A system for controlling photomultiplier gain drift is disclosed. According to one aspect, the system includes first means for measuring a noise signal of the photomultiplier, the first means configured emit a measurement signal representative of the photomultiplier's noise signal. The system further includes second means for maintaining the measured noise signal at a constant level, based on the measurement signal. The disclosed embodiments apply to stabilization of the gain of photomultipliers and, more specifically, to stabilization of neutron measurement systems using photomultipliers.