Specification for broad-band tagging hodoscope

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The fixed-array hodoscope consists of 180 scintillators distributed over a length of 11.2 m at a distance of 30 cm from the focal plane of the two-magnet system.

Tagging range (for a 12 GeV electron beam):

  • Photons between 3.0 GeV and 9.0 GeV: detector positions correspond to 60 MeV steps in Eγ with 50% sampling, i.e. the counter widths correspond to 30 MeV bites resulting in ~0.8-1.1 MHz per counter at 107 γ/sec on target;
  • Photons between 9.0 GeV and 11.4 GeV: detector positions correspond to 30 MeV steps in photon energy resulting in ~400 kHz per counter at 107 γ/sec on target.

Count rates in the high-energy range allow for operation at 108 γ/sec on target. All counters will be mounted at angles such that they face normal to the path of the scattered electrons.


     thickness         5mm
     length           30mm
     width (quantity) 30(2), 25(3), 20(6), 15(15), 10(14), 
                      8(13), 7(9), 5(54), 4(24)


     1" tubes with magnetic shields

Readout electronics

     CFDs, TDCs, Scalers


     timing:  rms ~100-150 psec
     energy:  20 MeV (above 9.0 GeV photon energy)
              30 MeV (sampled - below 9.0 GeV photon energy)