26 research outputs found
Pairing anti-halo effect
We discuss pairing correlations in weakly bound neutron rich nuclei, by using
the coordinate-space Hartree-Fock-Bogolyubov approach which allows to take
properly into account the coupling to particle continuum. We show that the
additional pairing binding energy acts against a development of an infinite rms
radius, even in situations when an l=0 single-particle orbital becomes unbound.Comment: 10 RevTeX pages, 3 EPS figure
Coupling of giant resonances to soft E1 and E2 modes in B-8
The dynamic coupling between giant resonance states and "soft", low-energy
excitation, modes in weakly-bound nuclei is investigated. A coupled-channels
calculation is reported for the reaction 8B + Pb --> p + 7Be + Pb at 83
MeV/nucleon. It is shown that the low-energy response is only marginally
modified by transitions to the isovector giant dipole and isoscalar giant
quadrupole resonances.Comment: 8 pages, 2 figure
Electromagnetic Dissociation as a Tool for Nuclear Structure and Astrophysics
Coulomb dissociation is an especially simple and important reaction
mechanism. Since the perturbation due to the electric field of the (target)
nucleus is exactly known, firm conclusions can be drawn from such measurements.
Electromagnetic matrixelements and astrophysical S-factors for radiative
capture processes can be extracted from experiments. We describe the basic
elements of the theory of nonrelativistic and relativistic electromagnetic
excitation with heavy ions. This is contrasted to electromagnetic excitation
with leptons (electrons), with their small electric charge and the absence of
strong interactions. We discuss various approaches to the study of higher order
electromagnetic effects and how these effects depend on the basic parameters of
the experiment. The dissociation of neutron halo nuclei is studied in a zero
range model using analytical methods. We also review ways how to treat nuclear
interactions, show their characteristics and how to avoid them (as far as
possible). We review the experimental results from a theoretical point of view.
Of special interest for nuclear structure physics is the appearence of low
lying electric dipole strength in neutron rich nuclei. Applications of Coulomb
dissociation to some selected radiative capture reactions relevant for nuclear
astrophysics are discussed. The Coulomb dissociation of 8B is relevant for the
solar neutrino problem. The potential of the method especially for future
investigations of (medium) heavy exotic nuclei for nuclear structure and
astrophysics is explored. We conclude that the Coulomb dissociation mechanism
is theoretically well understood, the potential difficulties are identified and
can be taken care of. Many interesting experiments have been done in this field
and many more are expected in the future.Comment: review article accepted for publication in "Prog. in Part. and Nucl.
Physics", 75 pages, 31 figure
Solar Hydrogen Burning and Neutrinos
We summarize the current status of laboratory measurements of nuclear cross
sections of the pp chain and CN cycle. We discuss the connections between such
measurements, predictions of solar neutrino fluxes, and the conclusion that
solar neutrinos oscillate before reaching earth.Comment: 34 pages, 6 figure
Description of the 17F(p,gamma)18Ne radiative capture reaction in the continuum shell model
The shell model embedded in the continuum is applied to calculate the
astrophysical S-factor and the reaction rate for the radiative proton capture
reaction 17F(p,gamma)18Ne. The dominant contribution to the cross-section at
very low energies is due to M1 transitions J_i^pi = 2^+ --> J_f^pi = 2_1^+
whose magnitude is controlled by a weakly bound 2_2^+ state at the excitation
energy E_x = 3.62 MeV.Comment: 31 pages, latex (uses elsart.cls), 14 figures, submitted to Nuclear
Physics
New reaction rate for 16O( p, γ )17F and its influence on the oxygen isotopic ratios in massive AGB stars
The 16O(p, γ )17F reaction rate is revisited with special emphasis on the stellar temperature range of T=60-100 MK, important for hot bottom burning in asymptotic giant branch (AGB) stars. We evaluate existing cross-section data that were obtained since 1958 and, if appropriate, correct published data for systematic errors that were not noticed previously, including the effects of coincidence summing and updated effective stopping powers. The data are interpreted by using two different models of nuclear reactions, that is, a potential model and R-matrix theory. A new astrophysical S factor and recommended thermonuclear reaction rates are presented. As a result of our work, the 16O(p, γ )17F reaction has now the most precisely known rate involving any target nucleus in the mass A> 12 range, with reaction rate errors of about 7% over the entire temperature region of astrophysical interest (T=0.01-2.5 GK). The impact of the present improved reaction rate with its significantly reduced uncertainties on the hot bottom burning in AGB stars is discussed. In contrast to earlier results we find now that there is not clear evidence to date for any stellar grain origin from massive AGB stars