A "dwarf ball": Design, instrumentation, and response characteristics of a 4π light charged-particle multidetector system

A 4π light charged-particle spectrometer is described. The spectrometer consist of 72 fast-low plastic scintillator phoswiches closely packed in a 4π arrangement. The device is small enough to be enclosed in the spin spectrometer scattering chamber. For each detector that fires, the fast ΔE and slow E pulse heights and a time for each group of 16 detectors are recorded. From this information protons and α particles can be identified and their energies measured over a large dynamic range. The geometry, construction, electronics and data acquisition system are discussed. Examples are given of the performance of this spectrometer from an experiment in which Si (ΔE, E) heavy-ion telescopes were used as event triggers and the spin spectrometer detected γ rays and neutrons.