  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.
