Observation of ring-imaging Cherenkov photons with an image intensifier

We have constructed a prototype of a ring-imaging Cherenkov detector based on the idea that single photons can be directly detected with an image intensifier coupled with a CCD camera. A test using high-energy electron beams was performed with a 2 m long gas radiator at 1 atm. We could successfully see clear Cherenkov rings composed of 21 photons on the average per single event with a Freon-12 gas radiator, and of 12 photons with a nitrogen radiator. (orig.)