The multiplication of neutrons by thin spherical shells of various materials surrounding a point source of 14-Mev neutrons has been measured. A special long counter was used whose energy response is independent of neutron energy over a range of energies from about 1 Mev to 14 Mev. The transmission of primary energy neutrons through the shells has been measured with a trans-stilbene detector and values of the inelastic collision cross sections have been derived. The quantity ${\sigma }_{n,2n}+2\mathrm{}{\sigma }_{n,3n}-{\sigma }_c$ is calculated, where ${\sigma }_{n,2n}$ and ${\sigma }_{n,3n}$ are the cross sections for ($n, 2n$) and ($n, 3n$) reactions and ${\sigma }_c$ is the sum of the cross sections of all processes which destroy a neutron. Upper and lower limits are derived for ${\sigma }_{n,2n}$, ${\sigma }_c$, and ${\sigma }_{\mathrm{is}}$ (inelastic scattering) for all materials investigated. For a number of materials specific values for the cross sections are obtained.

• Received 18 October 1954

DOI:https://doi.org/10.1103/PhysRev.97.1205