Production and suppression of delayed light in NaI

TL;DR

This study explores the phenomenon of delayed light emission in NaI(Tl) crystals, examining its characteristics, causes, and suppression methods, which is relevant for understanding detector signals in dark matter experiments.

Contribution

It provides experimental evidence of delayed light in NaI(Tl) crystals and demonstrates suppression of this emission using red light, offering insights into detector signal interpretation.

Findings

Delayed light emission occurs after UV and gamma irradiation.

Delayed emission mainly consists of uncorrelated single photons.

Red light irradiation suppresses delayed photon emission.

Abstract

We investigate a hypothesis that energy accumulation and the subsequent release in NaI(Tl) may lead to pulse-like events in the few-keV energy regime, a phenomenon suggested by the crystal manufacturing company Saint-Gobain, who provided the crystals for DAMA-LIBRA. While we observed delayed long-lasting light emission in a 3" NaI(Tl) crystal after exposing it to UV light, the delayed light consists primarily of single photons that are uncorrelated with each other. We also observe delayed light emission in NaI(Tl) following gamma radiation and large ionization events like cosmic-ray muons. We found that irradiating the crystal with red light after UV exposure significantly suppressed delayed photon emissions.