He6 breakup dynamic polarization potential reexamined

The dynamic polarization potential contribution to the effective interaction between 6He and 208Pb at 27 MeV, due to breakup channels, is recalculated exploiting a recently developed improved model for 6He. The most general features of the long-range attractive and absorptive components remain the same as were found in an earlier study, but the asymptotic magnitudes are reduced by factors of about 2.5 and 4.5, respectively. We draw conclusions from these results, as well as from further calculations at 22 MeV, closer to the Coulomb barrier, and at 32 MeV

Coupling effects in proton scattering from ⁴⁰Ca

Recent studies showed that neutron pickup makes a substantial contribution to the proton optical model potential (OMP) for light, mostly halo, target nuclei. Here, we extend those studies to a more “normal” target nucleus: 40Ca. We present coupled reaction channel (CRC) calculations with the coupling of 30.3 MeV incident protons to deuterons and up to 12 states of 39Ca. The proton elastic scattering S matrix from the CRC calculation is subject to Slj→V(r)+l·s VSO(r) inversion and the bare potential of the CRC calculation is subtracted, directly yielding a local and L-independent representation of the dynamic polarization potential (DPP). This is appropriate for comparison with phenomenological OMPs and local OMPs derived in local density folding models. The real-central part of the DPP is repulsive and cannot be represented as a uniform normalization of the bare potential, changing the rms radius. A series of model calculations reveal the dependence of the DPP on a range of parameters illuminating (i) departures of nucleon potentials of specific nuclei from global properties, (ii) the generation of repulsion, and (iii) the requirements for all-order CRC and deuteron breakup. Light is thrown on the nonlocality of the underlying DPP

Strong pickup-channel coupling effects in proton scattering: the case of p + Be-10

The dynamic polarization potential (DPP) contribution to the effective proton-nucleus interaction, that is due to the coupling of deuteron channels, is evaluated by applying $S_{lj} \to V(r)$ inversion to the elastic channel $S$-matrix from coupled reaction channel calculations of proton elastic scattering. This was done for protons scattering from $^{10}$Be at 12, 13, 14, 15, and 16 MeV; non-orthogonality corrections were included. We find a consistent pattern of a repulsive real and an absorptive imaginary DPP, with the absorption shifted to a larger radius. This is consistent with what has been found for proton scattering from the neutron skin nucleus $^8$He. The DPP is not of a form that can be represented by a renormalization of the bare potential, and has properties suggesting an underlying non-local process. We conclude that deuteron channels cannot be omitted from a full theoretical description of the proton-nucleus interaction (optical potential).Comment: 14 pages, 4 figures, RevTeX4, accepted by Phys Rev

Breakup coupling effects on near-barrier ⁶Li, ⁷Be and ⁸B + ⁵⁸Ni elastic scattering compared

New data for near-barrier 6Li, 7Be and 8B + 58Ni elastic scattering enable a comparison of breakup coupling effects for these loosely-bound projectiles. Coupled Discretised Continuum Channels (CDCC) calculations suggest that the large total reaction cross sections for 8B + 58Ni are dominated by breakup at near-barrier energies, unlike 6Li and 7Be where breakup makes a small contribution. In spite of this, the CDCC calculations show a small coupling influence due to breakup for 8B, in contrast to the situation for 6Li and 7Be. An examination of the S matrices gives a clue to this counter-intuitive behaviour

Observations of an internal resonance in a fjord

Current meter, CTD and tide gauge data collected in a sill fjord in northern British Columbia are considered. Annual changes in stratification are such that the natural internal period of oscillation of the fjord matches that of the semidiurnal tide in both the spring and fall of the year. Evidence of a semidiurnal internal resonance is sought by calculating the ratio of energy and the relative phase of vertical current shear and the barotropic tide. It is possible to show a strong response in the fall coincides with a phase shift of 180° which is the signature of a resonance. Calculations prove the resonant mode to be the first harmonic in both the vertical and horizontal. Results based on springtime data also show a resonant response although it is less clear due to the effects of strong river runoff

Theoretical treatments of fusion processes in collisions of weakly bound nuclei

We review the theoretical methods to evaluate fusion cross sections in collisions of weakly bound nuclei. We piont out that in such collisions the coupling to the breakup channel leads to the appearance of different fusion processes. The extentsion of the coupled-channel method to coupling with the continuum is the most successful treatment for these collisions. However, evaluating separate cross section for each fusion process remains a very hard task.Comment: 8 pages, 3 figures. Invited talk (LFC) at the IX International Conference on Nucleus-Nucleus Collisions, Rio de Janeiro, August 28- September 1, 2006. Nuclear Physics A, in pres

The Onset of Nuclear Structure Effects in Near-Barrier Elastic Scattering of Weakly-Bound Nuclei: 6^6He and 6^6Li Compared

The elastic scattering of the halo nucleus $^6$He from heavy targets at incident energies near the Coulomb barrier displays a marked deviation from the standard Fresnel-type diffraction behavior. This deviation is due to the strong Coulomb dipole breakup coupling produced by the Coulomb field of the heavy target, a specific feature of the nuclear structure of $^6$He. We have performed Continuum Discretized Coupled Channels calculations for the elastic scattering of $^{6}$He and $^6$Li from $^{58}$Ni, $^{120}$Sn, $^{144}$Sm, $^{181}$Ta and $^{208}$Pb targets in order to determine the range of $Z_{\mathrm T}$ where this nuclear-structure specific coupling effect becomes manifest. We find that the strong Coulomb dipole breakup coupling effect is only clearly experimentally distinguishable for targets of $Z_{\mathrm T} \approx 80$.Comment: 10 pages with 3 figure

Remarkable independence of dynamical polarization potentials of the underlying potential

The dynamical polarization potential (DPP) generated by the coupling of specific reaction channels to the elastic channel can be determined by inverting the elastic channel S matrix from a coupled reaction channel (CRC) calculation. The “bare” potential of the CRC calculation is then subtracted from the inverted potential to yield a local representation of the DPP. Here we study the extent to which the DPP calculated in this way depends upon the bare potential. We find that the DPP caused by coupling to pickup channels, for 30.3 MeV protons scattering from 40Ca, turns out to be qualitatively and almost quantitatively unaffected by substantial changes in the bare potential. This puts the properties of DPPs established in this way on a firmer foundation

Pickup coupling contribution to the optical model potential for 30.3 MeV protons and neutrons on⁴⁰Ca

We study the dynamic polarization potentials (DPPs) for 30.3 MeV protons and neutrons scattering from40Ca that are generated by the coupling to deuteron channels. In this way we resolve unexpected differences from the general properties of such DPPs found in similar cases for lighter targets. It turns out that the contribution of particular states to the real part can change considerably with Q value, coming close to changing sign. One consequence is the surprising result presented in Mackintosh and Keeley [Phys. Rev. C 97, 069901(E) (2018)], which is investigated here. The Q-value dependence of the DPPs also contributes to a substantial difference between the optical model potential for protons and neutrons, there being substantially different Q values for 40Ca (n, d) and 40Ca (p, d) pickup reactions. The DPP calculations also enable a study of the dynamical nonlocality (distinct from exchange nonlocality) arising from pickup coupling. The characteristic properties of the DPPs for both protons and neutrons arising from nucleon pickup are also presented for incident nucleons at 25, 35, 40, and 45 MeV. All these properties vary with energy in a consistent way, including a change in the rms radius of the real potential, which, together with the general undularity of the DPP, shows that the pickup contributions cannot be represented by renormalizing a folding model potential