shell model

[paper] Erosion of N=20 shell in ³³Al investigated through the ground-state electric quadrupole moment

Erosion of N=20 shell in ³³Al investigated through the ground-state electric quadrupole moment

K. Shimada et al.

doi: 10.1016/j.physletb.2012.07.030

Electric quadrupole moment Q of the ground state has been measured by means of β-NMR spectroscopy using a spin-polarized beam produced in a projectile fragmentation reaction. The obtained Q moment, |Q_exp(³³Al)|=132(16) emb, shows a significant excess from the prediction of shell model calculations within the sd shell. The result indicates sizable admixing of pf intruder configurations in the ground state, demonstrating that the N=20 shell closure certainly erodes in ³³Al, a nucleus located on the border of the island of inversion. Comparison was made with predictions of the Monte Carlo shell model, and also a particle-vibration coupling model treating the neutron pairing correlations in the ground state of ³³Al. Again, a significant admixture of pf intruder configurations to the ground state was needed in both theoretical approaches to explain the observed large Q.

Aug 14, 2012 by Theo experiment 0

[paper] Structure of the Sr-Zr isotopes near and at the magic N=50 shell from g-factor and lifetime measurements in⁸⁸₄₀Zr and ^84,86,88₃₈Sr

Structure of the Sr-Zr isotopes near and at the magic N=50 shell from g-factor and lifetime measurements in⁸⁸₄₀Zr and ^84,86,88₃₈Sr

G. Kumbartzki et al.

doi: 10.1103/PhysRevC.85.044322

Background: The evolution of and interplay between single-particle and collective excitations in the 40 ⩽N⩽ 50 range for 38Sr and 40Zr isotopes have been studied.

Purpose: Measurement of the g factor of the 2₁⁺ and 4₁⁺ states in radioactive ⁸⁸Zr while simultaneously remeasuring the g(2₁⁺) factors in the Sr isotopes and extention of the measurements to higher energy states in the Sr isotopes. Lifetimes of states in these nuclei are determined.

Methods: The transient field technique in inverse kinematics and line-shape analysis using the Doppler-shift attenuation method are applied. The ⁸⁸Zr nuclei were produced by the transfer of an α particle from the ¹²C nuclei of the target to ⁸⁴Sr nuclei in the beam. The excited states in the stable ⁸⁴Sr isotopes were simultaneously populated via Coulomb excitation by ¹²C in the same target. Coulomb excitation measurements on ^86,88Sr were carried out with the same apparatus.

Results: The resulting g factors and B(E2) values of these nuclei reveal similarities between the two chains of Zr and Sr isotopes. Large-scale shell-model calculations were performed within the p_3/2, f_5/2, p_1/2, g_9/2 orbital space for both protons and neutrons and yielded results in agreement with the experimental data.

Conclusions: In this paper the magnetic moments and lifetimes of several low-lying states in ⁸⁸Zr and ^84,86,88Sr have been measured and compared to large-scale shell-model calculations.

Apr 30, 2012 by Theo experiment g factor 0

[paper] First g-factor measurements of the 2₁⁺ and the 4₁⁺ states of radioactive ¹⁰⁰Pd

First g-factor measurements of the 2₁⁺ and the 4₁⁺ states of radioactive ¹⁰⁰Pd

D.A. Torres et al.

doi: 10.1103/PhysRevC.84.044327

The g factors of the first 2⁺ and 4⁺ states of the radioactive ¹⁰⁰Pd nucleus have been investigated for the first time, using an α-particle transfer reaction from ¹²C to ⁹⁶Ru. The transient magnetic field technique in inverse kinematics was used. The ¹⁰⁰₄₆Pd₅₄ nucleus is a suitable candidate for studying single-particle proton and neutron effects in the nuclear wave functions near the N=Z=50 shell closures. The results are discussed within the frameworks of both large-scale shell-model calculations and collective-model predictions.

Oct 25, 2011 by Theo g factor 0

[paper] Doubly-magic nature of ⁵⁶Ni: Measurement of the ground state nuclear magnetic dipole moment of ⁵⁵Ni

Doubly-magic nature of ⁵⁶Ni: Measurement of the ground state nuclear magnetic dipole moment of ⁵⁵Ni

J.S. Berryman et al.

doi: 10.1103/PhysRevC.79.064305

The nuclear magnetic moment of the ground state of ⁵⁵Ni (I^π=3/2^–, T_1/2=204 ms) has been deduced to be |&mul(⁵⁵Ni)|=(0.976&plusminus;0.026) μ_N using the β-ray detecting nuclear magnetic resonance technique. Results of a shell model calculation in the full fp shell model space with the GXPF1 interaction reproduce the experimental value. Together with the known magnetic moment of the mirror partner ⁵⁵Co, the isoscalar spin expectation value was extracted as <Σσ_z>=0.91&plusminus;0.07. The <Σσ_z> shows a trend similar to that established in the sd shell. The present theoretical interpretations of both &mul(⁵⁵Ni) and <Σσ_z> for the T=1/2, A=55 mirror partners support the softness of the ⁵⁶Ni core.

Jun 5, 2009 by Theo experiment 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] Ground-state electric quadrupole moment of ³¹Al

Ground-state electric quadrupole moment of ³¹Al

D. Nagae et al.

The ground-state electric quadrupole moment of ³¹Al(I^π=5/2⁺,T_1/2=644(25) ms) has been measured by means of β-ray-detected nuclear magnetic resonance spectroscopy using a spin-polarized ³¹Al beam produced in the projectile fragmentation reaction. The obtained Q moment, |Q_exp(³¹Al)|=112(32) e mb, is in agreement with conventional shell model calculations within the sd valence space. Previous results on the magnetic moment also support the validity of the sd model in this isotope, and thus it is concluded that ³¹Al is located outside of the island of inversion

Feb 18, 2009 by Theo experiment 0

[paper] Quadrupole moments of neutron-deficient ^20,21Na

Quadrupole moments of neutron-deficient ^20,21Na

K. Minamisono et al.

doi: 10.1016/j.physletb.2009.01.006

The electric-quadrupole coupling constant of the ground states of the proton drip line nucleus ²⁰Na (I^π=2⁺, T_1/2=447.9 ms) and the neutron-deficient nucleus ²¹Na (I^π=3/2⁺, T_1/2=22.49 s) in a hexagonal ZnO single crystal were precisely measured to be |eqQ/h|=690±12 kHz and 939±14 kHz, respectively, using the multi-frequency β-ray detecting nuclear magnetic resonance technique under presence of an electric-quadrupole interaction. An electric-quadrupole coupling constant of ²⁷Na in the ZnO crystal was also measured to be |eqQ/h|=48.4±3.8 kHz. The electric-quadrupole moments were extracted as |Q(²⁰Na)|=10.3±0.8 efm² and |Q(²¹Na)|=14.0±1.1 efm², using the electric-coupling constant of ²⁷Na and the known quadrupole moment of this nucleus as references. The present results are well explained by shell-model calculations in the full sd-shell model space.

Feb 16, 2009 by Theo experiment 0

[paper] g factor of the exotic N=21 isotope ³⁴Al: probing the N=20 and N=28 shell gaps at the border of the "island of inversion"

g factor of the exotic N=21 isotope ³⁴Al: probing the N=20 and N=28 shell gaps at the border of the "island of inversion"

P. Himpe et al.

doi: 10.1016/j.physletb.2007.11.017

For the first time the g factor of an isotope beyond N=20 near the "island of inversion" has been measured. A ³⁴Al radioactive beam was produced in a one-neutron pickup reaction on a ³⁶S primary beam at 77.5 MeV/u, providing a large spin-polarization for application of the β-Nuclear Magnetic Resonance (β-NMR) method. The measured g factor of ³⁴Al, |g|=0.539(2), combined with results from earlier β-decay studies, allows to firmly assign a ground state spin/parity 4⁻. Comparison to large scale shell model calculations reveals that a dominant amount of intruder components is needed in the ³⁴Al wave function to account for the observed large magnetic moment μ=(+)2.156(16)μ_N. This reveals Z=13 to be a true "transition number" between the normal Z=14 Si isotopes and the abnormal Z=12 Mg isotopes. The sensitivity of this odd–odd ground state dipole moment to the N=20, as well as the N=28 gap, reveals that both are significantly reduced, despite Z=13 being outside the conventional island of inversion.

Jan 10, 2008 by Theo experiment g factor 0

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