Measurement of Multiply Charged Cosmic Rays by a New Technique

The Čerenkov effect has been applied to the problem of determining the charge of cosmic rays. Cloud chamber photographs have been obtained of the events that caused large signals from a thin Čerenkov counter during a balloon flight which carried the apparatus above most of the atmosphere. They show that the Čerenkov counter was notably effective at discriminating against the background effects that plague counter measurements on the charge spectrum of cosmic rays, for a relatively large proportion of the signals were caused by single heavily ionizing particles. The theory of the Čerenkov effect associates a lower velocity limit with the signal amplitude requirement that those particles met. Their ionization was determined well enough to classify particles of such velocity as having $Z=2\mathrm{}$ or $Z>\mathrm{}2\mathrm{}$ with considerable certainty. The vertical flux of doubly charged particles with kinetic energy> (610±100) Mev/nucleon beneath 17 g/${\mathrm{cm}}^2$ of atmosphere and 13 g/${\mathrm{cm}}^2$ of local matter is found to be (79±11)/${\mathrm{m}}^2$ sec steradian. That result and currently accepted assumptions concerning absorption imply the value (135±20)/${\mathrm{m}}^2$ sec steradian for the extrapolated vertical flux of primary alpha particles with energy above (670±100) Mev/nucleon. Some of the alpha particles were seen to interact in copper plates within the cloud chamber. The observations indicate that the collision mean free path is (100±25) g/${\mathrm{cm}}^2$. The problem of counter measurements on components heavier than helium is scrutinized.