Failure of Standard Optical Models to Reproduce Neutron Total Cross Section Differences in the W Isotopes

Abstract

Recently cross section differences among the isotopes ^{182, 184, 186}W have been measured as part of a study of total cross sections in the 5–560 MeV energy range.¹⁾ These measurements show oscillations up to 150 mb between 5 and 100 MeV. Spherical and deformed phenomenological optical potentials with typical radial and isospin dependences show very small oscillations, in disagreement with the data. In a simple Ramsauer model, ^2–4) this discrepancy can be traced to a cancellation between radial and isospin effects. Understanding this problem requires a more detailed model that incorporates a realistic description of the neutron and proton density distributions. This has been done with results of Hartree-Fock-Bogolyubov calculations using the Gogny force, together with a microscopic folding model employing a modification^5,6) of the JLM potential as an effective interaction. This treatment yields a satisfactory interpretation of the observed total cross section differences.

Keywords:

• neutron total cross sections
• Ramsauer model
• spherical optical model
• coupled–channds optical model
• microscopic folding models