440 research outputs found
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
Structural evolution in the neutron-rich nuclei 106Zr and 108Zr
The low-lying states in 106Zr and 108Zr have been investigated by means of
{\beta}-{\gamma} and isomer spectroscopy at the RI beam factory, respectively.
A new isomer with a half-life of 620\pm150 ns has been identified in 108Zr. For
the sequence of even-even Zr isotopes, the excitation energies of the first 2+
states reach a minimum at N = 64 and gradually increase as the neutron number
increases up to N = 68, suggesting a deformed sub-shell closure at N = 64. The
deformed ground state of 108Zr indicates that a spherical sub-shell gap
predicted at N = 70 is not large enough to change the ground state of 108Zr to
the spherical shape. The possibility of a tetrahedral shape isomer in 108Zr is
also discussed.Comment: 10 pages, 3 figures, Accepted for publication in Phys. Rev. Let
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
Spectroscopy of 32Ne and the Island of Inversion
We report on the first spectroscopic study of the N=22 nucleus 32Ne at the
newly completed RIKEN Radioactive Ion Beam Factory. A single gamma-ray line
with an energy of 722(9) keV was observed in both inelastic scattering of a 226
MeV/u 32Ne beam on a Carbon target and proton removal from 33Na at 245 MeV/u.
This transition is assigned to the de-excitation of the first J^pi = 2+ state
in 32Ne to the 0+ ground state. Interpreted through comparison with
state-of-the-art shell model calculations, the low excitation energy
demonstrates that the Island of Inversion extends to at least N=22 for the Ne
isotopes.Comment: Accepted for publication in Phys. Rev. Lett. 11 pages, 3 figure
A search for periodic modulations of the solar neutrino flux in Super-Kamiokande-I
A search for periodic modulations of the solar neutrino flux was performed
using the Super-Kamiokande-I data taken from May 31st, 1996 to July 15th, 2001.
The detector's capability of measuring the exact time of events, combined with
a relatively high yield of solar neutrino events, allows a search for
short-time variations in the observed flux. We employed the Lomb test to look
for periodic modulations of the observed solar neutrino flux. The obtained
periodogram is consistent with statistical fluctuation and no significant
periodicity was found
Search for Supernova Relic Neutrinos at Super-Kamiokande
A search for the relic neutrinos from all past core-collapse supernovae was
conducted using 1496 days of data from the Super-Kamiokande detector. This
analysis looked for electron-type anti-neutrinos that had produced a positron
with an energy greater than 18 MeV. In the absence of a signal, 90% C.L. upper
limits on the total flux were set for several theoretical models; these limits
ranged from 20 to 130 nu_e bar cm^-2 s^-1. Additionally, an upper bound of 1.2
nu_e bar cm^-2 s^-1 was set for the supernova relic neutrino flux in the energy
region E_nu > 19.3 MeV.Comment: 4 pages, 2 figures. Submitted to Physical Review Letters. New version
includes corrections to Figure 1. Also, text has been shortened to conform
with the space limitations of PR
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