Design of a Scintiliation Counter K+ Detector for a Bubble Chamlber

A K+ detector is being designed for the Princeton-Pennsylvania Accelerator Rapid Cycling 15" Hydrogen Bubble Chamber which will trigger the photography whenever a K+ is produced in the chamber.1 For the reactions of interest within our energy range, the K+' s produced in the chamber will come to rest in the magnet coils needed for the field in the chamber and in the absorbers which will be placed in the gap between the coils. Plastic scintillators will be sandwiched between coil pancakes and absorber layers, and viewed by 96 2" photomultiplier tubes. We expect to be able to detect all delayed pulses due to K+ decay secondaries triggering at least two layers with delays greater than 7 nsec., which corresponds to 20 per cent of all K+'s produced. The major design problems are connected with economical design of the magnet-scintillation counter system and detection of the pulses delayed only a few nanoseconds in the possible presence of sometimes larger "prompt" pulses in the same counters.