220 research outputs found
Low-Lying Structure of ⁵⁰Ar and the N = 32 Subshell Closure
The low-lying structure of the neutron-rich nucleus 50Ar has been investigated at the Radioactive Isotope Beam Factory using in-beam γ-ray spectroscopy with 9Be (54Ca, 50Ar+γ) X,9Be(55Sc,50Ar+γ)X, and 9Be(56Ti, 50Ar + γ)X multinucleon removal reactions at ∼220 MeV/u. A γ-ray peak at 1178(18) keV is reported and assigned as the transition from the first 2+ state to the 0+ ground state. A weaker, tentative line at 1582(38) keV is suggested as the 4+1→2+1 transition. The experimental results are compared to large-scale shell-model calculations performed in the sdpf model space using the SDPF-MU effective interaction with modifications based on recent experimental data for exotic calcium and potassium isotopes. The modified Hamiltonian provides a satisfactory description of the new experimental results for 50Ar and, more generally, reproduces the energy systematics of low-lying states in neutron-rich Ar isotopes rather well. The shell-model calculations indicate that the N=32 subshell gap in 50Ar is similar in magnitude to those in 52Ca and 54Ti and, notably, predict an N=34 subshell closure in 52Ar that is larger than the one recently reported in 54Ca
Large scale shell model calculations for odd-odd Mn isotopes
Large scale shell model calculations have been carried out for odd-odd
Mn isotopes in two different model spaces. First set of calculations
have been carried out in full shell valence space with two recently
derived shell interactions namely GXPF1A and KB3G treating Ca
as core. The second set of calculations have been performed in
valence space with the interaction treating Ca as core and
imposing a truncation by allowing up to a total of six particle excitations
from the 0f orbital to the upper orbitals for protons and
from the upper orbitals to the 0g orbital for neutron. For
low-lying states in Mn, the KB3G and GXPF1A both predicts good results
and for Mn, KB3G is much better than GXPF1A. For negative parity and
high-spin positive parity states in both isotopes interaction is
required. Experimental data on Mn is sparse and therefore it is not
possible to make any definite conclusions. More experimental data on negative
parity states is needed to ascertain the importance of 0g and higher
orbitals in neutron rich Mn isotopes.Comment: 5 pages, 4 figures, Submitted to Eur. Phys. J.
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
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
Investigating nuclear shell structure in the vicinity of 78 Ni: Low-lying excited states in the neutron-rich isotopes 80, 82 Zn
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 δN=1.98(11) and 1.93(11) fm for Ne30 and Mg36, respectively. Corresponding quadrupole deformation parameters of β2∼0.5 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 “Centros de Excelencia Severo Ochoa” SEV-2012-024
Intermediate-energy Coulomb excitation of 104 Sn: Moderate E2 strength decrease approaching 100 Sn
International audienceThe reduced transition probability B(E2)↑ of the first excited 2 + state in the nucleus 104 Sn was measured via Coulomb excitation in inverse kinematics at intermediate energies. A value of 0.173(28) e 2 b 2 was extracted from the absolute cross section on a Pb target. Feeding contributions in 104 Sn from higher lying states were estimated by a reference measurement of the stable 112 Sn. Corresponding only to a moderate decrease of excitation strength relative to the almost constant values observed in the proton-rich, even-A 106−114 Sn isotopes, present state-of-the-art shell-model predictions, which include proton and neutron excitations across the N = Z = 50 shell closures as well as standard polarization charges, underestimate the experimental findings
Low-Z shore of the “island of inversion” and the reduced neutron magicity toward <font size=-1><sup>28</sup></font>O
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Asymmetry dependence of reduction factors from single-nucleon knockout of <font size=-1><sup>30</sup></font>Ne at ∼ 230 MeV/nucleon
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