b-NMR

[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, |Qexp(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.

[paper] Hyperfine field and hyperfine anomalies of copper impurities in iron

Hyperfine field and hyperfine anomalies of copper impurities in iron

V. V. Golovko et al.

doi: 10.1103/PhysRevC.84.014323

A new value for the hyperfine magnetic field of copper impurities in iron is obtained by combining resonance frequencies from experiments involving β-NMR on oriented nuclei on 59Cu, 69Cu, and 71Cu with magnetic moment values from collinear laser spectroscopy measurements on these isotopes. The resulting value, i.e., Bhf(CuFe) = -21.794(10) T, is in agreement with the value adopted until now but is an order of magnitude more precise. It is consistent with predictions from ab initio calculations. Comparing the hyperfine field values obtained for the individual isotopes, the hyperfine anomalies in Fe were determined to be 59Δ69=0.15(9)% and 71Δ69=0.07(11)%.

[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 s1/2 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.

[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 (Iπ=3/2, T1/2=204 ms) has been deduced to be |&mul(55Ni)|=(0.976&plusminus;0.026) μN 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 <Σσz>=0.91&plusminus;0.07. The <Σσz> shows a trend similar to that established in the sd shell. The present theoretical interpretations of both &mul(55Ni) and <Σσz> for the T=1/2, A=55 mirror partners support the softness of the 56Ni core.

[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(Iπ=5/2+,T1/2=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, |Qexp(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

[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)μN. 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.

[paper] Magnetic moments of 3013Al17 and 3213Al19

Magnetic moments of 3013Al17 and 3213Al19

H. Ueno et al.

doi: 10.1016/j.physletb.2005.04.037

Ground-state magnetic moments of 30Al and 32Al were measured
with the β-NMR method using radioactive-isotope beams spin-polarized in the projectile-fragmentation
reaction. Polarization of sizes |P|=0.5–1% were obtained in spite of the large numbers of nucleons
that are removed from the projectile 40Ar, providing a promising prospect that
substantial polarizations are obtained even in fragment nuclei that are far removed from the projectile nucleus.
The obtained μ moments, |μexp(30Al)|=3.010(7) μN
and |μexp(32Al)|=1.959(9) μN, are in agreement with
shell model calculations within the sd valence space, although a reduction in the energy-gap between
the sd and pf states is predicted for 32Al in recent theoretical studies.