Search

The current diversity and inconsistency among published quadrupole moments calls for a thorough evaluation of the available data. In this work, a review of the ground-state Q-moments of the oxygen to calcium isotopes is presented, resulting in a revised database of 43 quadrupole moments. For every π (sd) isotope chain, the quadrupole moments are expressed relative to one reference isotope. This common reference rules out the existing arbitrariness and provides a reliable basis for future measurements and theoretical studies. In addition, the evaluated quadrupole-moment values are compared to shell-model calculations, obtained with different effective interactions in the sd and sdpf model spaces and using the standard effective charges e p = 1.3 e and e n = 0.5 e . The discrepancy between theory and experiment, observed for particular isotopes and isotope chains, calls for further fundamental research.

Electric quadrupole moment Q of the Al 33 ground state has been measured by means of β-NMR spectroscopy using a spin-polarized Al 33 beam produced in a projectile fragmentation reaction. The obtained Q moment, | Q exp ( 33 Al ) | = 132 ( 16 ) e mb , 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 Al 33 , 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 Al 33 . Again, a significant admixture of pf intruder configurations to the Al 33 ground state was needed in both theoretical approaches to explain the observed large Q.

A new β -NMR / β -NQR setup is developed to study nuclear magnetic dipole moments and electric quadrupole moments at the LISE fragment separator at GANIL. Two key elements make the new design very powerful: the homogeneous magnet and the strong radio-frequency amplifier. The combination of both makes it possible to examine a broad spectrum of magnetic dipole and electric quadrupole moments. Several factors have an influence on the detection efficiency and on the sensitivity of the setup to observe a resonant change in the β -asymmetry : the thickness and the tilting angle of the implantation crystal, the material in the vacuum chamber, the applied magnetic field and the Q β -value of the decaying nuclei. A detailed study of these effects is made using a dedicated GEANT4 Monte Carlo simulation code.

The electric quadrupole coupling constant of the 31 Al ground state is measured to be ν Q = | e Q V z z h | = 2196 ( 21 ) kHz using two different β -NMR (Nuclear Magnetic Resonance) techniques. For the first time, a direct comparison is made between the continuous rf technique and the adiabatic fast passage method. The obtained coupling constants of both methods are in excellent agreement with each other and a precise value for the quadrupole moment of 31 Al has been deduced: | Q ( Al 31 ) | = 134.0 ( 16 ) mb . Comparison of this value with large-scale shell-model calculations in the sd and sdpf valence spaces suggests that the 31 Al ground state is dominated by normal sd-shell configurations with a possible small contribution of intruder states. The obtained value for | Q ( Al 31 ) | and a compilation of measured quadrupole moments of odd- Z even- N isotopes in comparison with shell-model calculations shows that the proton effective charge e p = 1.1 e provides a much better description of the nuclear properties in the sd-shell than the adopted value e p = 1.3 e .

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.