Okada Kunihiro

We observed and directly measured the M1 transition between the two states of the fine structure splitting in the ground state of Ba7+ with a visible spectrometer coupled to a compact electron beam ion trap. To validate the measurement accuracy, we demonstrated a calibration method using Ar+ emissions from buffer gas. The wavenumber in vacuum was determined to be 23591.57 (15) cm−1.

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The masses of Es246, Fm251, and the transfermium nuclei Md249-252 and No254, produced by hot- and cold-fusion reactions, in the vicinity of the deformed N=152 neutron shell closure, have been directly measured using a multireflection time-of-flight mass spectrograph. The masses of Es246 and Md249,250,252 were measured for the first time. Using the masses of Md249,250 as anchor points for α decay chains, the masses of heavier nuclei, up to Bh261 and Mt266, were determined. These new masses were compared with theoretical global mass models and demonstrated to be in good agreement with macroscopic-microscopic models in this region. The empirical shell gap parameter δ2n derived from three isotopic masses was updated with the new masses and corroborates the existence of the deformed N=152 neutron shell closure for Md and Lr.

We present visible spectra of highly charged holmium ions, which is a potential candidate ion for constructing a precise atomic clock. A compact electron beam ion trap is used for producing and trapping holmium ions. By observing electron energy dependence of the spectra, the charge state is assigned for each emission line. We also present theoretical transition frequency and amplitude obtained with two different methods. (C) 2017 Elsevier B.V. All rights reserved.

Synopsis We demonstrated photodissociation of sympathetically crystallized CaH+ toward rovibrational spectroscopy by UVUV or IR-UV double resonance. The photodissociation of CaH+ was successfully confirmed at l = 283-287 nm.

Cold polar molecules are key to both the understanding of fundamental physics and the characterization of the chemical evolution of interstellar clouds. To facilitate such studies over a wide range of temperatures, we developed a new type of Stark velocity filter for changing the translational and rotational temperatures of velocity-selected polar molecules without changing the output beam position. The translational temperature of guided polar molecules can be significantly varied by exchanging the wavy deflection section with one having a different radius of the curvature and a different deflection angle. Combining in addition a temperature variable gas cell with thewavy Stark velocity filter enables to observe the translational and rotational temperature dependence of the reaction-rate constants of cold ion-polar molecule reactions over the interesting temperature range of 10-100 K. Published by AIP Publishing.

We describe the present status of future high-precision measurements of nuclear g-factors utilizing laser microwave double and laser-microwave-rf triple resonance methods for online-trapped, laser-cooled radioactive beryllium isotope ions. These methods have applicability to other suitably chosen isotopes and for beryllium show promise in deducing the hyperfine anomaly of Be-11 with a sufficiently high precision to study the nuclear magnetization distribution of this one-neutron halo nucleus in a nuclear model-independent manner. (C) 2015 Elsevier B.V. All rights reserved.

We performed classical molecular dynamics (MD) simulations in order to search the conditions for efficient sympathetic cooling of highly charged ions (HCIs) in a linear Paul trap. Small two-component ion Coulomb crystals consisting of laser-cooled ions and HCIs were characterized by the results of the MD simulations. We found that the spatial distribution is determined by not only the charge-to-mass ratio but also the space charge effect. Moreover, the simulation results suggest that the temperature of HCIs do not necessarily decrease with increasing the number of laser-cooled ions in the cases of linear ion crystals. We also determined the cooling limit of sympathetically cooled Ho-165(14+) ions in small linear ion Coulomb crystals. The present results show that sub-milli-Kelvin temperatures of at least 10 Ho14+ ions will be achieved by sympathetic cooling with a single laser-cooled Be+.

We performed classical molecular dynamics (MD) simulations in order to search the conditions for efficient sympathetic cooling of highly charged ions (HCIs) in a linear Paul trap. Small two-component ion Coulomb crystals consisting of laser-cooled ions and HCIs were characterized by the results of the MD simulations. We found that the spatial distribution is determined by not only the charge-to-mass ratio but also the space charge effect. Moreover, the simulation results suggest that the temperature of HCIs do not necessarily decrease with increasing the number of laser-cooled ions in the cases of linear ion crystals. We also determined the cooling limit of sympathetically cooled 165Ho14+ ions in small linear ion Coulomb crystals. The present results show that sub-milli-Kelvin temperatures of at least 10 Ho14+ ions will be achieved by sympathetic cooling with a single laser-cooled Be+.

We demonstrate the application of reliable methods to determine both the average micromotion energies and the number of sympathetically cooled ions (SCIs) embedded in mixed-ion Coulomb crystals in a linear Paul trap. The number of the SCIs and the micromotion energies for the observed mixed-ion crystals are determined by comparing experimentally obtained images with molecular-dynamics simulations, where the kinetic energies of SCIs trapped in rf fields are averaged in cold elastic collisions between the laser-cooled ions and virtual very light atoms. This combined method quickly achieves the quasiequilibrium state of large mixed Coulomb crystals with over 10(3) ions, regardless of the initial conditions, and shows that the previously used pseudopotential-based adiabatic approximations should be replaced by such molecular-dynamics simulations. In addition, a pattern-matching recognition procedure is introduced which objectively ascertains the number of ions. We also apply the presented characterization method to determine the reaction-rate constant between slow acetonitrile molecules and sympathetically cooled Ne+ ions at a translational temperature lower than 10 K.

We have developed a Kingdon ion trap system for the purpose of the laboratory observation of the x-ray forbidden transitions of highly charged ions (HCIs). Externally injected Arq+ (q = 5-7) with kinetic energies of 6q keV were successfully trapped in the ion trap. The energy distribution of trapped ions is discussed in detail on the basis of numerical simulations. The combination of the Kingdon ion trap and the time-of-flight mass spectrometer enabled us to measure precise trapping lifetimes of HCIs. As a performance test of the instrument, we measured trapping lifetimes of Arq+ (q = 5-7) under a constant number density of H-2 and determined the charge-transfer cross sections of Arq+ (q = 5, 6)-H-2 collision systems at binary collision energies of a few eV. It was confirmed that the present cross section data are consistent with previous data and the values estimated by some scaling formula. (C) 2014 AIP Publishing LLC.

We have developed a Kingdon ion trap system for the purpose of the laboratory observation of the x-ray forbidden transitions of highly charged ions (HCIs). Externally injected Arq+ (q = 5-7) with kinetic energies of 6q keV were successfully trapped in the ion trap. The energy distribution of trapped ions is discussed in detail on the basis of numerical simulations. The combination of the Kingdon ion trap and the time-of-flight mass spectrometer enabled us to measure precise trapping lifetimes of HCIs. As a performance test of the instrument, we measured trapping lifetimes of Arq+ (q = 5-7) under a constant number density of H2 and determined the charge-transfer cross sections of Arq+(q = 5, 6)-H2 collision systems at binary collision energies of a few eV. It was confirmed that the present cross section data are consistent with previous data and the values estimated by some scaling formula.

We experimentally demonstrated that the stability of an atomic clock improves at its fastest rate tau(-1) (where tau is the averaging time) when the phase of a local oscillator is genuinely compared to the continuous phase of many atoms in a single trap (an atomic phase lock). For this demonstration, we developed a simple method that repeatedly monitors the atomic phase while retaining its coherence by observing only a portion of the whole ion cloud. Using this new method, we measured the continuous phase over three measurement cycles, and thereby improved the stability scaling from tau(-1/2) to tau(-1) during the three measurement cycles. This simple method provides a path by which atomic clocks can approach a quantum projection noise limit, even when the measurement noise is dominated by the technical noise.

The hyperfine splittings of ground state Be-11(+) have been measured precisely by laser-microwave double resonance spectroscopy for trapped and laser cooled beryllium ions. The ions were produced at relativistic energies and subsequently slowed down and trapped at mK temperatures. The magnetic hyperfine structure constant of Be-11(+) was determined to be A(11) = -2677.302988(72) MHz from the measurements of the m(F) -m(F)' = 0-0 field independent transition. This measurement provides essential data for the study of the distribution of the halo neutron in the single neutron halo nucleus Be-11 through the Bohr-Weisskopf effect.

A multi-reflection time-of-flight (MRTOF) mass spectrograph has been implemented at RIKEN to provide high-precision mass measurements of very short-lived nuclei. Of particular interest are mass measurements of r-process nuclei and trans-uranium nuclei. In such nuclei, the MRTOF can perform on par with or better than traditional Penning trap systems. We demonstrate that the MRTOF-MS is capable of accurately attaining relative mass precision of δm/m<10-7 and describe it's utility with heavy, short-lived nuclei.© 2013 Elsevier B.V. All rights reserved.

A radiofrequency quadrupole ion trap system for use with a multi-reflection time-of-flight mass spectrograph (MRTOF) for short-lived nuclei has been developed. The trap system consists of two different parts, an asymmetric taper trap and a flat trap. The ions are cooled to a sufficient small bunch for precise mass measurement with MRTOF in only 2 ms cooling time in the flat trap, then orthogonally ejected to the MRTOF for mass analysis. A trapping efficiency of approximate to 27% for Na-23(+) and approximate to 5.1% for Li-7(+) has been achieved. (C) 2013 Elsevier B.V. All rights reserved.

A multireflection time-of-flight mass spectrograph, competitive with Penning trap mass spectrometers, has been built at RIKEN. We have performed a first online mass measurement, using 8Li+ (T1/2=838 ms). A new analysis method has been realized, with which, using only 12C+ references, the mass excess of 8Li was accurately determined to be 20 947.6(15)(34) keV (δm/m=6.6×10-7). The speed, precision, and accuracy of this first online measurement exemplifies the potential for using this new type of mass spectrograph for precision measurements of short-lived nuclei. © 2013 American Physical Society.

We have developed a combined Stark-velocity-filter-ion-trap apparatus for the purpose of reaction-rate measurements between cold trapped ions and slow polar molecules under ultrahigh vacuum conditions. The prerequisite steps such as the characterization of velocity-selected polar molecules (PM), namely ND3, H2CO, and CH3CN, were performed using time-of-flight (TOF) measurements. We confirmed the generation of slow ND 3, H2CO, and CH3CN molecules having thermal energies of a few Kelvin. Additionally, the number densities of the slow velocity-filtered polar molecules were determined to be in the range of n=104 to 106 cm-3 by calibrating the TOF signals. In a first experiment, the Stark velocity filter was connected to a cryogenic linear Paul trap and reaction-rate measurements between laser-cooled Ca+ Coulomb crystals and velocity-selected polar molecules were carried out. The observed reaction rates are of the order of 10-5 s-1, which are much slower than typical reaction rates of molecular ion-polar-molecule reactions at low temperatures. The present results confirm that reaction-rate measurements between velocity-selected polar molecules and sympathetically cooled molecular ions cooled by a laser-cooled Ca+ Coulomb crystal can be performed. Next we measured the reaction rates between sympathetically cooled nonfluorescent stored ion molecules namely N2H+ ions and velocity-selected CH3CN molecules at the average reaction energy of about 3 K. The measured reaction rate of 2.0(2)×10-3 s -1 is much faster than those of the Ca++PM reactions. This is strong evidence that the velocity-selected polar molecules undergo reactive collisions. We also confirmed that the present reaction-rate constant of CH 3CN+N2H+ → CH3CNH ++N2 is consistent with the estimated values from the room temperature results and the trajectory-scaling formula of Su In the future, the present velocity-filter combined cryogenic trap apparatus will enable us to perform systematic measurements of cold ion-polar-molecule reactions, which are important problems from a fundamental viewpoint and also contribute to astrochemistry. © 2013 American Physical Society.

For trans-uranium elements, stable atomic isobars do not exist. In order to provide isobaric reference ions for the mass measurement of trans-uranium elements, an electrospray ion source (ESI) was combined with an rf-carpet to collect molecular ions efficiently. The rf-carpet allows for simplification of the pumping system to transport ions from the ESI to a precision mass analyzer. Molecular ions appropriate for isobaric references of trans-uranium elements were extracted from the rf-carpet and analyzed by a multi-reflection time-of-flight mass spectrograph (MRTOF-MS) with a resolving power of R m ≳ 100, 000. © 2012 Elsevier B.V. All rights reserved.

A Stark velocity filter has been developed for studying molecular ion-polar molecule reactions at very low temperatures. We have successfully produced slow polar molecules of ND3, NH3 and CH2O with a peak velocity of lower than 40 m/s. The property of the Stark velocity filter was systematically studied by changing the Stark voltage, the nozzle pressure and the source gas temperature. Finally the number density of the extracted slow molecules was determined. © Published under licence by IOP Publishing Ltd.

We have investigated laser-induced reactions between laser-cooled crystallized Ca+ ions and polar molecule NH3 at room temperature. Reaction rates of Ca+* (3d 2D 3/2, 4p 2P1/2) + NH3 → products have been determined from time variation of the size of fluorescence images of Ca+ Coulomb crystals. From the pressure dependence of the reaction rates we determined a lower limit of the reaction rate coefficients. © Published under licence by IOP Publishing Ltd.

We investigated sympathetic Coulomb crystallization of CaH+ ions produced by a laser-induced reaction through an excited state according to Ca-40(+)(4p(2)P(1/2)) + H-2 -&gt; (CaH+)-Ca-40 + (H center dot CaH+)-Ca-40 ions stored in a linear Paul trap were characterized by their secular-motion excitation spectrum and by the modified fluorescence images of crystallized Ca+ ions. The number of two-species crystallized ions, the secular motion temperature, and the structure were determined by molecular dynamics simulations. Both the observed two-species ion crystals and simulation images demonstrate that the CaH+ ions were sympathetically crystallized with their secular-motion temperature being less than 10 mK. We determined reaction rates from fluorescence images of two-species Coulomb crystals by systematically changing the reaction time. In addition a lower limit for the reaction rate coefficient k = 8 x 10(-10) cm(3)/s was obtained.

Precision optical spectroscopy of radioactive Be isotopes produced in projectile fragmentation has been performed for the first time at the prototype SLOWRI facility of RIKEN RI-Beam Factory. The ground state hyperfine constants of 7Be+ and 11Be+ were determined with relative accuracies of 6 × 10-7 and 3 × 10-8, respectively, by laser-microwave double resonance spectroscopy of laser-cooled ions in a trap. The optical transition energies from the ground S-state to the excited P-state of Be isotope ions were also measured to determine the nuclear charge radii from the isotope shifts. Development of the universal slow RI-beam facility-SLOWRI-based on the rf-carpet ion guide technique is progressing at RIKEN RI-beam factory. An additional capability of providing parasitic slow RI-beams from the projectile fragment separator BigRIPS is also discussed. © 2011 Springer Science+Business Media B.V.

Development of a universal slow RI-beam facility based on rf-carpet ion guide technique is being progressing at RIKEN RI-beam factory. With a prototype setup, precision optical spectroscopy experiments were performed for beryllium isotopes. An additional capability of providing parasitic slow RI-beams from the projectile fragment separator BigRIPS is also discussed.