WA80 BGO calorimetry electronics

This paper describes instrumentation designed for BGO scintillator-based calorimetry of particles covering a very wide range of energies (from less than 50 MeV to 50 GeV). The instrumentation was designed to have a measurement accuracy of 0.1% over as much of the energy range as possible so the energy resolution of BGO would be the limiting factor. Two 1.5-cm² photodiodes were used per 2.5 cm × 2.5 cm × 25 cm BGO crystal. Both a charge-sensitive preamplifier and a pulse processor were developed specifically for the needs of the WA80 experiment. The preamplifier was designed for high detector capacitance (100 to 700 pF), low integral and differential non-linearity and low power consumption (200 mW). The pulse processor is a time-invariant shaping amplifier with integral peak-detect-and-hold and automatic gain selection circuits. The amplifier uses quasi-triangular shaping with 4 μs peaking time, and the hold circuit is gated with a fast first level trigger. The preamplifier and pulse processor combination has more than 20 bits of effective resolution when used with an external 12-bit ADC. An array of BGO instrumented with 100 preamplifiers and pulse processors was used in beam tests at CERN. Preliminary results from those tests are presented.