Quality Assurance on Un-Doped CsI Crystals for the Mu2e Experiment

The Mu2e experiment is constructing a calorimeter consisting of 1,348 un-doped CsI crystals in two disks. Each crystal has a dimension of 34×34×200 mm
³
, and is readout by a large area SiPM array. A series of technical specifications on mechanical and optical parameters was defined according to the calorimeter physics requirements. Pre-production CsI crystals were procured from three firms: Amcrys, Saint-Gobain and SIC. We report the quality assurance on crystal's scintillation properties and their radiation hardness against ionization dose and neutrons. With a fast decay time of about 30 ns and a light output of more than 100 p.e./MeV measured by a bi-alkali PMT, un-doped CsI crystals provide a cost-effective solution for Mu2e.