364 research outputs found
The effect of nuclear deformation on level statistics
We analyze the nearest neighbor spacing distributions of low-lying 2+ levels
of even-even nuclei. We grouped the nuclei into classes defined by the
quadrupole deformation parameter (Beta2). We calculate the nearest neighbor
spacing distributions for each class. Then, we determine the chaoticity
parameter for each class with the help of the Bayesian inference method. We
compare these distributions to a formula that describes the transition to chaos
by varying a tuning parameter. This parameter appears to depend in a
non-trivial way on the nuclear deformation, and takes small values indicating
regularity in strongly deformed nuclei and especially in those having an oblate
deformation.Comment: 10 Pages, 6 figure
Direct reaction measurements with a 132Sn radioactive ion beam
The (d,p) neutron transfer and (d,d) elastic scattering reactions were
measured in inverse kinematics using a radioactive ion beam of 132Sn at 630
MeV. The elastic scattering data were taken in a region where Rutherford
scattering dominated the reaction, and nuclear effects account for less than 8%
of the cross section. The magnitude of the nuclear effects was found to be
independent of the optical potential used, allowing the transfer data to be
normalized in a reliable manner. The neutron-transfer reaction populated a
previously unmeasured state at 1363 keV, which is most likely the
single-particle 3p1/2 state expected above the N=82 shell closure. The data
were analyzed using finite range adiabatic wave calculations and the results
compared with the previous analysis using the distorted wave Born
approximation. Angular distributions for the ground and first excited states
are consistent with the previous tentative spin and parity assignments.
Spectroscopic factors extracted from the differential cross sections are
similar to those found for the one neutron states beyond the benchmark
doubly-magic nucleus 208Pb.Comment: 22 pages, 7 figure
Reactions of a Be-10 beam on proton and deuteron targets
The extraction of detailed nuclear structure information from transfer
reactions requires reliable, well-normalized data as well as optical potentials
and a theoretical framework demonstrated to work well in the relevant mass and
beam energy ranges. It is rare that the theoretical ingredients can be tested
well for exotic nuclei owing to the paucity of data. The halo nucleus Be-11 has
been examined through the 10Be(d,p) reaction in inverse kinematics at
equivalent deuteron energies of 12,15,18, and 21.4 MeV. Elastic scattering of
Be-10 on protons was used to select optical potentials for the analysis of the
transfer data. Additionally, data from the elastic and inelastic scattering of
Be-10 on deuterons was used to fit optical potentials at the four measured
energies. Transfers to the two bound states and the first resonance in Be-11
were analyzed using the Finite Range ADiabatic Wave Approximation (FR-ADWA).
Consistent values of the spectroscopic factor of both the ground and first
excited states were extracted from the four measurements, with average values
of 0.71(5) and 0.62(4) respectively. The calculations for transfer to the first
resonance were found to be sensitive to the size of the energy bin used and
therefore could not be used to extract a spectroscopic factor.Comment: 16 Pages, 10 figure
Universal Predictions for Statistical Nuclear Correlations
We explore the behavior of collective nuclear excitations under a
multi-parameter deformation of the Hamiltonian. The Hamiltonian matrix elements
have the form , with a
parametric correlation of the type . The studies are done in both the regular and chaotic regimes of the
Hamiltonian. Model independent predictions for a wide variety of correlation
functions and distributions which depend on wavefunctions and energies are
found from parametric random matrix theory and are compared to the nuclear
excitations. We find that our universal predictions are observed in the nuclear
states. Being a multi-parameter theory, we consider general paths in parameter
space and find that universality can be effected by the topology of the
parameter space. Specifically, Berry's phase can modify short distance
correlations, breaking certain universal predictions.Comment: Latex file + 12 postscript figure
Nuclear Mass Dependence of Chaotic Dynamics in Ginocchio Model
The chaotic dynamics in nuclear collective motion is studied in the framework
of a schematic shell model which has only monopole and quadrupole degrees of
freedom. The model is shown to reproduce the experimentally observed global
trend toward less chaotic motion in heavier nuclei. The relation between
current approach and the earlier studies with bosonic models is discussed.Comment: 11 Page REVTeX file, 2 postscript figures, uuencode
The magic nature of 132Sn explored through the single-particle states of 133Sn
Atomic nuclei have a shell structure where nuclei with 'magic numbers' of
neutrons and protons are analogous to the noble gases in atomic physics. Only
ten nuclei with the standard magic numbers of both neutrons and protons have so
far been observed. The nuclear shell model is founded on the precept that
neutrons and protons can move as independent particles in orbitals with
discrete quantum numbers, subject to a mean field generated by all the other
nucleons. Knowledge of the properties of single-particle states outside nuclear
shell closures in exotic nuclei is important for a fundamental understanding of
nuclear structure and nucleosynthesis (for example the r-process, which is
responsible for the production of about half of the heavy elements). However,
as a result of their short lifetimes, there is a paucity of knowledge about the
nature of single-particle states outside exotic doubly magic nuclei. Here we
measure the single-particle character of the levels in 133Sn that lie outside
the double shell closure present at the short-lived nucleus 132Sn. We use an
inverse kinematics technique that involves the transfer of a single nucleon to
the nucleus. The purity of the measured single-particle states clearly
illustrates the magic nature of 132Sn.Comment: 19 pages, 5 figures and 4 table
Statistical Fluctuations of Electromagnetic Transition Intensities in pf-Shell Nuclei
We study the fluctuation properties of E2 and M1 transition intensities among
T=0,1 states of A = 60 nuclei in the framework of the interacting shell model,
using a realistic effective interaction for pf-shell nuclei with a Ni56 as a
core. It is found that the B(E2) distributions are well described by the
Gaussian orthogonal ensemble of random matrices (Porter-Thomas distribution)
independently of the isobaric quantum number T_z. However, the statistics of
the B(M1) transitions is sensitive to T_z: T_z=1 nuclei exhibit a Porter-Thomas
distribution, while a significant deviation from the GOE statistics is observed
for self-conjugate nuclei (T_z=0).Comment: 8 pages, latex, 3 figures (ps format
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