Specification for total absorption counter

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The following paragraphs describe the (in 2002 improved) total absorption counter in Hall B.

  • The counter consists of a single 20x20x40 cm3 lead glass block (SF5). The length (40 cm) corresponds to 17 radiation lengths.
  • A single PMT (Hamamatsu R1250) is attached and instrumented with TDC and ADC.
  • The device can only be used at very low beam intensities (~100 pA) and thin bremsstrahlung radiators (~2x10-5 X0) to keep the rate below ~100 kHz (at 35 mV threshold).

Other option: use Cerenkov light produced in a cylinder filled with oil: this allows for higher rates but it is not clear whether an efficiency of 100% (>99.9%) can be achieved.