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 B${\mathrm{F}}_3$-filled proportional counters. Such coincidences are termed ($s, n$), ($s, 2n$), and so on, according to the number of detected neutrons. The average number, $\overline{\nu }$, 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×${10}^{-4\mathrm{}}$ neutrons ${\mathrm{g}}^{-1\mathrm{}}$ ${\sec }^{-1\mathrm{}}$, 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 $\overline{\nu }=1.3\mathrm{}\pm 0.2$. Combination of this result with previously determined relative multiplicities yields the values $\overline{\nu }=2.2\mathrm{}$ for production in aluminum and $\overline{\nu }=6\mathrm{}$ for production in lead.

• Received 9 September 1953

DOI:https://doi.org/10.1103/PhysRev.93.561