A fast gas ionization calorimeter filled with C3F8 for operation at high counting rates and hard radiation environment

The performance of a gas ionization EM calorimeter with planar electrodes a nd steel absorbers has been studied with a 26.6 GeV/c electron beam at the 70 GeV IHEP accelerator. The design of the calorimeter is optimized for the operation at high counting rates by minimizing the coupling inductance and by choosing rather fast and heavy perfluoroalkane C3F8 (v(dr) = 0.07 mm/ns at a reduced held E/N = 1.0 x 10(-16) V cm(2)). This gas has been used for the first time in calorimetry applications. The total calorimeter thicknes s is approximate to 21X(o). The signal readout has been done by remote 25 O mega low-noise preamplifiers coupled to towers via 25 Omega cable of 4m len gth. The choice of a 25 Omega input impedance provides a complete matching between preamplifier, cable and tower. The studies of the calorimeter consi sted in measuring the signal and noise spectra at different values of HV, A DC gate width and gas pressure. The electron attachment rate in C(3)F8 with a stated purity of 99.99% is quite low (at a given E/N the mean free path of electrons is lambda = 2.2 cm at 1 atm). The intrinsic energy resolution of the calorimeter after noise subtraction is found to be independent of th e gas pressure and equal to approximate to 7% at E = 26.6 GeV/c. (C) 1998 E lsevier Science B.V. All rights reserved.