A hodoscope spectrometer for high-energy photons

Abstract A scintillation-counter hodoscope spectrometer developed at IHEP to detect high-energy photons is described. The detector can simultaneously measure the position (to 2 mm) and energy (5–10%) of several photons. The device is made with 648 scintillation counters, arranged to form hodoscopes and sandwiched between layers of iron converter. The useful area of the spectrometer is about 1 m 2 . Pulse-height analysis is performed on each of the 648 counters with 12-bit ADCs. Photon position is determined using the center of gravity of the shower amplitudes in the hodoscope counters. To eliminate ambiguities in multi-photon events, the showers are measured in three 120° projections. The total thickness of the spectrometer is 20 r.l. of steel in the beam direction. This provides total absorption of photons and electrons with an energy up to 1000 GeV. The characteristics of the spectrometer as used in experiments at the 70 GeV IHEP accelerator are described.