resolution, ∆E/E, of the full energy peak measured with a scintillator coupled to a photomultiplier can be written as [8]: (∆E/E)2 = (δsc)2 + (δp)2 + (δst)2 (1) where δsc is the intrinsic resolution of the crystal, δp is the transfer resolution and δst is the PMT statistical contribution to the resolution. The statistical uncertainty of the signal from the PMT is described, as: δst = 2.35 × 1/N1/2 × (1 + ε)1/2 (2) where N is the number of photoelectrons and ε is the variance of the electron multiplier gain. In the case of the XP3212 this was determined as 0.12, analyzing the single photoelectron peak. The transfer component, δp, in modern scintillation detectors is negligible compared to the other components of the energy resolution [8].