theory

[paper] Quadrupole moments of collective structures up to spin ∼65ℏ in ¹⁵⁷Er and ¹⁵⁸Er: A challenge for understanding triaxiality in nuclei

Quadrupole moments of collective structures up to spin ∼65ℏ in ¹⁵⁷Er and ¹⁵⁸Er: A challenge for understanding triaxiality in nuclei

X. Wang et al.

doi: 10.1016/j.physletb.2011.07.007

The transition quadrupole moments, Q_t, of four weakly populated collective bands up to spin ∼65ℏ in ^157,158Er have been measured to be ∼11 eb demonstrating that these sequences are associated with large deformations. However, the data are inconsistent with calculated values from cranked Nilsson–Strutinsky calculations that predict the lowest energy triaxial shape to be associated with rotation about the short principal axis. The data appear to favor either a stable triaxial shape rotating about the intermediate axis or, alternatively, a triaxial shape with larger deformation rotating about the short axis. These new results challenge the present understanding of triaxiality in nuclei.

Jul 13, 2011 by Theo experiment g factor theory 0

[paper] g factors of nuclear low-lying states: A covariant description

g factors of nuclear low-lying states: A covariant description

JiangMing Yao et al.

doi: 10.1007/s11433-010-4214-8

The g factors and spectroscopic quadrupole moments of low-lying excited states 2₁⁺, …, 8₁⁺ in ₂₄Mg are studied in a covariant density functional theory. The wave functions are constructed by configuration mixing of axially deformed mean-field states projected on good angular momentum. The mean-field states are obtained from the constraint relativistic point-coupling model plus BCS calculations using the PC-F1 parametrization for the particle-hole channel and a density-independent delta-force for the particle-particle channel. The available experimental g factor and spectroscopic quadrupole moment of 2₁/⁺ state are reproduced quite well. The angular momentum dependence of g factors and spectroscopic quadrupole moments, as well as the effects of pairing correlations are investigated

Dec 6, 2010 by Theo theory 0

[paper] Shape coexistence near the N=38 shell gap: Magnetic moment of the 981.6 keV J^π=8⁺ level in ⁷²As

Shape coexistence near the N=38 shell gap: Magnetic moment of the 981.6 keV J^π=8⁺ level in ⁷²As

D. Pantelică et al.

doi: 10.1103/PhysRevC.82.044313

We report on the first determination of the magnetic moment of the 981.1 keV, J^π=8⁺ level in ⁷²As, a nucleus that belongs to the A≈70 mass region dominated by rapidly changing deformations and shapes. The 8⁺ level is the bandhead of a collective sequence of positive parity levels coexisting with low-spin and medium-spin spherical shell-model states. The magnetic moment was measured by the time-integral perturbed angular distributions method to be μ=-(4.272±0.280)μ_N. This value is in disagreement with the presumed [π(1g_9/2),ν(1g_9/2)] configuration and points to a more complex configuration involving two neutrons in the 1g_9/2 orbital.

Oct 20, 2010 by Theo experiment g factor theory 0

[paper] Magnetic moment of ¹⁰⁴Ag^m and the hyperfine magnetic field of Ag in Fe using nuclear magnetic resonance on oriented nuclei

Magnetic moment of ¹⁰⁴Ag^m and the hyperfine magnetic field of Ag in Fe using nuclear magnetic resonance on oriented nuclei

V.V. Golovko et al.

doi: 10.1103/PhysRevC.81.054323

Nuclear magnetic resonance (NMR/ON) measurements with β- and γ-ray detection have been performed on oriented ¹⁰⁴Ag^g,m nuclei with the NICOLE ³He-⁴He dilution refrigerator setup at ISOLDE/CERN. For ¹⁰⁴Ag^g (I^π=5⁺) the γ-NMR/ON resonance signal was found at ν=266.70(5) MHz. Combining this result with the known magnetic moment for this isotope, the magnetic hyperfine field of Ag impurities in an Fe host at low temperature (<1 K) is found to be |B_hf(AgFe)|=44.709(35) T. A detailed analysis of other relevant data available in the literature yields three more values for this hyperfine field. Averaging all four values yields a new and precise value for the hyperfine field of Ag in Fe; that is, |B_hf(AgFe)|=44.692(30) T. For ¹⁰⁴Ag^m (I^π=2⁺), the anisotropy of the β particles provided the NMR/ON resonance signal at ν=627.7(4) MHz. Using the new value for the hyperfine field of Ag in Fe, this frequency corresponds to the magnetic moment μ(^104mAg)=+3.691(3) μ_N, which is significantly more precise than previous results. The magnetic moments of the even-A ^102-110Ag isotopes are discussed in view of the competition between the (πg_9/2)^7/2+-3(νd_5/2νg_7/2)^5/2+ and the (πg_9/2)^9/2+-3(νd_5/2νg_7/2)^5/2+ configurations. The magnetic moments of the ground and isomeric states of ¹⁰⁴Ag can be explained by an almost complete mixing of these two configurations.

May 28, 2010 by Theo experiment g factor theory 0

[paper] g factor of the ⁴⁴Cl ground state: Probing the reduced Z=16 and N=28 gaps

g factor of the ⁴⁴Cl ground state: Probing the reduced Z=16 and N=28 gaps

M. De Rydt et al.

doi: 10.1103/PhysRevC.81.034308

The g factor of the ⁴⁴Cl ground state is measured at the LISE fragment separator at the Grand Acclérateur National d’Ions Lourds (GANIL) using the β nuclear magnetic resonance technique, resulting in g(⁴⁴Cl)=(-)0.2749(2). An analysis of the g factor value and of the theoretical level scheme in the shell-model framework reveals the presence of odd-proton s_1/2 configurations and neutron excitation across the N=28 shell gap in the ground state of ⁴⁴Cl. In addition, the measured g factor strongly supports a 2^– spin assignment for the ⁴⁴Cl ground state.

Mar 19, 2010 by Theo experiment g factor theory 0

[paper] Magnetic moments of ³³Mg in the time-odd relativistic mean field approach

Magnetic moments of ³³Mg in the time-odd relativistic mean field approach

Jian Li et al.

doi: 10.1007/s11433-009-0194-y

The configuration-fixed deformation constrained relativistic mean field approach with time-odd component has been applied to investigate the ground state properties of ³³Mg with effective interaction PK1. The ground state of ³³Mg has been found to be prolate deformed, β₂=0.23, with the odd neutron in 1/2[330] orbital and the energy −251.85 MeV which is close to the data −252.06 MeV. The magnetic moment −0.9134 µ_N is obtained with the effective electromagnetic current which well reproduces the data −0.7456 µ_N self-consistently without introducing any parameter. The energy splittings of time reversal conjugate states, the neutron current, the energy contribution from the nuclear magnetic potential, and the effect of core polarization are discussed in detail.

Oct 10, 2009 by Theo theory 0

[paper] Up to N³LO heavy-baryon chiral perturbation theory calculation for the M1 properties of three-nucleon systems

Up to N³LO heavy-baryon chiral perturbation theory calculation for the M1 properties of three-nucleon systems

Y.-H. Song et al.

10.1103/PhysRevC.79.064002

M1 properties, comprising magnetic moments and radiative capture of thermal neutron observables, are studied in two- and three-nucleon systems. We use meson exchange current derived up to N³LO using heavy baryon chiral perturbation theory à la Weinberg. Calculations have been performed for several qualitatively different realistic nuclear Hamiltonians, which permits us to analyze model dependence of our results. Our results are found to be strongly correlated with the effective range parameters such as binding energies and the scattering lengths. Taking into account such correlations, the results are in good agreement with the experimental data with small model dependence.

Jun 22, 2009 by Theo theory 0

[paper] Nuclear structure of the even-even argon isotopes with a focus on magnetic moments

Nuclear structure of the even-even argon isotopes with a focus on magnetic moments

S.J.Q. Robinson et al.

10.1103/PhysRevC.79.054322″

We study the role of configuration mixing in the heavier even-even isotopes of argon. We begin by limiting the configurations of the even-even Ar isotopes to (d_3/2²)_&pi (f_7/2ⁿ)_ν. There, due to the particular location in this shell-model space of ⁴⁰Ar and ⁴⁴Ar, we find that the spectra, B(E2)’s, and magnetic moments of these two nuclei are identical. Any deviation from this equality is direct evidence of configuration mixing. In a larger shell-model space there are significant differences between these two nuclei, with ⁴⁴Ar being more collective. We also consider other even-even isotopes of argon and study how their nuclear structure effects evolve with N. We compare in the full 0ℏ ω space (sd)_π (fp)_ν the results of calculations with the WBT interaction and with the newer SDPF, denoted SDPF-U, interaction.

May 18, 2009 by Theo theory 0

[paper] Charge radii and electromagnetic moments of Li and Be isotopes from the ab initio no-core shell model

Charge radii and electromagnetic moments of Li and Be isotopes from the ab initio no-core shell model

C. Forssén et al.

Recently, charge radii and ground-state electromagnetic moments of Li and Be isotopes were measured precisely. We have performed large-scale ab initio no-core shell model calculations for these isotopes using high-precision nucleon-nucleon potentials. The isotopic trends of our computed charge radii and quadrupole and magnetic-dipole moments are in good agreement with experimental results with the exception of the ¹¹Li charge radius. The magnetic moments are in particular well described, whereas the absolute magnitudes of the quadrupole moments are about 10% too small. The small magnitude of the ⁶Li quadrupole moment is reproduced, and with the CD-Bonn NN potential, also its correct sign.

Feb 25, 2009 by Theo theory 0

[paper] Quantum Monte Carlo calculations of magnetic moments and M1 transitions in A≤7 nuclei including meson-exchange currents

Quantum Monte Carlo calculations of magnetic moments and M1 transitions in A≤7 nuclei including meson-exchange currents

L.E. Marcucci et al.

doi: 10.1103/PhysRevC.78.065501

Green’s function Monte Carlo calculations of magnetic moments and M1 transitions including two-body meson-exchange current (MEC) contributions are reported for A≤7 nuclei. The realistic Argonne v₁₈ two-nucleon and Illinois-2 three-nucleon potentials are used to generate the nuclear wave functions. The two-body meson-exchange operators are constructed to satisfy the continuity equation with the Argonne v₁₈ potential. The MEC contributions increase the A=3,7 isovector magnetic moments by 16% and the A=6,7 M1 transition rates by 17–34%, bringing them into very good agreement with the experimental data.

Dec 10, 2008 by Theo g factor theory 0

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