507 research outputs found
Shell Model Description of Isotope Shifts in Calcium
Isotope shifts in the nuclear charge radius of even and odd calcium isotopes
are calculated within the nuclear shell model. The model space includes all
configurations of nucleons in the
orbits. The shell model describes well the energies of the intruder states in
Sc and Ca, as well as the energies of the low-lying and states in
the even Ca isotopes. The characteristic features of the isotope shifts, the
parabolic dependence on and the prominent odd-even staggering, are well
reproduced by the model. These features are related to the partial breakdown of
the shell closure caused by promotion, due to the neutron-proton
interaction, of the shell protons into the shell.Comment: 4 pages, 4 figures include
Continuum QRPA response for deformed neutron-rich nuclei
We discuss properties of the quadrupole collective excitation of the deformed
neutron-rich nucleus Mg within the framework of quasi-particle random
phase approximation (QRPA). We first solve the coupled-channels equations to
obtain the single-particle levels, and construct the ground state by treating
the pairing correlations in the BCS approximation. We then solve the QRPA
equation using the response function formalism, by including the continuum
spectra with the box dicscretization method. We show that the collectivity of
the gamma vibration (the lowest mode) is significantly enhanced if
protons and neutrons have different deformations. We also discuss an attempt
towards full continuum QRPA calculations for deformed nuclei.Comment: 8 pages, 2 eps figures. Use espcrc1.sty. A talk given at the
International Conference on Collective Motion in Nuclei Under Extreme
Conditions (COMEX1), June 10 - 13, 2003, Paris, France. To be published in
the proceedings (Nucl. Phys. A
Measurement of excited states in 40Si and evidence for weakening of the N=28 shell gap
Excited states in 40Si have been established by detecting gamma-rays
coincident with inelastic scattering and nucleon removal reactions on a liquid
hydrogen target. The low excitation energy, 986(5) keV, of the 2+[1] state
provides evidence of a weakening in the N=28 shell closure in a neutron-rich
nucleus devoid of deformation-driving proton collectivity.Comment: accepted for publication in PR
Enhanced collectivity in 74Ni
The neutron-rich nucleus 74Ni was studied with inverse-kinematics inelastic
proton scattering using a 74Ni radioactive beam incident on a liquid hydrogen
targetat a center-of-mass energy of 80 MeV. From the measured de-excitation
gamma-rays, the population of the first 2+ state was quantified. The
angle-integrated excitation cross section was determined to be 14(4) mb. A
deformation length of delta = 1.04(16) fm was extracted in comparison with
distorted wave theory, which suggests that the enhancement of collectivity
established for 70Ni continues up to 74Ni. A comparison with results of shell
model and quasi-particle random phase approximation calculations indicates that
the magic character of Z = 28 or N = 50 is weakened in 74Ni
Magnetic dipole probes of the sd and pf shell crossing in the A=36,38 argon isotopes
We have calculated the M1 strength distributions in the A=36,38 argon
isotopes within large-scale shell model studies which consider valence nucleons
in the sd and pf shells. While the M1 strength in 36Ar is well reproduced
within the sd shell, the experimentally observed strong fragmentation of the M1
strength in 38Ar requires configuration mixing between the sd and the pf shells
adding to our understanding of correlations across the N=20 shell gap.Comment: 14 pages, 8 figure
Structure of 55Sc and development of the N=34 subshell closure
The low-lying structure of Sc has been investigated using in-beam
-ray spectroscopy with the Be(Ti,Sc+)
one-proton removal and Be(Sc,Sc+)
inelastic-scattering reactions at the RIKEN Radioactive Isotope Beam Factory.
Transitions with energies of 572(4), 695(5), 1539(10), 1730(20), 1854(27),
2091(19), 2452(26), and 3241(39) keV are reported, and a level scheme has been
constructed using coincidence relationships and -ray
relative intensities. The results are compared to large-scale shell-model
calculations in the - model space, which account for positive-parity
states from proton-hole cross-shell excitations, and to it ab initio
shell-model calculations from the in-medium similarity renormalization group
that includes three-nucleon forces explicitly. The results of proton-removal
reaction theory with the eikonal model approach were adopted to aid
identification of positive-parity states in the level scheme; experimental
counterparts of theoretical and states are
suggested from measured decay patterns. The energy of the first
state, which is sensitive to the neutron shell gap at the Fermi surface, was
determined. The result indicates a rapid weakening of the subshell
closure in -shell nuclei at , even when only a single proton occupies
the orbital
Collectivity evolution in the neutron-rich Pd isotopes towards the N=82 shell closure
The neutron-rich, even-even 122,124,126Pd isotopes has been studied via
in-beam gamma-ray spectroscopy at the RIKEN Radioactive Isotope Beam Factory.
Excited states at 499(9), 590(11), and 686(17) keV were found in the three
isotopes, which we assign to the respective 2+ -> 0+ decays. In addition, a
candidate for the 4+ state at 1164(20) keV was observed in 122Pd. The resulting
Ex(2+) systematics are essentially similar to those of the Xe (Z=54) isotopic
chain and theoretical prediction by IBM-2, suggesting no serious shell
quenching in the Pd isotopes in the vicinity of N=82
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