How does energy resolution of NaI detecting systems change with increasing gamma ray energy?

The energy resolution of sodium iodide (NaI) detecting systems is influenced by the energy of the gamma rays being detected. As gamma ray energy increases, the energy resolution typically decreases.

Energy resolution refers to the system’s ability to distinguish between two different gamma ray energies and is crucial for accurate spectral analysis. When higher energy gamma rays interact with the NaI crystal, the resulting scintillation light produced is generally less proportional to the energy of the incident gamma ray. This is due to several factors, including the effects of saturation, where the number of light photons produced does not increase linearly with energy beyond a certain point.

In practical terms, as gamma ray energy increases, the statistical fluctuations in the number of scintillation photons collected become more pronounced, leading to a broadened peak in the energy spectrum. This broadening is quantified by an increase in the full width at half maximum (FWHM) of the peak, which reflects poorer energy resolution.

Overall, the profound effect of increasing energy on the resolution highlights the performance limits of NaI detectors in high-energy gamma spectroscopy, reinforcing the importance of considering energy resolution when operating in such contexts.