A long scintillation counter for precise measurement of time of flight and impact position

Plastic scintillator counters made of long slabs (200×20 cm 2 ) of different thickness have been tested with 120 cm long plexiglas light guides coupled to 58 AVP photomultipliers. The accuracies achieved in measuring the time of flight of 600 MeV/ c protons, which hit the counter at different distances from the photo-multiplier, range from 350 to 450 ps fwhh. The impact position of the particles is determined along the counter by the time difference, as measured from the two opposite ends, with an accuracy ranging from 4.5 to 5.5 cm fwhh.