Exploring correlations in exotic nuclei

The difference in neutron total cross section between ⁴⁰Ca and ⁴⁸Ca is sensitive to the n/p asymmetry dependence of the surface imaginary potential in a dispersive optical model analysis, from which spectroscopic information can be extracted. The measured cross sections imply that the strength of neutron correlations changes little as neutron number increases in neutron-rich isotopes. In contrast, for the light-nucleus-induced knockout of the valence neutron in ³⁶Ca, the small experimental knockout cross section (as compared to an eikonal reaction theory) implies a very small spectroscopic factor (and a strong trend in correlations with asymmetry). If this type of knockout analysis is correct, it implies that standard shellmodel calculations miss spectroscopic strength as the Fermi energy nears the continuum. If this is not the case, it may be that there is a problem with the application of the eikonal theory to very deeply bound nucleons at these intermediate energies.