On the use of NaI scintillation for high stability nuclear decay rate measurements

We demonstrate the linearity and stability of a gamma-ray scintillation detector comprised of a NaI(Tl) crystal and a scientific-grade CMOS camera. After calibration, this detector exhibits excellent linearity more than three decades of activity levels. Because the detector is not counting pulses, no dead-time correction is required. When high activity sources are brought into close proximity to the NaI crystal, several minutes are required for the scintillation to achieve a steady state. On longer time scales, we measure drifts of a few percent over several days. These instabilities have important implications for precision determinations of nuclear decay rate stability.