Neutron Production by Cosmic Rays

An experimental study has been made of the production of neutrons in the nuclear interactions of cosmic rays. An apparatus selected events in which a nuclear interaction occurred in or near a liquid scintillation counter, with the production not only of ionizing particles but also of neutrons of a few Mev energy which were slowed to thermal energy in a paraffin moderator and detected by BF₃-filled proportional counters. Such coincidences are termed ($s, n$), ($s, 2n$), and so on, according to the number of detected neutrons. The average number, ν, of neutrons produced per disintegration was calculated from the observed relative numbers of ($s, n$) and ($s, 2n$) coincidences.These data were obtained at Climax, Colorado, at an altitude of 11 200 ft. Analysis shows that events of the type selected in this experiment account for the production of 3×{}10^-4 neutrons g^-1 sec^-1, a figure which is close to the total neutron-production rate in carbon as previously measured at the same location. In these events, it is concluded that ν=1.3±0.2. Combination of this result with previously determined relative multiplicities yields the values ν=2.2 for production in aluminum and ν=6 for production in lead.