155 research outputs found
Effects of nuclear molecular configurations on the astrophysical S-factor for O + O
The impact of nuclear molecular configurations on the astrophysical S-factor
for O + O is investigated within the realistic two-center shell
model based on Woods-Saxon potentials. These molecular effects refer to the
formation of a neck between the interacting nuclei and the radial dependent
collective mass parameter. It is demonstrated that the former is crucial to
explain the current experimental data with high accuracy and without any free
parameter, whilst in addition the latter predicts a pronounced maximum in the
S-factor. In contrast to very recent results by Jiang et al., the S-factor does
not decline towards extremely low values as energy decreases.Comment: In press in Physics Letters
A simple analytic model for astrophysical S-factors
We propose a physically transparent analytic model of astrophysical S-factors
as a function of a center-of-mass energy E of colliding nuclei (below and above
the Coulomb barrier) for non-resonant fusion reactions. For any given reaction,
the S(E)-model contains four parameters [two of which approximate the barrier
potential, U(r)]. They are easily interpolated along many reactions involving
isotopes of the same elements; they give accurate practical expressions for
S(E) with only several input parameters for many reactions. The model
reproduces the suppression of S(E) at low energies (of astrophysical
importance) due to the shape of the low-r wing of U(r). The model can be used
to reconstruct U(r) from computed or measured S(E). For illustration, we
parameterize our recent calculations of S(E) (using the Sao Paulo potential and
the barrier penetration formalism) for 946 reactions involving stable and
unstable isotopes of C, O, Ne, and Mg (with 9 parameters for all reactions
involving many isotopes of the same elements, e.g., C+O). In addition, we
analyze astrophysically important 12C+12C reaction, compare theoretical models
with experimental data, and discuss the problem of interpolating reliably known
S(E) values to low energies (E <= 2-3 MeV).Comment: 13 pages, 5 figures, Phys. Rev. C, accepte
Suppression of complete fusion due to breakup in the reactions B + Bi
Above-barrier cross sections of -active heavy reaction products, as
well as fission, were measured for the reactions of B with
Bi. Detailed analysis showed that the heavy products include components
from incomplete fusion as well as complete fusion (CF), but fission originates
almost exclusively from CF. Compared with fusion calculations without breakup,
the CF cross sections are suppressed by 15% for B and 7% for B. A
consistent and systematic variation of the suppression of CF for reactions of
the weakly bound nuclei Li, Be, B on targets of
Pb and Bi is found as a function of the breakup threshold
energy
Relating breakup and incomplete fusion of weakly-bound nuclei through a classical trajectory model with stochastic breakup
A classical dynamical model that treats break-up stochastically is presented
for low energy reactions of weakly-bound nuclei. The three-dimensional model
allows a consistent calculation of breakup, incomplete and complete fusion
cross sections. The model is assessed by comparing the breakup observables with
CDCC quantum mechanical predictions, which are found to be in reasonable
agreement. Through the model, it is demonstrated that the breakup probability
of the projectile as a function of its distance from the target is of primary
importance for understanding complete and incomplete fusion at energies near
the Coulomb barrier.Comment: Accepted in Physical Review Letter
Measurement of 1323 and 1487 keV resonances in 15N({\alpha}, {\gamma})19F with the recoil separator ERNA
The origin of fluorine is a widely debated issue. Nevertheless, the
^{15}N({\alpha},{\gamma})^{19}F reaction is a common feature among the various
production channels so far proposed. Its reaction rate at relevant temperatures
is determined by a number of narrow resonances together with the DC component
and the tails of the two broad resonances at E_{c.m.} = 1323 and 1487 keV.
Measurement through the direct detection of the 19F recoil ions with the
European Recoil separator for Nuclear Astrophysics (ERNA) were performed. The
reaction was initiated by a 15N beam impinging onto a 4He windowless gas
target. The observed yield of the resonances at Ec.m. = 1323 and 1487 keV is
used to determine their widths in the {\alpha} and {\gamma} channels. We show
that a direct measurement of the cross section of the
^{15}N({\alpha},{\gamma})^{19}F reaction can be successfully obtained with the
Recoil Separator ERNA, and the widths {\Gamma}_{\gamma} and {\Gamma}_{\alpha}
of the two broad resonances have been determined. While a fair agreement is
found with earlier determination of the widths of the 1487 keV resonance, a
significant difference is found for the 1323 keV resonance {\Gamma}_{\alpha} .
The revision of the widths of the two more relevant broad resonances in the
15N({\alpha},{\gamma})19F reaction presented in this work is the first step
toward a more firm determination of the reaction rate. At present, the residual
uncertainty at the temperatures of the ^{19}F stellar nucleosynthesis is
dominated by the uncertainties affecting the Direct Capture component and the
364 keV narrow resonance, both so far investigated only through indirect
experiments.Comment: 8 pages, 11 figures. Accepted for publication in PR
Systematical study of the optical potential for systems like A+ 58Ni from sub-barrier data analyses
Elastic scattering differential cross sections were measured for the 28Si158Ni system at sub-barrier energies.
The corresponding nuclear potential was compared with earlier results of systems like A158Ni. The present
data also allowed the determination of the 28Si nuclear density through an unfolding method. The experimentally
extracted 28Si density values are compared with those previously obtained for the 4,6He, 12C, 16,18O
nuclei. We present a critical discussion of the absolute precision obtained for the density parameters extracted
from the data analyses
Elastic scattering, inelastic excitation, and 1 n pick-up transfer cross sections for 10 B + 120 Sn at energies near the Coulomb barrier
The
10
B
+
120
Sn
reaction has been systematically studied at laboratory energies around the Coulomb barrier:
E
LAB
=
31.5
, 33.5, 35.0, and 37.5 MeV. Cross sections for the elastic scattering and some reaction processes have been measured: excitation to the
1
+
state of
10
B
; excitation to the
2
+
and
3
−
states of
120
Sn
; and the one-neutron pick-up transfer
120
Sn
(
10
B
,
11
B
)
119
Sn
. Coupled reaction channel (CRC) calculations have been performed in the context of the double-folding São Paulo potential. The theoretical calculations result in a good overall description of the experimental angular distributions. The effect on the theoretical elastic-scattering angular distributions of couplings to the inelastic and transfer states (through the CRC calculations) and to the continuum states (through continuum-discretized coupled-channels calculations) has been investigated.Instituto Nacional de Ciência e Tecnologia–Física Nuclear e Aplicações (INCT-FNA) 464898/2014-5Ministerio de Economía y Competitividad de España y el Fondo Europeo de Desarrollo Regional (FEDER) FIS2014-51941-P,Junta de Andalucía. FQM-160Programa de investigación e innovación de la Unión Europea Horizonte 2020. 65400
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