231 research outputs found
Structure of 8B from elastic and inelastic 7Be+p scattering
Motivation: Detailed experimental knowledge of the level structure of light
weakly bound nuclei is necessary to guide the development of new theoretical
approaches that combine nuclear structure with reaction dynamics.
Purpose: The resonant structure of 8B is studied in this work.
Method: Excitation functions for elastic and inelastic 7Be+p scattering were
measured using a 7Be rare isotope beam. Excitation energies ranging between 1.6
and 3.4 MeV were investigated. An R-matrix analysis of the excitation functions
was performed.
Results: New low-lying resonances at 1.9, 2.5, and 3.3 MeV in 8B are reported
with spin-parity assignment 0+, 2+, and 1+, respectively. Comparison to the
Time Dependent Continuum Shell (TDCSM) model and ab initio no-core shell
model/resonating-group method (NCSM/RGM) calculations is performed. This work
is a more detailed analysis of the data first published as a Rapid
Communication. [J.P. Mitchell, et al, Phys. Rev. C 82, 011601(R) (2010)]
Conclusions: Identification of the 0+, 2+, 1+ states that were predicted by
some models at relatively low energy but never observed experimentally is an
important step toward understanding the structure of 8B. Their identification
was aided by having both elastic and inelastic scattering data. Direct
comparison of the cross sections and phase shifts predicted by the TDCSM and ab
initio No Core Shell Model coupled with the resonating group method is of
particular interest and provides a good test for these theoretical approaches.Comment: 15 pages, 19 figures, 3 tables, submitted to PR
Experimental study of excited states of Ni via one-neutron transfer up to the neutron-separation threshold and characteristics of the pygmy dipole resonance states
The degree of collectivity of the Pygmy Dipole Resonance (PDR) is an open
question. Recently, Ries {\it et al.} have suggested the onset of the PDR
beyond based on the observation of a significant strength increase
in the Cr isotopes and proposed that the PDR has its origin in a few-nucleon
effect. Earlier, Inakura {\it et al.} had predicted by performing systematic
calculations using the random-phase approximation (RPA) with the Skyrme
functional SkM* that the strength of the PDR strongly depends on the
position of the Fermi level and that it displays a clear correlation with the
occupation of orbits with orbital angular momenta less than . To further investigate the microscopic structures causing the possible
formation of a PDR beyond the neutron shell closure, we performed a
NiNi experiment at the John D. Fox Superconducting Linear
Accelerator Laboratory of Florida State University. To determine the angular
momentum transfer populating possible states and other excited
states of Ni, angular distributions and associated single-neutron
transfer cross sections were measured with the Super-Enge Split-Pole
Spectrograph. A number of states were observed below the
neutron-separation threshold after being populated through angular
momentum transfers. A comparison to available data for
Ni provides evidence that the strength shifts further down
in energy. The data clearly prove that strength, i.e., the
neutron one-particle-one-hole configuration
plays only a minor role for states below the neutron-separation threshold
in Ni.Comment: 15 pages, 8 figures, accepted for publication in Physical Review
Low-lying states in 8B
Excitation functions of elastic and inelastic 7Be+p scattering were measured
in the energy range between 1.6 and 2.8 MeV in the c.m. An R-matrix analysis of
the excitation functions provides strong evidence for new positive parity
states in 8B. A new 2+ state at an excitation energy of 2.55 MeV was observed
and a new 0+ state at 1.9 MeV is tentatively suggested. The R-matrix and Time
Dependent Continuum Shell Model were used in the analysis of the excitation
functions. The new results are compared to the calculations of contemporary
theoretical models.Comment: 6 pages, 5 figures, accepted as Rapid Communication in Phys. Rev.
-cluster ANCs for nuclear astrophysics
Background. Many important -particle induced reactions for nuclear
astrophysics may only be measured using indirect techniques due to small cross
sections at the energy of interest. One of such indirect technique, is to
determine the Asymptotic Normalization Coefficients (ANC) for near threshold
resonances extracted from sub-Coulomb -transfer reactions. This
approach provides a very valuable tool for studies of astrophysically important
reaction rates since the results are practically model independent. However,
the validity of the method has not been directly verified.
Purpose. The aim of this letter is to verify the technique using the
O(Li,)Ne reaction as a benchmark. The Ne nucleus
has a well known state at excitation energy of 5.79 MeV with a width of
28 eV. Reproducing the known value with this technique is an ideal opportunity
to verify the method.
Method. The 1 state at 5.79 MeV is studied using the -transfer
reaction O(Li,)Ne at sub-Coulomb energies.
Results. The partial width for the state at excitation energy
of 5.79 MeV is extracted and compared with the known value, allowing the
accuracy of the method to be evaluated.
Conclusions. This study demonstrates that extracting the Asymptotic
Normalization Coefficients using sub-Coulomb -transfer reactions is a
powerful tool that can be used to determine the partial width of near
threshold states that may dominate astrophysically important nuclear reaction
rates. \end{description
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