A detailed test of a BSO calorimeter with 100-800Â MeV positrons

A performance test has been made for an electro-magnetic calorimeter prototype comprised four identical BSO crystals arranged in a 2×2 matrix by utilizing a positron beam in the energy range from 100 to 800 MeV. The size of each crystal is 40×40×210 mm3. This is the world's largest BSO single crystal ever used as a photon detector. The obtained energy resolution is (σE/E)2=((1.71%±0.03%)/E)2+(1.12%±0.08%)2 at room temperature, where E is the incident positron energy given in GeV. A BGO calorimeter having the same geometry has been employed in the performance test for comparison. The basic scintillation characteristics of BSO crystals measured without the beam are also presented.