Emission of Alpha Particles from Nuclei Having Large Angular Momenta

The statistical theory of nuclear de-excitation predicts α-particle energy spectra having important features that were missed in earlier, less complete calculations. To a good approximation, the α spectrum is composed of three qualitatively different subspectra. For Dy156* compound nuclei formed by Ce¹⁴⁰+O¹⁶ at 90 MeV (lab), these subspectra have their respective maxima at 17, 12, and 7.5 MeV. The 7.5-MeV subspectrum should be resolvable into a group of sharp lines. The crucial roles of the lowest excited state at every angular momentum (the yrast levels), and of the competition with neutron and with dipole and quadrupole γ-ray emission, are stressed. Simple formulas are derived for estimating the energies at the maxima of the two lowest-energy subspectra. Since the α-particle subspectra are predictions of the most widely used version of the statistical model of nuclear de-excitation, a failure to observe them would be important. If they are observed, the experimental data should provide information about several nuclear properties heretofore inaccessible.