165 research outputs found
Open issues in extracting nuclear structure information from the breakup of exotic nuclei
The open issues in the development of models for the breakup of exotic nuclei
and the link with the extraction of structure information from experimental
data are reviewed. The question of the improvement of the description of exotic
nuclei within reaction models is approached in the perspective of previous
analyses of the sensitivity of these models to that description. Future
developments of reaction models are suggested, such as the inclusion of various
channels within one model. The search for new reaction observables that can
emphasise more details of exotic nuclear structure is also proposed.Comment: 18 pages, 4 figures, submitted as a contribution to the Secial Issue
on "Nuclear reaction theory" of the Journal of Physics G, guest edited by
R.C. Johnson and F.M. Nune
Reconciling Coulomb breakup and neutron radiative capture
The Coulomb-breakup method to extract the cross section for neutron radiative
capture at astrophysical energies is analyzed in detail. In particular, its
sensitivity to the description of the neutron-core continuum is ascertained. We
consider the case of 14C(n, )15C for which both the radiative capture
at low energy and the Coulomb breakup of 15C into 14C+n on Pb at 68 MeV/nucleon
have been measured with accuracy. We confirm the direct proportionality of the
cross section for both reactions to the square of the asymptotic normalization
constant of 15C observed by Summers and Nunes [Phys. Rev. C 78, 011601 (2008)],
but we also show that the 14C-n continuum plays a significant role in the
calculations. Fortunately, the method proposed by Summers and Nunes can be
improved to absorb that continuum dependence. We show that a more precise
radiative-capture cross section can be extracted selecting the breakup data at
forward angles and low 14C-n relative energies.Comment: Erratum added in the Appendix
From the Coulomb breakup of halo nuclei to neutron radiative capture
Coulomb breakup is used to infer radiative-capture cross sections at
astrophysical energies. We test theoretically the accuracy of this indirect
technique in the particular case of 15C, for which both the Coulomb breakup to
^{14}C+n and the radiative capture 14C(n,{\gamma})15C have been measured. We
analyse the dependance of Coulomb-breakup calculations on the projectile
description in both its initial bound state and its continuum. Our calculations
depend not only on the Asymptotic Normalisation Coefficient (ANC) of the 15C
ground state, but also on the 14C-n continuum. This questions the method
proposed by Summers and Nunes [Phys. Rev. C 78, 011601 (2008), ibid. 78, 069908
(2008)], which assumes that an ANC can be directly extracted from the
comparison of calculations to breakup data. Fortunately, the sensitivity to the
continuum description can be absorbed in a normalisation constant obtained by a
simple {\chi}2 fit of our calculations to the measurements. By restricting this
fit to low 14C-n energy in the continuum, we can achieve a better agreement
between the radiative-capture cross sections inferred from the Coulomb-breakup
method and the exact ones. This result revives the Coulomb-breakup technique to
infer neutron radiative-capture capture to loosely-bound states, which would be
very useful for r- and s-process modelling in explosive stellar environments.Comment: 8 pages, 7 figures, contribution to the proceedings of the 54th
International Winter Meeting on Nuclear Physics (25-29 January 2016, Bormio,
Italy
Analysis of a low-energy correction to the eikonal approximation
Extensions of the eikonal approximation to low energy (20MeV/nucleon
typically) are studied. The relation between the dynamical eikonal
approximation (DEA) and the continuum-discretized coupled-channels method with
the eikonal approximation (E-CDCC) is discussed. When Coulomb interaction is
artificially turned off, DEA and E-CDCC are shown to give the same breakup
cross section, within 3% error, of C on Pb at 20MeV/nucleon.
When the Coulomb interaction is included, the difference is appreciable and
none of these models agrees with full CDCC calculations. An empirical
correction significantly reduces this difference. In addition, E-CDCC has a
convergence problem. By including a quantum-mechanical correction to E-CDCC for
lower partial waves between C and Pb, this problem is resolved
and the result perfectly reproduces full CDCC calculations at a lower
computational cost.Comment: 8 pages, 7 figure
Extending the Eikonal Approximation to Low Energy
E-CDCC and DEA, two eikonal-based reaction models are compared to CDCC at low
energy (e.g. 20AMeV) to study their behaviour in the regime at which the
eikonal approximation is supposed to fail. We confirm that these models lack
the Coulomb deflection of the projectile by the target. We show that a hybrid
model, built on the CDCC framework at low angular momenta and the eikonal
approximation at larger angular momenta gives a perfect agreement with CDCC. An
empirical shift in impact parameter can also be used reliably to simulate this
missing Coulomb deflection.Comment: Contribution to the proceedings of the Conference on "Advances in
Radioactive Isotope Science" (ARIS2014). 6 pages, 4 figure
Study of clustering structures through breakup reactions
Models for the description of breakup reactions used to study the structure
of exotic cluster structures like halos are reviewed. The sensitivity of these
models to the projectile description is presented. Calculations are sensitive
to the projectile ground state mostly through its asymptotic normalisation
coefficient (ANC). They also probe the continuum of the projectile. This
enables studying not only the bound states of the projectile but also its
continuum, both resonant and non-resonant. This opens the possibility to study
correlations between both halo neutrons in two-neutron halo nuclei.Comment: Contribution to the proceedings of the 3rd international Workshop on
"State of the Art in Nuclear Cluster Physics" (SotANCP, 26-30 May 2014,
Yolohama, Japan). 7 pages, 6 figure
Recent advances in the description of reactions involving exotic nuclei
In this contribution to the proceedings of the International Nuclear Physics
Conference 2019, I review recent developments made in reaction models used to
analyse data measured at radioactive-ion beam facilities to study exotic
nuclear structures. I focus in particular on reactions like elastic scattering
and breakup, which are used to study halo nuclei. Although these peculiar
nuclei challenge usual nuclear-structure models, some can now be computed ab
initio. This brief review illustrates the progresses made in nuclear-reaction
theory in the last few years to improve the description of the projectile
within reaction models. I dedicate this contribution to the memory of Mahir
Hussein, who has significantly contributed to this field and who passed away in
May this year.Comment: Contribution to the proceedings of the International Nuclear Physics
Conference 2019. 8 pages, 8 figure
Sensitivity of one-neutron knockout of halo nuclei to their nuclear structure
Halo nuclei are located far from stability and exhibit a very peculiar
structure. Due to their very short lifetime, they are often studied through
reactions. Breakup reactions are of particular interest since their cross
sections are large for these loosely-bound nuclei. Inclusive measurements of
breakup--also called knockout reactions--have even higher statistics. In this
proceeding, we study which nuclear-structure information can be inferred from
the parallel-momentum distribution of the core of one-neutron halo nuclei after
the knockout of its halo neutron. In particular, we analyse the influence of
the ground-state wavefunction, the presence of excited states within the
halo-nucleus spectrum and resonances in the core-neutron continuum. Our
analysis shows that such observables are sensitive to the tail of the
ground-state wavefunction. The presence of excited state decreases the breakup
strength, and this flux is transferred to the inelastic-scattering channel.
This indicates a conservation of the flux within each partial wave. We also
show that the parallel-momentum distributions are insensitive to the existence
of resonances within the continuum, they can thus be ignored in practice. This
independence on the continuum argues that the parallel-momentum distributions
are ideal observables to extract very precisely the ANCs of halo nuclei.Comment: 6 pages, 3 figures, INPC 2019 proceeding
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