Investigation of the cryogenic scintillation of pure and doped sodium-iodine

TL;DR

This study explores the cryogenic scintillation properties of pure and doped sodium iodide crystals, revealing significant temperature-dependent light yield increases and changes in scintillation dynamics relevant for low-temperature detector applications.

Contribution

It provides detailed measurements of scintillation light yield, quenching factors, and time constants of sodium iodide crystals at cryogenic temperatures, highlighting their potential and challenges for cryogenic detection.

Findings

Light yield increases by a factor of 30 at 60K for pure sodium iodide.

Doped sodium iodide stabilizes at 40 photons/keV at low temperatures.

Quenching factor stabilizes around 0.7 below 50K.

Abstract

We have studied the scintillation of pure and doped sodium iodide crystals handled in low humidity conditions under external $\alpha$ and $\gamma$ excitation from room temperature down to 4K. The light yield of pure sodium iodide was seen to increase at low temperatures by a factor 30 compared to room temperature, up to a maximum of 40 photons/keV under $\gamma$ excitation at 60K, stabilizing to 30 photons/keV at lower temperatures. Thallium doped sodium iodide fluctuates by 20% around the room temperature value, stabilizing at 40 photons/keV at low temperature. $\alpha / \gamma$ quenching factor stabilizes at roughly 0.7 for both materials beneath 50K. Time constants of both materials slow greatly at low temperature, reaching tens of microseconds. Cryogenic applications of these materials are complexified by their mechanical fragility and hygroscopicity.