399 research outputs found
Observation of new neutron-rich Mn, Fe, Co, Ni, and Cu isotopes in the vicinity of Ni 78
Neutron-rich nuclei in the vicinity of Ni78 were produced using a U238 beam at the RIKEN Radioactive Isotope Beam Factory. The particle-identification plot for the in-flight fission fragments highlights the first observation of eight new isotopes: Mn73, Fe76, Co77,78, Ni80,81,82, and Cu83. Although the β-decay half-lives of Co77 and Ni80 were recently reported by Xu [Phys. Rev. Lett. 113, 032505 (2014)]PRLTAO0031-900710.1103/PhysRevLett.113.032505 using data from the same experiment, the current work provides the first direct, quantitative evidence for the existence of these isotopes. The experimental production cross sections are reproduced in a satisfactory manner by theoretical predictions. An odd-even staggering of the cross sections was observed, and the effect appears to become more pronounced for the most exotic nuclei that were investigated. The staggering effect was interpreted as an increase of the neutron-evaporation probability for odd-N isotopes, owing to the decrease of the neutron-separation energy, Sn. The predicted cross section for Ni80 is significantly overestimated, which may be related to a weak binding of the neutron pair above the N=50 shell closure
Test of the Conserved Vector Current Hypothesis by beta-ray Angular Distribution Measurement in the Mass-8 System
The beta-ray angular correlations for the spin alignments of 8Li and 8B have
been observed in order to test the conserved vector current (CVC) hypothesis.
The alignment correlation terms were combined with the known beta-alpha-angular
correlation terms to determine all the matrix elements contributing to the
correlation terms. The weak magnetism term, 7.5\pm0.2, deduced from the
beta-ray correlation terms was consistent with the CVC prediction 7.3\pm0.2,
deduced from the analog-gamma-decay measurement based on the CVC hypothesis.
However, there was no consistent CVC prediction for the second-forbidden term
associated with the weak vector current. The experimental value for the
second-forbidden term was 1.0 \pm 0.3, while the CVC prediction was 0.1 \pm 0.4
or 2.1 \pm 0.5.Comment: 31 pages, 12 figures, Accepted for publication in Phys. Rev.
Monopole-Driven Shell Evolution below the Doubly Magic Nucleus Sn132 Explored with the Long-Lived Isomer in Pd126
published_or_final_versio
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
Monopole-driven shell evolution below the doubly magic nucleus Sn 132 explored with the long-lived isomer in Pd 126
A new isomer with a half-life of 23.0(8) ms has been identified at 2406 keV in Pd126 and is proposed to have a spin and parity of 10+ with a maximally aligned configuration comprising two neutron holes in the 1h11/2 orbit. In addition to an internal-decay branch through a hindered electric octupole transition, β decay from the long-lived isomer was observed to populate excited states at high spins in Ag126. The smaller energy difference between the 10+ and 7- isomers in Pd126 than in the heavier N=80 isotones can be interpreted as being ascribed to the monopole shift of the 1h11/2 neutron orbit. The effects of the monopole interaction on the evolution of single-neutron energies below Sn132 are discussed in terms of the central and tensor forces
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
The N = 16 spherical shell closure in 24O
The unbound excited states of the neutron drip-line isotope 24O have been
investigated via the 24O(p,p')23O+n reaction in inverse kinematics at a beam
energy of 62 MeV/nucleon. The decay energy spectrum of 24O* was reconstructed
from the momenta of 23O and the neutron. The spin-parity of the first excited
state, observed at Ex = 4.65 +/- 0.14 MeV, was determined to be Jpi = 2+ from
the angular distribution of the cross section. Higher lying states were also
observed. The quadrupole transition parameter beta2 of the 2+ state was
deduced, for the first time, to be 0.15 +/- 0.04. The relatively high
excitation energy and small beta2 value are indicative of the N = 16 shell
closure in 24O.Comment: to be submitted to Physical Review Letter
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