  The Mu2e experiment is constructing a calorimeter consisting of 1,348 undoped
CsI crystals in two disks. Each crystal has a dimension of 34 x 34 x 200 mm,
and is readout by a large area silicon PMT array. A series of technical
specifications was defined according to physics requirements. Preproduction CsI
crystals were procured from three firms: Amcrys, Saint-Gobain and Shanghai
Institute of Ceramics. 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 30 ns and a light output of more than
100 p.e./MeV measured with a bi-alkali PMT, undoped CsI crystals provide a
cost-effective solution for the Mu2e experiment.
