Apparent Absence of Low-Energy Primary Cosmic Radiation

Abstract

THE form of the energy spectrum of primary cosmic rays is still uncertain at the low-energy end. The work of Carmichael and Dymond1 and of Bowen, Millikan and Neher2 suggested that there was a lower limit at about 2,000 MeV., but this has not been confirmed by Pomerantz3, who has come to the conclusion that the spectrum continues down to low energies. The matter is of importance owing to its cosmological implications. If the existence of a cut-off in the spectrum be established, some mechanism must be found either for removing the slower particles as they travel through space, or for their initial acceleration with a sharp low-energy limit. The suggestion of Janossy that a solar magnetic dipole field might be responsible is not now supported by the astronomical evidence.