B. Castel

Nuclear spin response to inelastic proton scattering: Finite geometry and absorption effects

Abstract Recent experiments have clearly demonstrated the ability of inelastic proton scattering to act as a precise probe of the nuclear spin response. Previous calculations based on infinite or semi-infinite matter models differ markedly from experiment in their prediction of longitudinal to transverse response function ratios. The present work indicates that finite geometry and absorption effects are crucial in bringing predictions closer to experiment. The effect of including isobar excitations is also investigated and assessed critically.

The missing charge problem and many-body correlation effects

Abstract The longitudinal sum rule, computed from recent electron scattering experiments is lower than theoretical predictions by about a factor of two. Although the effect of two-particle-two-hole correlations has generally been viewed as the predominant mechanism causing the quenching, its calculation is complex in medium weight and even prohibitive in heavy systems. We present here a simple and efficient method to estimate the effect of the many-particle-many-hole correlation, which borrows from Feshbachs reaction theory, and incorporates effects beyond the usual 2p-2h correlations. The method is introduced in the context of a fully microscopic RPA model and compared with experiment in the case of 40 Ca with particularly encouraging results.

s- and p-wave neutron spectroscopy Xf(ii). Intermediate structure in the 28Si + n reaction: Doorway state calculation☆

Abstract A core-particle calculation developed to describe the low-lying structure of 29Si is extended above neutron threshold energy to yield information on the structure of doorway states indicated by the 29Si + n reaction. The recent experimental evidence for a J = 3 2 − doorway state common to the 28Si + n and the 29Si + γ channels is supported by the calculation which also reproduces correctly the magnitudes of the neutron escape widths and the E1 radiative strengths of the 3 2 − doorway states.

Ikeda's sum rule and charge-exchange reactions on 54Fe☆

Abstract We show that Ikedas sum rule relating (p,n) and (n,p) transition strengths can be used to derive a simple relation linking charge-exchange cross sections in correlated and uncorrelated systems. This relation is then used to show that the recent charge-exchanged results in 54 Fe are completely consistent with RPA correlations and that the role of the Δ isobar in the quenching process is negligible.

Many particle-many hole nuclear correlations and the missing charge problem

Abstract The nuclear longitudinal sum rule, determined from recent electron scattering experiments is lower than theoretical predictions by about a factor of two. Although the effect of two particle-two hole correlations has generally been viewed as the predominant mechanism causing the quenching, its calculation is complex for medium and heavy nuclei. We present here a simple and efficient method to estimate the effect of the many particle-many hole correlation which borrows from Feshbachs reaction theory and incorporates effects beyond the usual 2p-2h correlations. The results are particularly encouraging in comparison with the data in 40 Ca, 48 Ca, and 56 Fe. The calculated sum rule also coincides with experiment at large momentum transfer in all cases studied.

Pion scattering in 208Pb and nuclear surface effects

The authors investigate the apparent anomaly inherent to pi -/ pi + scattering results on giant quadrupole resonances compared to data emanating from other probes. Their study focuses on the radial dependence of the pi + and pi - cross sections based on a continuum RPA calculation for 208Pb. Their conclusion is that, once the highly selective nature of the surface pion absorption process is taken into account, there is indeed consistency between pion and hadron scattering and microscopic theories regarding the isoscalar nature of the GQR.

On the difference between the effective charges used for bound states of29Si and for low-energy neutron radiative capture by28Si

The neutron effective charges used in the analysis of low-energy neutron radiative capture and in nuclear spectroscopy differ by several orders of magnitude. This is illustrated by a quantitative analysis of the28Si(n, γ) reaction; this difference reflects the dominance of external capture.

Structure of doorway states in the40Ca+n reaction

A model including 2p-1h and collective states in41Ca is used to investigate the intermediate structure resonances seen in then+40Ca reaction. With potential well parameters determined by a calculation of the bound states it is found that most of thes-wave strength can be accounted for by the inclusion of one main doorway state component.

d5/2‐single particle strength in 48Ca+n

The neutron total cross section of /sup 48/Ca was measured up to 4 MeV and the data analyzed using an R-matrix code to obtain resonance parameters and potential scattering phase shifts. No s-wave resonances were observed and the small cross section (approx.0.5 b) at low energy requires a real well depth of 48 MeV. Three strong d-wave resonances (amounting to 45% of the single particle limit) were found in the 0.8 to 2.0 MeV energy region. Shell-model-in-the-continuum calculations agree with these observations.

Isospin dependence of the isoscalar giant quadrupole response: Relevance to pion scattering in the Ni isotopes

We study the isospin dependence of the isoscalar giant quadrupole response to pion excitation, with the aim of showing that the apparent anomaly in the π−/π+ analyses is due to the highly selective nature of surface pion absorption. In that context, we present results of continuum RPA calculations which are consistent with recent inelastic pion scattering data on58–64Ni. In general, the calculation predicts a drastic increase in the ratio of neutron to proton transition density in going from56Ni to66Ni, a trend well substantiated by recent LAMPF experiments.