The total neutron cross section of helium has been determined at energies from 40 kev to 4.9 Mev by comparison of the transmission of neutrons through a helium-filled cylinder with the transmission through an identical empty cylinder. The observed cross section increases smoothly from 0.8 barn at 40 kev to 6.7 barns at 1.15 Mev, and then decreases smoothly to 2.3 barns at 4.9 Mev. No splitting of the peak at 1.15 Mev was observed.

• Received 19 December 1950

DOI:https://doi.org/10.1103/PhysRev.82.378