Particle detection at cryogenic temperatures with undoped CsI

TL;DR

This study investigates the scintillation properties of undoped CsI at cryogenic temperatures, revealing significant light yield enhancement and similar decay dynamics for alpha and gamma particles, aiding rare-event detection.

Contribution

It provides the first detailed time-resolved scintillation measurements of CsI at cryogenic temperatures, highlighting its potential for particle discrimination in dark matter searches.

Findings

Light yield of CsI increases up to 100 times at cryogenic temperatures.

Alpha to gamma quenching factor exceeds 1 between 10 and 100 K.

Decay time constants are similar for alpha and gamma excitation across temperatures.

Abstract

Scintillation at cryogenic temperatures can give rise to detectors with particle discrimination for rare-event searches such as dark matter detection. We present time-resolved scintillation studies of Caesium Iodide (CsI) under excitation of both alpha and gamma particles over a long acquisition window of 1 ms to fully capture the scintillation decay between room temperature and 4 K. This allows a measurement of the light yield independent of any shaping time of the pulse. We find the light yield of CsI to increase up to two orders of magnitude from that of room temperature at cryogenic temperatures, and the quenching factor of alpha to gamma excitation to exceed 1 over a range of temperatures between 10 and 100 K. We also find the time structure of the emitted light to follow similar exponential decay time constants between alpha and gamma excitation, with the temperature behaviour consistent with a model of self-trapped exciton de-excitation.