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Classification of Energy Levels in
Phys. Rev. 85, 643 – Published 15 February, 1952
DOI: https://doi.org/10.1103/PhysRev.85.643
Abstract
The differential cross section for the elastic scattering of protons by has been measured by Mooring, Koester, Goldberg, Saxon, and Kaufmann in the range of bombarding energies between 0.4 Mev and 3.95 Mev. In the present work, the energy dependence of this cross section is interpreted in terms of the combination of Coulomb and nuclear potential scattering with resonant scattering. This resonant scattering arises from the excitation of energy levels of the compound nucleus . The general trend of the observed cross section between 0.4 Mev and 3.4 Mev, including the three broadest resonances, is well fitted theoretically.
A method is developed to calculate the effects of imperfect energy resolution on the shapes of resonances, and the results are used to rule out certain assignments.
The excited states corresponding to the three broadest resonances have been classified as follows: 3.11 Mev, ; 3.88 Mev, ; 5.34 Mev, . These energies are the dissociation energy, which is 2.32 Mev, plus the resonant energy in the center-of-mass system. A twofold ambiguity remains in the angular momentum values assigned to the narrow resonances because the experimental resolution was not sufficient to determine their true maximum cross sections. The assignments are as follows: 3.75 Mev, ; 3.91 Mev, ; 4.25 Mev, ; 4.63 Mev, ; 5.83 Mev, . The last assignment is somewhat doubtful because the phase shifts due to higher, unobserved resonances are not known.
The odd parity levels have reduced widths between 10 percent and 30 percent of the value corresponding to single particle excitation, while the even parity levels have reduced widths only a few tenths of one percent of this value. An explanation of the level structure is offered in terms of a nuclear shell model. The spin-orbit splitting of the 3.11 Mev and 3.88 Mev states is small compared with doublet splitting observed in closed-shell plus-one nuclei.
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