Asymmetry dependence of correlations in exotic nuclei.

摘要

This work will discuss two experiments which seek to elucidate the asymmetry dependence of correlations in exotic nuclei. In the first experiment, a digital-signal-processing technique was developed to measure the neutron total cross section of the rare (but stable) isotope 48Ca using a sample that is an order of magnitude smaller than would be required for the conventional technique. The isotopic and energy dependence of neutron total cross sections (e.g. the difference in neutron total cross section between symmetric 40Ca and neutron-rich 48Ca, as a function of energy) is sensitive to the asymmetry dependence of the surface imaginary potential in an optical-model analysis. Exploiting this sensitivity in a Dispersive Optical Model (DOM) allows one to study spectroscopic strength as a function of asymmetry. In the second experiment, the cross sections for hadron-induced single-nucleon knockout from 36Ca were measured. The reduction in spectroscopic strength relative to standard shell-model calculations was obtained for the valence neutron and proton orbitals in 36Ca, by comparison of the experimental cross sections to theoretical cross sections calculated in an eikonal reaction theory. These values were compared to systematics based on previous knockout studies on nuclei with similar N/Z ratios, as well as to predictions for this nucleus based on DOM fits to data including the above-mentioned neutron total cross sections for calcium isotopes. A discrepancy between the trends in spectro-scopic strength deduced from these two methods was confirmed - the trend extracted from knockout experiments is much stronger than that suggested by the present state-of-the-art DOM analysis.