Energy resolution and other properties of CsI(Tl) crystals

We plan to use an array of 9600 CsI(Tl) crystals as the electromagnetic (EM) shower detector for the asymmetric B-Factory at KEK. In order to determine the length of a crystal, we studied energy resolution, electron/pion separation, and other properties of 25 cm and 30 cm long CsI(Tl) crystals of a 3 X 3 matrix at GeV energy region. When electrons with energy of 1 GeV (4 GeV) is injected into the crystals, the energy resolution of 25 cm and 30 cm length is 2.7% (3.0%) and 2.4% (1.8%), respectively. The misidentification of a pion as an electron is less than 0.5% for energies above 1 GeV.