The low energy end of the cosmic ray spectrum of alpha-particles

An experiment has been carried out at Saskatoon, Canada, at a nominal geomagnetic latitude of 60.5°N, which shows the form of the low energy end of the cosmic ray alpha particle spectrum independent of the earth's magnetic field. The differential spectrum shows a maximum at about 300 mev per nucleon. The number of particles on the low energy side of the maximum is too great to be accounted for by secondary production, and it is believed that this spectrum represents the differential spectrum of primary alpha particles outside the earth's magnetic field. A re-analysis of previous experiments at a lower geomagnetic latitude, 56°N, in the American continent, gives a spectrum very similar to the one obtained in Saskatoon. As a consequence of this it appears that the cutoff energies experienced by cosmic ray particles over the American continent are probably lower than those predicted by geomagnetic theory.