Specification for total absorption counter
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.