Longitudinal uniformity, time performance and irradiation test of pure CsI crystals

TL;DR

This study evaluates the performance, uniformity, timing, and radiation hardness of pure CsI crystals as an alternative to BaF2 for the Mu2e calorimeter, demonstrating promising light yield, uniformity, and radiation resilience.

Contribution

It provides comprehensive characterization of pure CsI crystals, including light yield, uniformity, timing resolution, and radiation hardness, for calorimeter applications.

Findings

Light yield of ~100-150 p.e./MeV depending on wrapping and coupling

Timing resolution around 330-440 ps with optical grease

Radiation dose of 900 Gy causes 33% LY decrease, LRU unchanged

Abstract

To study an alternative to BaF2, as the crystal choice for the Mu2e calorimeter, thirteen pure CsI crystals from Opto Materials and ISMA producers have been characterized by determining their light yield (LY) and longitudinal response uniformity (LRU), when read with a UV extended PMT. The crystals show a LY of ~ 100 p.e./MeV (~ 150 p.e./MeV) when wrapped with Tyvek and coupled to the PMT without (with) optical grease. The LRU is well represented by a linear slope that is on average around -0.6 %/cm. The timing performances of the Opto Materials crystal, read with a UV extended MPPC, have been evaluated with minimum ionizing particles. A timing resolution of ~ 330 ps (~ 440 ps) is achieved when connecting the photosensor to the MPPC with (without) optical grease. The crystal radiation hardness to a ionization dose has also been studied for one pure CsI crystal from SICCAS. After exposing it to a dose of 900 Gy, a decrease of 33% in the LY is observed while the LRU remains unchanged.