K. Asahi

The RIKEN radioactive beam facility

Abstract A radioactive beam facility based on projectile fragmentation, RIPS, has been constructed at RIKEN to enable radioactive-beam experiments. The facility is characterized by the production of high-intensity beams and spin-polarized beams. Since the beginning of 1990, experiments on exotic nuclei have been extensively performed exploiting these useful features. The characteristics and the present status of the RIPS are described.

New aspect of intermediate energy heavy ion reactions. Large spin polarization of fragments

Abstract The spin polarization, P , of 12 B ejectiles has been measured for projectile fragmentation reactions induced by a 40.6 MeV/u 14 N beam. Large values of P were observed, showing a characteristic dependence on the outgoing momentum including a sign change occurring at a momentum corresponding to the beam velocity. This behavior corresponds well with simple kinematical arguments based on projectile fragmentation models.

Systematic behavior of ejectile spin polarization in the projectile fragmentation reaction

Abstract Ejectile spin polarization P in intermediate-energy projectile fragmentation has been measured for different targets and incident energies using the RIPS fragment separator at RIKEN. The observed P as a function of the fragment momentum shows a systematic change when the atomic number of the target or the incident energy is varied. Most remarkably, P does not vanish at the momentum corresponding to the beam velocity, indicating an important effect which has not been considered in the previously proposed model.

Measurement of the magnetic moments of 14B and 15B using projectile fragmentation spin polarization

Abstract By making use of the phenomenon of ejectile spin polarization in the projectile fragmentation reaction as a tool to produce polarized radioactive nuclei, the magnetic moments of 14B and 15B have been determined by the β-NMR measurement, to be μ( 14 B ) = (1.185±0.005) μn and μ( 15 B ) = (2.659±0.015) μn where μn is the nuclear magneton. The comparison of the results with shell model calculations suggests that the single-particle energy of the neutron s 1 2 orbit shifts downwards considerably compared with the d 5 2 orbit in 14B, and also indicates the importance of Jπ = 2+ configurations of neutrons in the sd shell. Thus, it is demonstrated that the measurement of magnetic moments provides useful information on the nuclear structure in the newly accessible region of light-mass unstable nuclei.

Probing exotic phenomena at the interface of nuclear and particle physics with the electric dipole moments of diamagnetic atoms: A unique window to hadronic and semi-leptonic CP violation

Abstract.The current status of electric dipole moments of diamagnetic atoms which involves the synergy between atomic experiments and three different theoretical areas, i.e. particle, nuclear and atomic, is reviewed. Various models of particle physics that predict CP violation, which is necessary for the existence of such electric dipole moments, are presented. These include the standard model of particle physics and various extensions of it. Effective hadron level combined charge conjugation (C) and parity (P) symmetry violating interactions are derived taking into consideration different ways in which a nucleon interacts with other nucleons as well as with electrons. Nuclear structure calculations of the CP-odd nuclear Schiff moment are discussed using the shell model and other theoretical approaches. Results of the calculations of atomic electric dipole moments due to the interaction of the nuclear Schiff moment with the electrons and the P and time-reversal (T) symmetry violating tensor-pseudotensor electron-nucleus are elucidated using different relativistic many-body theories. The principles of the measurement of the electric dipole moments of diamagnetic atoms are outlined. Upper limits for the nuclear Schiff moment and tensor-pseudotensor coupling constant are obtained combining the results of atomic experiments and relativistic many-body theories. The coefficients for the different sources of CP violation have been estimated at the elementary particle level for all the diamagnetic atoms of current experimental interest and their implications for physics beyond the standard model is discussed. Possible improvements of the current results of the measurements as well as quantum chromodynamics, nuclear and atomic calculations are suggested.

Nuclear spin maser with an artificial feedback mechanism

Abstract We describe a scheme for nuclear spin maser which has an artificial feedback to the nuclear spins to bring about a self-sustained nuclear spin precession and thus to allow unlimitedly long observation times for precession. This scheme can operate under lower applied fields and smaller spin densities than the conventional spin maser scheme. Its operation was experimentally tested by using a spin-polarized 129 Xe gas as a model substance. The frequency fluctuation and other basic properties were analyzed based on the modified Bloch equations.

Electric quadrupole moments of neutron-rich nuclei 14B and 15B

Abstract Spin-polarized fragments 14B and 15B produced in intermediate-energy projectile fragmentation reactions were implanted in a Mg single crystal, and the electric quadrupole moments Q for 14B and 15B were determined by β-NMR spectroscopy. The results, |Q( 14 B)| = 29.84 ± 0.75 mb and |Q( 15 B)| = 38.01 ± 1.08 mb , are compared wi models. Shell-model calculations with 0ωω model space, using effective charges commonly accepted in this mass region, predict values about 40 % larger than the experimental Q (15B). Agreement is obtained when a much smaller effective charge for neutrons is employed. The Q (14B) sensitively reflects small admixture of the d 3 2 neutron configuration and, when combined with the previously obtained data for the magnetic moment, determines reliably the ground state wave function of 14B.

Spin alignment of43Sc produced in the fragmentation of 500 MeV/u46Ti

In the fragmentation of 500 MeV/u46Ti the spin alignment of43mSc (I=19/2−, T1/2=473 ns) fragments was observed by the Time Dependent Perturbed Angular Distribution (TDPAD) method. The measurement was performed for different cuts in the longitudinal momentum distribution. A positive spin alignment of about 35% was observed in the center and a negative alignment of about 15% in the wing of the distribution. For the different cuts the relative production of the 19/2− state was measured. In the wing of the distribution the isomeric ratio N(19/2−)/total43Sc is about 15 times larger than in the center. The results of this pilot experiment are discussed in the frame of a shell-model.

MAGNETIC MOMENT AND ELECTRIC QUADRUPOLE MOMENT OF THE 18N GROUND STATE

Abstract The magnetic moment and electric quadrupole moment of a neutron-rich nucleus 18 N have been determined by the β-NMR method, taking advantage of the fragment spin polarization induced in the intermediate-energy projectile fragmentation reaction. To assure the existence of a sufficient polarization prior to the resonance search, a scheme of polarization measurement by means of an adiabatic field rotation has been developed and successfully incorporated in the β-NMR experiment. From the observed resonance in a Pt stopper the magnetic moment for the 18 N ground state has been determined to be |μ|=0.3279±0.0013μN. The 18 N fragments have also been implanted in a single crystal Mg stopper, and from the observed quadrupole frequency |eqQ/h|=73.2±1.4 kHz, the electric quadrupole moment |Q|=12.3±1.2 mb has been deduced. The obtained μ and Q are compared with shell model calculations.

Polarized3He system for T- and P-violation neutron experiments

We have constructed an apparatus to polarize the3He nuclear spin, which will be used as a neutron spin analyzer in T- and P-violation neutron experiments. We report on principles and the present status of the method for the polarization of3He and the determination of its value.