A. Yoshimi

Identification of 45 New Neutron-Rich Isotopes Produced by In-Flight Fission of a 238U Beam at 345 MeV/nucleon

A search for new isotopes using in-flight fission of a 345 MeV/nucleon 238 U beam has been carried out at the RI Beam Factory at the RIKEN Nishina Center. Fission fragments were analyzed and identi...

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.

Externally triggered coherent two-photon emission from hydrogen molecules

We report coherent enhancement of two-photon emission from the excited vibrational state of molecular hydrogen triggered by irradiating mid-infrared pulses externally. We previously observed the two-photon emission triggered by the internally generated fourth Stokes photons. By injecting independent mid-infrared pulses externally, it is possible to control experimental parameters and investigate the mechanism in more detail. In this article, we describe the two-photon emission using the external trigger pulses. Its spectrum and dependence on the energy and timing of the trigger pulse are presented along with numerical simulations based on the Maxwell-Bloch equations. The measured number of emitted photons is 6 10^11 photons/pulse and the resulting enhancement factor from the spontaneous emission is more than 10^18. This value is three orders of magnitude higher than that of the previous experiment. External control of emission process is expected to be essential for observation of weaker process of radiative emission of neutrino pair.

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

Precision measurement of the electric quadrupole moment of 31Al and determination of the effective proton charge in the sd-shell

Abstract 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 .

Production of Ba Metastable State via Superradiance

We describe in this paper a fast and efficient method of producing a high density of barium (Ba) atoms in the 1D2 metastable state, which is a candidate initial state for a new class of cooperative and coherent optical process called paired superradiance (PSR). In the experiment, Ba atoms are excited first by laser light to the 1P1 state and then brought to the desired state 1D2 via radiative transition in the superradiance (SR) mode. It is found that a production efficiency (from 1S0 to 1D2) of more than ∼30% is achieved within a time interval of a few nanoseconds for a Ba density n > 1019 m−3. Several key features of SR important for future PSR experiments are also studied.

Simultaneous Measurements of Superradiance at Multiple Wavelength from Helium Excited States: II. Analysis

Previous experimental studies of superradiance (SR) in multi-level systems have been explainable using the predictions of the well-known simple two-level SR model. However our recent study [K. Nakajima et al., J. Phys. Soc. Jpn. 84, 054301 (2015)] using EUV free-electron laser excitation of helium atoms, where SR was observed at wavelengths of 502, 668, and 728 nm, revealed behaviour which necessitates a full multi-level treatment of the SR development. In this paper, we report simulations of the initial excitation by the FEL pulses, and the subsequent development of multi-level SR. The results of the simulation reproduce the experimental findings, and reveal that competitive SR on two transitions with a common upper level plays an important role in the development of the system.

Search for electric dipole moment in 129Xe atom using a nuclear spin oscillator

We aim to measure the electric dipole moment (EDM) of a diamagnetic atom 129Xe using an optical-detection nuclear spin maser technique. The relation of EDM in a diamagnetic atom to nuclear Schiff moment and fundamental sources generating it is discussed, and the present status for the development of our experimental setup is presented.

Coherence decay measurement of v = 2 vibrons in solid parahydrogen

The coherence decay of the v = 2 vibrational state (vibrons) of solid parahydrogen was measured via time-resolved coherent anti-Stokes Raman spectroscopy. We found that the decay curve has a non-exponential time profile in the time scale of 200 ns at a low temperature below 5 K and a low orthohydrogen impurity concentration (~0.01%). This behavior, as also observed in the case of the v = 1 vibrons, represents a signature of band structure of the v = 2 state in the solid phase. The maximum coherence decay time of 50 ns in an exponential part was achieved, which shows excellence of the v = 2 state for coherent processes. We also found that finite temperatures, orthohydrogen impurities, and other structural inhomogeneity accelerate the decay, hiding the non-exponential feature of the vibron band.

Nuclear Spin Maser at Highly Stabilized Low Magnetic Field and Search for Atomic EDM

A nuclear spin maser is operated at a low static field through an active feedback scheme based on an optical nuclear spin detection and succeeding spin control by a transverse field application. The frequency stability of this optical‐coupling spin maser is improved by installation of a low‐noise current source for a solenoid magnet producing a static magnetic field in the maser operation. Experimental devices for application of the maser to EDM experiment are being developed.