D. Nagae

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.

Beta Neutrino Correlation and T‐Violation Experiment in Nuclear Beta Decay

Precision measurement of nuclear beta decay correlations at newly constructing RIKEN‐RIBF and KEK‐TRIAC is planned. Measurements of beta neutrino correlation and T‐violating electron transverse polarization using spin polarized RI beams are aimed to be performed using slow radioactive nuclei.

Lamb-shift Polarized Ion Source at UTTAC

The Lamb-shift polarized ion source (PIS) was installed as one of the ion sources for the 12UD Pelletron tandem accelerator at the University of Tsukuba Tandem Accelerator Complex (UTTAC) in 1976. The PIS makes it possible to produce highly polarized negative proton and deuteron beams. However, the Great East Japan Earthquake on 11 March 2011 seriously damaged not only the accelerator but also the PIS. Following the disaster, it was decided that the PIS should be reconstructed and used as the ion source for the newly designed 6 MV tandem accelerator. Main components including the duoplasmatron chamber and spin filter were reused, while other components including the accelerator tubes and some beam ducts were newly produced. After the reconstruction of the PIS, we attempted to generate polarized beams and measure the polarization. Recently, we attempted to produce unstable nuclei with the polarized proton beam for measurements of nuclear moments of unstable nuclei.

Development Of Secondary Electron Time Detector For Ion Beams

A time detector is under development for the mass measurement with the Rare-RI (radioactive iso- tope) Ring at the RI beam factory (RIBF) in RIKEN. To perform successful mass measurement, a time detector requires a small energy loss of the ion beams, a good time resolution, and a suf- ficient detection efficiency. To satisfy these requirements, our time detector utilizes isochronous transport of the secondary electrons emitted from a thin foil. The isochronous transport of the electrons from the foil to the micro-channel plate (MCP) detector is provided by the crossed electromagnetic field. To improve the detection efficiency, the transport time of the electrons is reduced by a factor of two using a strong magnetic field. An experiment to test the performance of the time detector was carried out with heavy ion beams. The time resolution was σ < 100 ps with a maximum detection efficiency of 99% for heavy ion beams. The details of the detector are presented in this contribution.

Performance of a Resonant Schottky Pick-up in the Commissioning of Rare-RI Ring

Rare-RI Ring was constructed at RIKEN RIBF for precise isochronous mass spectrometry of unstable nuclei. In June 2015, we performed the first commissioning of the ring using 78Kr beam with the energy of 168 MeV/nucleon. We successfully carried out the individual injection which is one of the characteristics of the ring, and also we succeeded in the storage of 78Kr ions for a few seconds. We evaluated the performance of the resonant Schottky pick-up which was installed in the Rare-RI Ring. The purpose of the resonant Schottky pick-up is a monitor for tuning of the isochronous field in the ring. The resonant Schottky pick-up detected single 78Kr ions, where the frequency resolution was 1.29×10−6 (FWHM). The resolution is in the same order of the required isochronicity. The sensitivity and resolution of the resonant Schottky pick-up are sufficient for the tuning of isochronous optics.

Developments of Time-of-Flight Detectors for Rare-RI Ring

Construction of the Rare-RI Ring to measure masses of short-lived rare-RI with a relative precision of 10 -6 is in progress at RIKEN [1, 2]. The mass is determined by measuring a time-of-flight (TOF). For determination of nuclear masses with high precision, TOF detectors should be as thin as possible with a good timing resolution ( < 100 ps). We are developing two types of TOF detectors for the Rare-RI Ring, one is to be used for timing measurements before injection to the ring, to provide a start signal for TOF inside the ring, and the other is to be used for direct circulation measurements inside the ring. For the former type of detector, we develop specially configured “T-shaped” scintillation counters with a thin plastic scintillator (100 m) to be accommodated by the narrow housing space before the ring. For the latter type of detector, we adopt a large, thin carbon foil (100 mm× 50 mm and 60 g/cm 2 ) and a large micro channel plate (MCP) (95 mm× 42 mm), which can cover the large beam profile in the Rare-RI Ring. To impinge secondary electrons produced in the carbon foil onto the MCP, we utilize two methods. One method uses crossed magnetic and electric fields [3], while the other uses only a mirror electric field. Measurements of timing resolution and detection efficiency have been performed using an alpha source and heavy-ion beams (~200 A MeV). In this contribution, we will present the design and performance of these TOF detectors.

Present status of Rare-RI Ring project in RIKEN RI Beam Factory

In the near future, short-lived and rare nuclei will be gener at d with a production rate of about one particle per day by uranium in-flight fission with an inten sity of 1 particle micro-Amp at the accelerator complex in RIBF. Our apparatus, named “Rare I Ring”, will be constructed at the downstream of an in-flight RI-beam separator BigRIPS. It consists of three main parts: an injection line, a fast response kicker system, and a cyclotr on-like storage ring. The combination of an injection line and a fast response kicker system enable s us to inject short-lived rare nuclei into the isochronous ring one by one. The isochronous ring, w hich consists of six magnetic sectors and straight sections, allows us to determine the mass with a n order of 10−6 precision for even only one particle, by measuring the revolution time of the pa rticle under the condition of precise isochronism. Here, we report the present status of this proj ect.

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...

Developments of atomic beam resonance method with RI beams

The new scheme to produce a spin‐polarized RI beam is being developed, in which the atomic beam resonance method is utilized for spin polarization. A gas‐filled chamber to stop the incoming RI ions and to drift them into vacuum area has been developed. The measurement of RI‐stopping in the gas was performed, and experiments for drifting and extracting of the stopped ions are now being performed. The status of the R&D for realizing the scheme is reported in this letter.