The scattering of neutrons in ${\mathrm{He}}^4$ has been investigated for neutrons with energies of from 16 to 23.4 Mev with a helium-filled ionization chamber. A pronounced resonance has been found at a neutron energy of 22.15±0.12 Mev. This resonance corresponds to an excitation energy in ${\mathrm{He}}^5$ of 16.72±0.10 Mev which is the same excitation energy as that obtained for the maximum in the $\mathrm{T}(d, n){\mathrm{He}}^4$ cross section. The neutron scattering experiments indicate that the level in ${\mathrm{He}}^5$ has a width of about 100 kev which is much narrower than the ground state of ${\mathrm{He}}^5$. This state in ${\mathrm{He}}^5$ probably has angular momentum and parity of ${\frac{3}{2}}^{+}$ and is made up of two neutrons and a proton in the $S$ shell and one proton and one neutron in the $P$ shell. Such a configuration would explain the large deuteron reduced width of the $\mathrm{T}(d, n){\mathrm{He}}^4$ reaction and the small neutron width.

• Received 24 February 1959

DOI:https://doi.org/10.1103/PhysRev.115.398