Temperature behavior of NaI(Tl) scintillation detectors

It is a familiar fact that the total measured light yield of NaI(Tl) detectors is a nonlinear function of temperature. Here we present new experimental data for the temperature behavior of doped NaI(Tl) scintillators that instead shows a linear dependence of the light output over a wide temperature range—including that for outdoor applications. The shape of the light pulse shows, in general, two decay processes: a single dominant process (one decay-time constant) above the room temperature and two processes (two decay-time constants) below the room temperature. We show that the redistribution of the intensities between the two processes is temperature dependent; the second (slow) decay component is negligible at room temperatures, but by −20 °C, it contributes up to 40% of the total light and has a duration of several microseconds. We discuss the profound effect this new understanding of the light output has on the pulse-height analysis instrumentation. We introduce a theoretical model to explain the experimental results. In addition, we describe a unique technique for correcting both amplitude and shape temperature changes inside the NaI(Tl) detector package.