Effects of Angular Momentum in the Decay of Samarium Compound Nuclei

We have measured excitation functions for a series of neutron-emitting compound nucleus reactions leading to the product ${\mathrm{Sm}}^{142}$. By using heavy-ion (HI) beams as bombarding projectiles, it was possible to produce compound nuclei with the same excitation energies but with differing angular momenta. Nine reactions of the type ($\mathrm{HI},xn$), where $x=4\mathrm{} \mathrm{to} 8$, were studied, spanning a region of excitation energies from 40 to 105 MeV. The cross-section maxima are all in the vicinity of 500 mb and occur at energies above threshold corresponding to 4.8-6.3 MeV per emitted neutron. For the same compound nuclei, the effects of increasing angular momentum are to shift the excitation-function peaks toward higher energies and to considerably broaden their width. With increasing number of neutrons emitted, the apparent (extra-polated) threshold energies become increasingly displaced from the true thresholds. Both these displacements and the positions of the excitation function peaks correlate with angular momentum, but it is not possible to distinguish linear relationships from quadratic ones.