island of inversion

[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] 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] 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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