Excitation of a 3 — Collective State by Low-Energy Neutron Scattering

The well-known octupole state at 2.6-MeV excitation in the region of $A=208\mathrm{}$ was excited by inelastic neutron scattering. At 8-MeV incident-neutron energy a distorted-wave Born-approximation analysis of the data yields a value of the deformation ${\beta }_3$ in agreement with the results of other measurements. The reaction mechanism changes rapidly between 6- and 4-MeV incident-neutron energy from dominance of direct interaction to dominance of a compound-nucleus mechanism.