22 research outputs found
alpha-nucleus potentials for the neutron-deficient p nuclei
alpha-nucleus potentials are one important ingredient for the understanding
of the nucleosynthesis of heavy neutron-deficient p nuclei in the astrophysical
gamma-process where these p nuclei are produced by a series of (gamma,n),
(gamma,p), and (gamma,alpha) reactions. I present an improved alpha-nucleus
potential at the astrophysically relevant sub-Coulomb energies which is derived
from the analysis of alpha decay data and from a previously established
systematic behavior of double-folding potentials.Comment: 6 pages, 3 figures, accepted for publication in Phys. Rev.
The 106Cd(α, α)106Cd elastic scattering in a wide energy range for γ process studies
Date of Acceptance: 15/04/2015Alpha elastic scattering angular distributions of the 106Cd(α, α)106Cd reaction were measured at three energies around the Coulomb barrier to provide a sensitive test for the α + nucleus optical potential parameter sets. Furthermore, the new high precision angular distributions, together with the data available from the literature were used to study the energy dependence of the locally optimized α + nucleus optical potential in a wide energy region ranging from ELab=27.0MeV down to 16.1 MeV.The potentials under study are a basic prerequisite for the prediction of α-induced reaction cross sections and thus, for the calculation of stellar reaction rates used for the astrophysical γ process. Therefore, statistical model predictions using as input the optical potentials discussed in the present work are compared to the available 106Cd + alpha cross section data.Peer reviewe
Long range effects on the optical model of 6He around the Coulomb barrier
We present an optical model (OM) analysis of the elastic scattering data of
the reactions 6He+27Al and 6He+208Pb at incident energies around the Coulomb
barrier. The bare part of the optical potential is constructed microscopically
by means of a double folding procedure, using the Sao Paulo prescription
without any renormalization. This bare interaction is supplemented with a
Coulomb dipole polarization (CDP) potential, which takes into account the
effect of the dipole Coulomb interaction. For this CDP potential, we use an
analytical formula derived from the semiclassical theory of Coulomb excitation.
The rest of the optical potential is parametrized in terms of Woods-Saxon
shapes. In the 6He+208Pb case, the analysis confirms the presence of long range
components, in agreement with previous works. Four-body Continuum-Discretized
Coupled-Channels calculations have been performed in order to better understand
the features of the optical potentials found in the OM analysis. This study
searches to elucidate some aspects of the optical potential of weakly bound
systems, such as the dispersion relation and the long range (attractive and
absorptive) mechanisms.Comment: Accepted in Nucl. Phys. A; 26 pages, 8 figures, 6 tables
Photon-induced Nucleosynthesis: Current Problems and Experimental Approaches
Photon-induced reactions play a key role in the nucleosynthesis of rare
neutron-deficient p-nuclei. The paper focuses on (gamma,alpha), (gamma,p), and
(gamma,n) reactions which define the corresponding p-process path. The relation
between stellar reaction rates and laboratory cross sections is analyzed for
photon-induced reactions and their inverse capture reactions to evaluate
various experimental approaches. An improved version S_C(E) of the
astrophysical S-factor is suggested which is based on the Coulomb wave
functions. S_C(E) avoids the apparent energy dependence which is otherwise
obtained for capture reactions on heavy nuclei. It is found that a special type
of synchrotron radiation available at SPring-8 that mimics stellar blackbody
radiation at billions of Kelvin is a promising tool for future experiments. By
using the blackbody synchrotron radiation, sufficient event rates for
(gamma,alpha) and (gamma,p) reactions in the p-process path can be expected.
These experiments will provide data to improve the nuclear parameters involved
in the statistical model and thus reduce the uncertainties of nucleosynthesis
calculations.Comment: 13 pages, 6 figures, EPJA, accepte
Improved +He potentials by inversion, the tensor force and validity of the double folding model
Improved potential solutions are presented for the inverse scattering problem
for +He data. The input for the inversions includes both the data of
recent phase shift analyses and phase shifts from RGM coupled-channel
calculations based on the NN Minnesota force. The combined calculations provide
a more reliable estimate of the odd-even splitting of the potentials than
previously found, suggesting a rather moderate role for this splitting in
deuteron-nucleus scattering generally. The approximate parity-independence of
the deuteron optical potentials is shown to arise from the nontrivial
interference between antisymmetrization and channel coupling to the deuteron
breakup channels. A further comparison of the empirical potentials established
here and the double folding potential derived from the M3Y effective NN force
(with the appropriate normalisation factor) reveals strong similarities. This
result supports the application of the double folding model, combined with a
small Majorana component, to the description even of such a loosely bound
projectile as the deuteron. In turn, support is given for the application of
iterative-perturbative inversion in combination with the double folding model
to study fine details of the nucleus-nucleus potential. A -He tensor
potential is also derived to reproduce correctly the negative Li quadrupole
moment and the D-state asymptotic constant.Comment: 22 pages, 12 figures, in Revte
Cross section predictions for hydrostatic and explosive burning
We review different models used for reactions involved in nuclear
astrophysics. The reaction rate is defined for resonant as well as for
non-resonant processes. For low-density nuclei, we describe the DWBA method,
the potential model, the R-matrix method, and microscopic cluster models. The
statistical model is developed for high-level densities. Details of
calculations in the low- and high-density regimes are illustrated with new
results concerning transfer reactions and level densities.Comment: 25 pages, 3 figures, invited article to appear in Nucl. Phys.
Study of the Zr()Y reaction at 22 MeV
The () reaction on Zr has been studied in a high
resolution experiment at an incident proton energy of 22 MeV.
The cross section and asymmetry angular distributions for
transitions to 36 levels of Y with an excitation energy up to 3
MeV have been measured.
DWBA analyses of experimental angular distributions, using either Woods-Saxon
or Double Folded potentials for the exit channel, have
been done, allowing either the confirmation of previous spin and parity values
or the assignment of new spin and parity to a large
number of states. The structure of low lying states of Y
has been studied in the framework of the shell model, using the OXBASH code.
With the interaction PMM90 reasonable agreement is obtained for part of the
negative parity spectrum