A RICH counter for identifying antimatter and light isotopes in the cosmic radiation

A ring imaging Cherenkov (RICH) counter using a solid radiator of NaF is described. It will be an important part of a balloon borne magnet spectrometer to measure the flux of antiprotons and light nuclei in cosmic radiation. For β=1 particles of unit charge (normal incidence), 20 photoelectrons per event are detected resulting in a resolution of the reconstructed Cherenkov angle of 5 mrad (r.m.s.). For ¹⁴N nuclei more than 1000 photoelectrons are detected per event (β=0.86, normal incidence). Together with a time-of-flight system and an electromagnetic calorimeter it is capable of identifying, in the energy region 0.3-5 GeV, antiprotons and positrons in the presence of a large background. To a good accuracy it measures both the charge and the velocity of the cosmic rays, and can be used to identify different isotopes with Z:1-10 in the energy range of 0.3-3 GeV/nucleon. This detector is planned to fly for 24 hours in the New Mexico State University Balloon Borne Magnet Facility in July 1994 from Lynn Lake in Canada