Plastic scintillator cone

Plastic scintillator cone which was used by a CERN/Daresbury/Mainz/TRIUMF team in an experiment at the CERN 28 GeV proton synchrotron. Two groups of light guides conveyed any light signals, produced by particles passing through the plastic, to photomultipliers. The cone slid close to a gaseous hydrogen target which received a beam of antiprotons. It allowed through its 4 cm aperture (at the top in the picture) those particles which were aligned along the axis of the target where they may form protonium - a temporary union of a proton and an antiproton. The experiment studied this temporary union by observing the X-rays emitted as protonium 'de-exiles' through its possible energy states.