Optical phase shifts from low-energy neutron cross sections |
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Authors: | WM Macdonald MC Birse |
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Institution: | Department of Physics and Astronomy, University of Maryland, College Park, Maryland 20742, USA |
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Abstract: | The Lorentz-weighted average of the S-matrix introduced by G.E. Brown is used in the Feshbach theory of the generalized optical potential to show that the average many-body S-matrix for elastic scattering is exactly equal to the two-body S-matrix of an optical potential. However, the optical potential S-matrix must be evaluated at the complex energy is the half-width of the lorentzian. The resulting equation for the optical phase shifts (OPS) δc, exp , holds even when the level spacing D forces the use of an averaging half-width I > D which is comparable to the energy E, providing that the OPS are also evaluated at the complex instead of being approximated by their values on the real energy axis at E. An appendix discusses briefly the conditions on a potential necessary for the result obtained by Brown that when Lorentz-weighted averaging is used. |
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Keywords: | Nuclear reactions |
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