Reducing NaI(Tl) Detector Spectrum Shift by Optimizing Pulse Integration Time

NaI(Tl) spectrometry is widely used in many areas for gamma-ray detection. It can be used for both activity measurement and isotope identification. However, the light generation of NaI(Tl) and photomultiplier tube (PMT) is sensitive to temperature changes, which lead to spectrum shift. Several calibration methods have been proposed, but they are complicated. In this article, we developed an NaI(Tl) spectrometry for indoor monitoring and studied the temperature influences from 5 °C to 35 °C using a
²²
Na source. We found that the severity of the temperature-dependent spectrum shift can be reduced by using fewer integration points (i.e., short integration time) for energy calculation. The spectrum shift can be reduced from 18.1% to 3.3% for 511 keV and from 18.0% to 3.7% for 1274 keV by using an integration time of 385 ns instead of 1.23 μs . In conclusion, the spectrum shift phenomenon can be reduced by reducing integration time. Thus, the indoor monitoring NaI(Tl) spectrometry might work properly for isotope identification without a complicated calibration procedure.