218 research outputs found
Linear polarization sensitivity of SeGA detectors
Parity is a key observable in nuclear spectroscopy. Linear polarization
measurements of -rays are a probe to access the parities of energy
levels. Utilizing the segmentation of detectors in the Segmented Germanium
Array (SeGA) at the NSCL and analyzing the positions of interaction therein
allows the detectors to be used as Compton polarimeters. Unlike other segmented
detectors, SeGA detectors are irradiated from the side to utilize the
transversal segmentation for better Doppler corrections. Sensitivity in such an
orientation has previously been untested. A linear polarization sensitivity has been measured in the 350-keV energy range for SeGA detectors
using - correlations from a \nuc{249}{Cf} source.Comment: 7 pages, 9 figure
Magic numbers in exotic nuclei and spin-isospin properties of {\it NN} interaction
The magic numbers in exotic nuclei are discussed, and their novel origin is
shown to be the spin-isospin dependent part of the nucleon-nucleon interaction
in nuclei. The importance and robustness of this mechanism is shown in terms of
meson exchange, G-matrix and QCD theories. In neutron-rich exotic nuclei, magic
numbers such as N = 8, 20, etc. can disappear, while N = 6, 16, etc. arise,
affecting the structure of lightest exotic nuclei to nucleosynthesis of heavy
elements.Comment: 4 pages, 3 figures, revte
Competition between normal and intruder states inside the "Island of Inversion"
The beta decay of the exotic 30Ne (N=20) is reported. For the first time, the
low-energy level structure of the N=19, 30Na (Tz = 4), is obtained from
beta-delayed gamma spectroscopy using fragment-beta-gamma-gamma coincidences.
The level structure clearly displays "inversion", i.e., intruder states with
mainly 2p2h configurations displacing the normal states to higher excitation
energies. The good agreement in excitation energies and the weak and
electromagnetic decay patterns with Monte Carlo Shell Model calculations with
the SDPF-M interaction in the sdpf valence space illustrates the small d3/2 -
f7/2 shell gap. The relative position of the "normal dominant" and "intruder
dominant" excited states provides valuable information to understand better the
N=20 shell gap.Comment: 4 pages, 5 figure
In-beam gamma-ray spectroscopy of 35Mg and 33Na
Excited states in the very neutron-rich nuclei 35Mg and 33Na were populated
in the fragmentation of a 38Si projectile beam on a Be target at 83 MeV/u beam
energy. We report on the first observation of gamma-ray transitions in 35Mg,
the odd-N neighbor of 34Mg and 36Mg, which are known to be part of the "Island
of Inversion" around N = 20. The results are discussed in the framework of
large- scale shell-model calculations. For the A = 3Z nucleus 33Na, a new
gamma-ray transition was observed that is suggested to complete the gamma-ray
cascade 7/2+ --> 5/2+ --> 3/2+ gs connecting three neutron 2p-2h intruder
states that are predicted to form a close-to-ideal K = 3/2 rotational band in
the strong-coupling limit.Comment: Accepted for publication Phys. Rev. C. March 16, 2011: Replaced
figures 3 and 5. We thank Alfredo Poves for pointing out a problem with the
two figure
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
Superdeformation in Asymmetric NZ Nucleus Ar
A rotational band with five -ray transitions ranging from 2 to
12 states was identified in Ar. This band is linked through
transitions from the excited 2, 4 and 6 levels to
the low-lying states; this determines the excitation energy and the spin-parity
of the band. The deduced transition quadrupole moment of 1.45 indicates that the band has a superdeformed shape. The nature of the band
is revealed by cranked Hartree--Fock--Bogoliubov calculations and a
multiparticle--multihole configuration is assigned to the band
An efficient method to evaluate energy variances for extrapolation methods
The energy variance extrapolation method consists in relating the approximate
energies in many-body calculations to the corresponding energy variances and
inferring eigenvalues by extrapolating to zero variance. The method needs a
fast evaluation of the energy variances. For many-body methods that expand the
nuclear wave functions in terms of deformed Slater determinants, the best
available method for the evaluation of energy variances scales with the sixth
power of the number of single-particle states. We propose a new method which
depends on the number of single-particle orbits and the number of particles
rather than the number of single-particle states. We discuss as an example the
case of using the chiral N3LO interaction in a basis consisting up to
184 single-particle states.Comment: 16 pages, 2 figure
Quadrupole Moments of Neutron-Deficient Na
The electric-quadrupole coupling constant of the ground states of the proton
drip line nucleus Na( = 2, = 447.9 ms) and the
neutron-deficient nucleus Na( = 3/2, = 22.49 s)
in a hexagonal ZnO single crystal were precisely measured to be kHz and 939 14 kHz, respectively, using the multi-frequency
-ray detecting nuclear magnetic resonance technique under presence of an
electric-quadrupole interaction. A electric-quadrupole coupling constant of
Na in the ZnO crystal was also measured to be
kHz. The electric-quadrupole moments were extracted as Na) = 10.3
0.8 fm and Na) = 14.0 1.1 fm, using
the electric-coupling constant of Na and the known quadrupole moment of
this nucleus as references. The present results are well explained by
shell-model calculations in the full -shell model space.Comment: Accepted for publication in Physics Letters
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
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