RESPONSE OF PURE CSI TO CHARGED PIONS IN THE INTERMEDIATE-ENERGY REGION

The response of a scintillation detector array consisting of 7 pure Cs I crystals with a thickness of 13.5 radiation lengths has been measure d to electrons, positrons and charged pions with momenta ranging from 250 to 1000 MeV/c. For electrons and positrons the detector provides a very linear response to the incident energy. High energy charged pion s make a peak at around 150 MeV corresponding to the ionization energy loss. In addition to the peak, comparable yields which are caused by nuclear reactions are distributed up to the maximum available energy a nd form a broad bump. The shape of the broad bump for positive pions i s different from that for negative pions with the same momentum. A sim ulation with a GEANT program cannot reproduce the shape of the broad b ump.