Lead Glass Čerenkov Radiation Photon Spectrometer

A spectrometer for analyzing photons of energies extending up to several Bev has been constructed and used successfully. This instrument essentially consists of a cylinder of glass, 12‐in. diam and 14‐in. long containing 52% of PbO, viewed by four 5‐in. diam photomultipliers. High‐energy photons incident along the spectrometer axis produce electron showers in the transparent high‐Z glass. The total Cerenkov radiation emitted by these electrons and detected by the phototubes is nearly proportional to the energy of the incident photon, from 50 Mev to at least 1.4 Bev. The spectrometer has been calibrated over this range of photon energies by the pulses produced by electrons of the same energies. Above 200 Mev the measured energy resolution of the spectrometer is 30% and is approximately independent of energy. For elimination of incident charged particles during the analysis of γ rays the spectrometer is operated in coincidence with a preceding photon‐identifying counter system.