Intrinsic energy resolution of NaI(Tl)

The light output for ∅10 mm×10 mm and ∅75 mm×75 mm NaI(Tl) crystals and energy resolution were measured for γ-ray energies ranging from 16–1333 keV. These measurements enabled the observation of the light yield nonproportionality behavior and allowed the determination of the intrinsic resolution after correcting for the measured resolution for photomultiplier tube (PMT) statistics. The intrinsic resolution was then compared with the nonproportionality component. The latter was calculated using measured electron response, Monte Carlo N Particle code (MCNP4B), and the simplified cascade sequence for NaI(Tl). This comparison allowed the identification of the intrinsic resolution component associated with δ-rays. Consequently, it was shown that the δ-ray component is the most dominant component of the NaI(Tl) intrinsic resolution.