The fore-aft asymmetry and the 90° differential cross section in the ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$(n,${\gamma }_0$) reaction were measured from ${\mathit{E}}_{\mathit{n}}$=8 to 44 MeV. An energy-dependent asymmetry is observed that is interpreted as the result of the isovector giant quadrupole resonance interfering with background E1 amplitudes. The present data agree with previous low-energy data. At higher incident neutron energies, the present data do not agree with the predictions of a direct-semidirect model calculation based on the low-energy data alone. Calculations using the pure resonance model are in agreement with the data.

• Received 7 July 1992

DOI:https://doi.org/10.1103/PhysRevC.46.1880