An annular parallel plate avalanche counter for heavy-ion γ-ray coincidence measurements

The characteristics and performance of an annular parallel plate avalanche counter (APPAC) developed for performing heavy ion nuclear physics experiments are presented. The main motive of developing this detector system is to perform Coulomb excitation (Coulex) experiments using particle–γ coincidence technique. The Coulex measurements are performed with APPAC and clover germanium detectors. The APPAC has a two electrode geometry and provides information about the scattering angles of the reaction products, which along with their velocity and/or energy information is used for correcting Doppler energy shift of γ-ray events coming from the in-flight decay of reaction products. The detector has an active area of ∼ 410 cm ² and provides scattering angle information in two coordinates namely polar angle θ and azimuthal angle ϕ. The ϕ resolution is fixed at 22.5° and the θ resolution for the present experimental configuration is about 0.6°. Average rise times of the signals after amplification was observed to be 5 ns. During the experiments, the detector could handle heavy ion count rates of about 25 x 10 ⁴ pps without any deterioration in the quality of signals.