K. Takase

Ground-state electric quadrupole moment of 31 Al

levels are lowered [3, 4] and theirB(E2) values are enhanced [5] sizably in these isotopes,and the possibility of deformation has been proposed.Theoretical analyses [6] discussed the importance of 2p-2h excitations from the sd shell to the upper pf shell,and concluded it plausible that an inversion of ampli-tudes between the sd normal and pf intruder configura-tions would lead to deformation of the ground states.The region of nuclei where such a phenomenon occurs iscalled the island of inversion. In elucidating the under-lying mechanism for the inversion, the measurements ofthe electromagnetic moments have played an importantrole. For example in a series of neutron-rich Na isotopes,it has been found that, once entering the island of in-version, the ground-state magnetic dipole moment µ andelectric quadrupole moment Q [7, 8] show clear devia-tions from the conventional shell-model predictions [9],indicating that µ and Q are sensitive to changes in thenuclear configuration [10]. Also in the recent study of Mgisotopes, anomalous ground-state properties have beenrevealed through the µ-moment measurements [11, 12].In the present work, the ground-state Q moment of

Nuclear moments of neutron-rich 32Al

The magnetic moment and electric quadrupole moment of 32Al (Z = 13,N = 19) have been measured. We performed β-NMR spectroscopy with spin-polarized 32Al nuclei produced via the projectile fragmentation reaction. Both the moments are well reproduced by full sd-shell model calculations using the USD effective interaction. The result has provided clear evidence that 32Al is located out of the island of inversion.

Production of spin-polarized radioactive ion beams via projectile fragmentation reaction

Spin‐polarized radioactive ion beams are produced in the projectile fragmentation reaction induced by intermediate‐energy heavy ion beams. The degree of spin polarization shows characteristic dependence on the outgoing momentum of the projectile fragment in the magnitude around 1∼10%. The qualitative behavior is well described by the kinematical model of the fragmentation process. Recently, we have successfully produced spin‐polarized beams of aluminum isotopes in the mass A∼30 region via the fragmentation of 95 MeV/u 40Ar projectiles. The magnetic moments of 30Al and 32Al and the electric quadrupole moments of 31Al and 32Al have been measured using the β‐NMR technique with the polarized RI beams of the Al isotopes.

Measurement of nuclear moments at RIKEN

Based on the technique of fragment‐induced spin polarization combined with the β‐NMR method, we have recently carried out experiments at RIKEN to measure nuclear moments of neutron‐rich aluminum isotopes. In the measurements, the nuclear magnetic‐dipole moments of 30, 32Al and the electric‐quadrupole moments of 31,32Al have been determined. The obtained magnetic moments, as well as the other known magnetic moments of aluminum isotopes, agree well with shell model calculations with the USD interaction. The obtained quadrupole moments are smaller than those of 27, 28Al, suggesting spherical shapes of 31, 32Al. These results seem to suggest that 31Al and 32Al are located outside the island of inversion. In near future, studies on nuclear moments will be extended further in the RIKEN RIBF project, in which medium‐ and heavy‐mass regions come within our scope by using superconducting fragment separator BigRIPS. Also, an upgrade program for the existing fragment separator RIPS is in progress. In the RIBF projec...

Measurement of Electric Quadrupole Moments for 31Al Using Spin Polarized RI Beams

The electromagnetic moment is a sensitive probe to investigate microscopic structure. In order to measure the electromagnetic moment, β‐NMR and β‐NQR methods are employed taking advantage of the fragment spin polarization produced by the fragmentation reaction. The measurement of the electric quadrupole moment for ground‐state 31Al has been been carried out by β‐NQR method. Spin‐polarized 31Al nuclei were obtained from the fragmentation of 40Ar projectiles, and were implanted in α‐Al2O3 stopper. The electric quadrupole moment was deduced from the measured quadrupole coupling constant. The obtained value is |Q(31Al)| = 104(9) e⋅mb.

Production of Polarized Radioactive Beams via The Inverse-kinematics Reactions and Their Applications

The development of techniques to produce low‐energy spin‐polarized radioactive nucleon beams (RNBs) is reported. It employs the inverse‐kinematics reactions of law energy heavy‐ion beams for the RNB production with in‐flight separator. Some plans of research are discussed that apply these well‐focused, conveniently energetic spin‐polarized RNB to nuclear structure physics and material science.

Nuclear‐moment measurements at RIKEN and perspectives in RIBF

Based on the technique of fragment‐induced spin polarization combined with the β‐NMR method, a series of experiments has been carried out at RIKEN for the nuclear‐moment measurement of light unstable nuclei. The measurement will be extended further in the RIKEN RIBF project, where radioactive‐isotope beams in the medium‐ and heavy‐mass regions will be produced at higher energies and with higher intensities compared with the RARF facility. Measurements of the isomeric‐state nuclear moments of unstable nuclei will be started with BigRIPS by utilizing fragment‐induced spin‐orientation phenomena. Also, an upgrade program of the existing fragment separator RIPS is proposed in the phase‐II program of RIBF. Then, intense beams will be delivered to RIPS at E ∼ 115 A MeV. This energy region is useful, not only because spin orientation is produced in the PF reaction but also they can be implanted into sample materials with limited thickness.

Electric Quadrupole Moments of Neutron Rich Al Isotope

The electric quadrupole moment Q for the ground state of neutron‐rich 31,32Al has been measured using β‐NMR method applied to spin‐polarized projectile fragments. The obtained quadrupole moments are smaller than those of 27,28Al, which suggests spherical shapes of 31,32Al.

Structure of unstable nuclei from nuclear moments and β decays

The structure of neutron-rich nuclei around the N = 20 magic number is studied through the measurements of static electromagnetic moments. Recent data on the magnetic dipole moments and electric quadrupole moments for neutron-rich Al isotopes are discussed to clarify whether the emergence of a strong deformation reported for Z = 10?12 nuclei in this region might happen also in these Z = 13 nuclei. Possibility to study the nuclear structure via the ? transition matrix elements is also discussed.