1. A method comprising: coupling a charge calibrator to a nuclear energy measurement system; receiving a user input at said charge calibrator; executing a Gaussian random number generator algorithm in a processor of the charge calibrator to produce a digital output comprising a Gaussian random number distribution having at least one characteristic established in response to said user input, wherein said digital output simulates a digital output corresponding to an output pulse of a photomultiplier representative of a scintillating light pulse received by the photomultiplier; and calibrating said nuclear energy measurement system over a plurality of energy levels that include a lower energy level and an upper energy level that are separated by at least 450 keV/photon, wherein calibrating is performed using said charge calibrator.