142 research outputs found
Structure of 10N in 9C+p resonance scattering
The structure of exotic nucleus 10N was studied using 9C+p resonance
scattering. Two L=0 resonances were found to be the lowest states in 10N. The
ground state of 10N is unbound with respect to proton decay by 2.2(2) or 1.9(2)
MeV depending on the 2- or 1- spin-parity assignment, and the first excited
state is unbound by 2.8(2) MeV.Comment: 6 pages, 4 figures, 1 table, submitted to Phys. Lett.
alpha-cluster structure of 18Ne
In this work we study alpha-clustering in 18Ne and compare it with what is
known about clustering in the mirror nucleus 18O. The excitation function of
18Ne was measured in inverse kinematics from the resonant elastic scattering
reaction of 14O on 4He in the excitation energy range from 8 to 17 MeV, using
the active target TexAT. The analysis was performed using a multi-channel
R-matrix approach. Detailed spectroscopic information is obtained from the
R-matrix analysis: excitation energy of the states, spin and parity as well as
partial alpha and total widths. This information is compared with theoretical
models and previous data. Clustering structures appear to be robust and mostly
isospin symmetric. A good correspondence was found between the levels in 18O
and 18Ne. We carried out an extensive shell model analysis of the experimental
data. This comparison suggests that strongly clustered states remain organized
in relation to the corresponding reaction channel identified by the number of
nodes in the relative alpha plus core wave function. The agreement between
theory and experiment is very good and especially useful when it comes to
understanding the clustering strength distribution. The comparison of the
experimental data with theory shows that certain states, especially at high
excitation energies, are significantly more clustered than predicted. This
indicates that the structure of these states is collective and is aligned
towards the corresponding alpha reaction channel
Decay properties of resonances and their impact on -process nucleosynthesis
The astrophysical -process is one of the two main processes forming
elements heavier than iron. A key outstanding uncertainty surrounding
-process nucleosynthesis is the neutron flux generated by the
reaction during the He-core
and C-shell burning phases of massive stars. This reaction, as well as the
competing reaction, is
not well constrained in the important temperature regime from --~GK, owing to uncertainties in the nuclear properties of resonances
lying within the Gamow window. To address these uncertainties, we have
performed a new measurement of the reaction in inverse kinematics, detecting the outgoing
deuterons and recoils in coincidence. We have
established a new decay branching ratio of for the key
MeV resonance in , which results in a new
strength for this resonance of eV when combined with
the well-established strength of this resonance. We have
also determined new upper limits on the partial widths of
neutron-unbound resonances at , , and
MeV. Monte-Carlo calculations of the stellar and rates, which incorporate these results, indicate
that both rates are substantially lower than previously thought in the
temperature range from --~GK.Comment: 17 pages, 4 figures, accepted for publication in Phys. Lett.
Probing the quadrupole transition strength of C15 via deuteron inelastic scattering
Deuteron elastic scattering from C and inelastic scattering reactions to the first excited state of C were studied using a radioactive beam of C in inverse kinematics. The scattered deuterons were measured using HELIOS. The elastic scattering differential cross sections were analyzed using the optical model. A matter deformation length δd = 1.04(11) fm has been extracted from the differential cross sections of inelastic scattering to the first excited state. The ratio of neutron and proton matrix elements Mn/Mp = 3.6(4) has been determined from this quadrupole transition. Neutron effective charges and core-polarization parameters of C were determined and discussed. Results from ab initio no-core configuration interaction calculations were also compared with the experimental observations. This result supports a moderate core decoupling effect of the valence neutron in C similarly to its isotone O, in line with the interpretation of other neutron-rich carbon isotopes.Deuteron elastic scattering from 15C and inelastic scattering reactions to the first excited state of 15C were studied using a radioactive beam of 15C in inverse kinematics. The scattered deuterons were measured using HELIOS. The elastic scattering differential cross sections were analyzed using the optical model. A matter deformation length δd = 1.04(11) fm has been extracted from the differential cross sections of inelastic scattering to the first excited state. The ratio of neutron and proton matrix elements Mn/Mp = 3.6(4) has been determined from this quadrupole transition. Neutron effective charges and core-polarization parameters of 15C were determined and discussed. Results from ab-initio no-core configuration interaction calculations were also compared with the experimental observations. This result supports a moderate core decoupling effect of the valence neutron in 15C similarly to its isotone 17O, in line with the interpretation of other neutron-rich carbon isotopes
Study of the Mg waiting point relevant for x-ray burst nucleosynthesis via the Mg(,)Al reaction
The Mg(,)Al reaction rate has been identified as a
major source of uncertainty for understanding the nucleosynthesis flow in
Type-I x-ray bursts (XRBs). We report a direct measurement of the energy- and
angle-integrated cross sections of this reaction in a 3.3-6.9 MeV
center-of-mass energy range using the MUlti-Sampling Ionization Chamber
(MUSIC). The new Mg(,)Al reaction rate is a factor of
4 higher than the previous direct measurement of this reaction within
temperatures relevant for XRBs, resulting in the Mg waiting point of
x-ray burst nucleosynthesis flow to be significantly bypassed via the
() reactionComment: 6 pages, 3 figures, 1 tabl
Study of the Isomeric State in N Using the N(,He) Reaction
The isomeric state of N was studied using the
N(,He)~proton-removal reactions at \mbox{11.8~MeV/} in
inverse kinematics. The N beam, of which 24% was in the isomeric state,
was produced using the ATLAS in-fight facility and delivered to the HELIOS
spectrometer, which was used to analyze the He ions from the
(,He) reactions. The simultaneous measurement of reactions on both the
ground and isomeric states, reduced the systematic uncertainties from the
experiment and in the analysis. A direct and reliable comparison of the
relative spectroscopic factors was made based on a Distorted-Wave Born
Approximation approach. The experimental results suggest that the isomeric
state of N is an excited neutron-halo state. The results can be
understood through calculations using a Woods-Saxon potential model, which
captures the effects of weak-binding.Comment: 8 pages, 7 figur
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