Čerenkov Counter Flux Measurement of Cosmic-Ray Alphas at 41°

A Čerenkov counter inside a Geiger counter telescope was flown by balloon to a residual atmospheric depth of 16 g/${\mathrm{cm}}^2$. The purpose of the experiment was to measure the flux of cosmic-ray alpha particles and to investigate the usefulness of a Čerenkov counter for flux measurements on the more heavily charged cosmicray components. A Čerenkov counter was used because of its inherent discrimination against slow secondary particles. The pulse height distribution obtained showed a partially resolved peak at approximately 4 $h_0$, where $h_0$ is the mean pulse height corresponding to a fast proton. This is experimental confirmation of the $Z^2$ dependence for Čerenkov radiation. There were 3024 events which gave pulse heights corresponding to alphas. There is evidence that 451 were due to side showers, 651 were due to nuclear interactions, an additional 478 were due to either side showers or interactions, and 1444 were due to primary alphas. This leads to the value 99±16 particles/${\mathrm{m}}^2$-steradian-second, as the extrapolated flux at the top of the atmosphere. There is also an indication of peaks corresponding to carbon and oxygen. There is evidence that the geometry factor of the telescope was appreciably increased for the heavy components due to the action of delta rays.