Energy dependence of the optical-model potential for fast-neutron scattering from bismuth

Phys. Rev. C 36, 1298 – Published 1 October 1987
R. D. Lawson, P. T. Guenther, and A. B. Smith


Neutron differential-elastic-scattering cross sections of bismuth were measured at ≊0.5 MeV intervals from ≊4.5 to 10.0 MeV. At each incident energy 40 or more differential values were obtained between ≊18° and 160°. These data were combined with lower-energy results previously reported from this laboratory, and others available in the literature, to provide a detailed data base extending from ≊1.5 to 10.0 MeV. This data base was interpreted in terms of the conventional optical-statistical model and also using a model which included the surface-peaked real potential predicted by the dispersion relation. Particular attention was given to the energy dependence of the volume-integral-per-nucleon of the real potential, Jv, to see if there was evidence of the Fermi surface anomaly. In the range 3.010.0 MeV, the present study indicates that dJv/dE is essentially constant, with a relatively large negative value of -6.0 to -9.0 fm3, depending on the model used in the analysis. Below 3.0 MeV, there is some evidence for a decrease in the magnitude of dJv/dE. However, the effect is very small, and it is only when this trend is combined with considerations of the Jv values needed to give correct bound-state energies that evidence for the Fermi surface anomaly emerges. Jv and the geometry of the optical potentials found for Bi209 become equal to those explaining the higher-energy Pb208 data at about 10.0 MeV. Since dJv/dE for the latter is smaller in magnitude than that for Bi209, a change in dJv/dE is clearly indicated near 10.0 MeV.


  • Received 22 May 1987
  • Published in the issue dated October 1987

© 1987 The American Physical Society

Authors & Affiliations

R. D. Lawson, P. T. Guenther, and A. B. Smith

  • Argonne National Laboratory, Argonne, Illinois 60439

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