188 research outputs found
Enlarged deformation region in neutron-rich Zr isotopes by the second intruder orbit
Nuclear deformations and density profiles of neutron-rich even-even Zr
isotopes are investigated using the Skyrme-Hartree-Fock-Bogoliubov method.
Large quadrupole and hexadecapole deformations are predicted along with large
enhancement of the total reaction cross sections at the neutron number
-74. Strong nuclear deformation starting at is induced by the
occupation of the intruder orbit with the asymptotic quantum number
= [550]1/2 originating from the spherical
orbit. The deformation region is further enlarged from to 74 owing to
the occupation of the next intruder orbit with [530]1/2 originating from the
spherical orbit. This characteristic nuclear deformation is
crucially reflected in the systematic behavior of the nuclear radii and the
density profiles near the nuclear surface.Comment: 7 pages, 6 figures, to appear in Phys. Rev. C (Letter
The 21Na(p,gamma)22Mg Reaction and Oxygen-Neon Novae
The 21Na(p,gamma)22Mg reaction is expected to play an important role in the
nucleosynthesis of 22Na in Oxygen-Neon novae. The decay of 22Na leads to the
emission of a characteristic 1.275 MeV gamma-ray line. This report provides the
first direct measurement of the rate of this reaction using a radioactive 21Na
beam, and discusses its astrophysical implications. The energy of the important
state was measured to be E= 205.7 0.5 keV with a resonance
strength meV.Comment: Accepted for publication in Physical Review Letter
Focal Plane Detector System of SHARAQ Spectrometer
International audienceThis report describes the basic performance of the detector system installed in the final momentum-dispersive focal plane of the SHARAQ spectrometer
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
Mapping the deformation in the "island of inversion": Inelastic scattering of Ne 30 and Mg 36 at intermediate energies
The transition strengths of the first-excited 2+ states and deformation lengths of the nuclei Ne30 and Mg36 were determined via Coulomb- and nuclear-force-dominated inelastic scattering at intermediate energies. Beams of these exotic nuclei were produced at the RIKEN Radioactive Isotope Beam Factory and were incident on lead and carbon targets at energies above 200 MeV/u. Absolute excitation cross sections on the lead target yielded reduced transition probabilities of 0.0277(79) and 0.0528(121) e2b2, while the measurements with the carbon target revealed nuclear deformation lengths of ÎŽN=1.98(11) and 1.93(11) fm for Ne30 and Mg36, respectively. Corresponding quadrupole deformation parameters of ÎČ2âŒ0.5 from the two probes were found comparable in magnitude, showing no indication for a reduction in deformation along isotopic and isotonic chains from Mg32 towards the neutron drip-line. Comparisons to shell-model calculations illustrate the importance of neutron excitations across the N=20 shell for Ne30 and suggest that shallow maximums of collectivity may occur around N=22 and 24 along the neon and magnesium isotopic chains, respectivelyA.P. is partly supported by MINECO (Spain) Grant No. FPA2014-57196 and Programme âCentros de Excelencia Severo Ochoaâ SEV-2012-024
The new MRTOF mass spectrograph following the ZeroDegree spectrometer at RIKEN's RIBF facility
A newly assembled multi-reflection time-of-flight mass spectrograph
(MRTOF-MS) at RIKEN's RIBF facility became operational for the first time in
spring 2020; further modifications and performance tests using stable ions were
completed in early 2021. By using a pulsed-drift-tube technique to modify the
ions' kinetic energy in a wide range, we directly characterize the dispersion
function of the system for use in a new procedure for optimizing the voltages
applied to the electrostatic mirrors. Thus far, a mass resolving power of is reached within a total time-of-flight of only
, making the spectrometer capable of studying short-lived
nuclei possessing low-lying isomers. Detailed information about the setup and
measurement procedure is reported, and an alternative in-MRTOF ion selection
scheme to remove molecular contaminants in the absence of a dedicated
deflection device is introduced. The setup underwent an initial on-line
commissioning at the BigRIPS facility at the end of 2020, where more than 70
nuclear masses have been measured. A summary of the commissioning experiments
and results from a test of mass accuracy will be presented.Comment: 13 pages, 11 figure
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