Tagging System for High Energy Photons

Abstract

An apparatus has been built to determine the energy of each photon in a bremsstrahlung spectrum which produces an interaction of interest in a hydrogen target. The technique was applied specifically to charged pion photoproduction with photons of 2 to 5 BeV. The tagging system utilized a monoenergetic (to ± 1%) positron beam which produced photons and associated recoil positrons in a thin radiator. The recoil positrons were momentum analyzed and detected by a 19‐counter hodoscope. The difference between the energies of an incident and a recoil positron is the photon energy, and this was determined to ±2.5%. Since the photon beam is relatively weak, the interactions it produces must be detected with good efficiency. Such a large‐solid‐angle spark chamber, magnet, and counter system, which was used to measure the photoproduced pions, is also described.