arXiv subjects

Y. Kawashima

Publications and source records attributed to Y. Kawashima.

18 recordsLinked to original sources

arXiv2025

Muonic X-Ray Measurement for the Nuclear Charge Distribution: the Case of Stable Palladium Isotopes

Background: The nuclear charge radius and distribution are the most fundamental quantities of the atomic nucleus. From the muonic transition energies, the absolute charge radius has been experimentally obtained, while there have been no established methods to discuss the distribution. Purpose: The muonic transition energies for five palladium isotopes with the mass number $A = 104$, $105$, $106$, $108$ and $110$ were measured. The procedure to deduce the charge radii and the method to discuss the charge distribution from the muonic transition energies are proposed. Method: The experiment was performed at the MuSIC-M1 beamline at Research Center for Nuclear Physics, Osaka University. A continuous muon beam impinged on the enriched palladium targets. Muonic X rays were measured by high-purity germanium detectors. Results: The muonic transition energies up to $4f$-$3d$ transitions were determined for five palladium isotopes. Discussion and conclusion: The root-mean-square charge radii are deduced assuming the two-parameter Fermi distribution. The charge distribution of the nucleus is discussed employing the Barrett model. The muonic transition energies of the $3d$-$2p$ transitions are crucial to discuss both the charge radius and the charge distribution.

nucl-ex↗

arXiv2025

Neutron emission following nuclear muon capture on palladium isotopes

The energy spectra of the neutrons emitted following nuclear muon capture on palladium isotopes ($A=104$, 105, 106, 108, and 110) were measured using isotopically enriched target. \item[Method] The experiment was performed at the MuSIC-M1 beamline at the Research Center for Nuclear Physics (RCNP), Osaka University. The neutrons and $γ$ rays were detected with twenty-one liquid scintillators and BaF$_2$ detectors. The time-of-flight method was used to determine the neutron energy. \item[Results] Neutron energy spectra from 1\,MeV up to 20\,MeV were measured for five palladium isotopes, providing the first systematic data in the $A\sim100$ region. The spectral shapes were compared with the previous measurement for heavy nuclei and theoretical calculations. The neutron-neutron opening angle distribution was also measured and an indication of small angle correlation was found. \item[Conclusions] The spectral shape below 4\,MeV was well explained consistently with the previous measurement by the evaporation model introducing a mass number scaling. The neutron energy spectrum around 10\,MeV plays a key role in understanding the dynamics of the nuclear muon capture reaction because it is the result of the transition from the direct and pre-equilibrium neutron emission onto the evaporation process.

nucl-ex↗

arXiv2023

Ordinary muon capture rates on $^{100}$Mo and $^{\rm nat}$Mo for astro-antineutrinos and double beta decays

\item[Background] The nuclear responses for antineutrinos associated with double beta decays (DBDs) and astro-antineutrino interactions are studied by measuring ordinary muon capture (OMC) rates. \item[Purpose]The experimental studies of absolute OMC rates and their mass number dependence for $^{100}$Mo and the natural Mo are currently of interest in astro-antineutrinos and DBDs. \item[Method]The OMC rates were obtained experimentally by measuring the time spectrum of the trapped muon's decay into electrons to obtain the half-lives of the trapped muons. \item[Results]The OMC rate for the enriched isotope of $^{100}$Mo is $Λ$($^{100}$Mo)=(7.07$\pm$0.32)$\times10^{6}$ s$^{-1}$, while that for the natural Mo is $Λ$($^{\rm nat}$Mo)=(9.66$\pm$0.44)$\times10^{6}$ s$^{-1}$, i.e., $Λ$($^{100}$Mo) is about 27$\%$ of $Λ$($^{\rm nat}$Mo), reflecting the blocking effect of the excess neutrons for the proton-to-neutron transformation in OMC. The present experimental observation is consistent with the predictions using Goulard-Primakoff's (GPs) and Primakoff's (Ps) empirical equations. \item[Conclusions] The absolute OMC rates for $^{100}$Mo and $^{\rm nat}$Mo were measured. The large neutron excess in $^{100}$Mo gives a much lower OMC rate than $^{\rm nat}$Mo. On both $^{100}$Mo and $^{\rm nat}$Mo, consistent OMC rates with the GP and P values are observed.

nucl-ex↗

arXiv2021

Low background measurement in CANDLES-III for studying the neutrino-less double beta decay of $^{48}$Ca

We developed a CANDLES-III system to study the neutrino-less double beta (0$νββ$) decay of $^{48}$Ca. The proposed system employs 96 CaF$_{2}$ scintillation crystals (305 kg) with natural Ca ($^{\rm nat.}$Ca) isotope which corresponds 350\,g of $^{48}$Ca. External backgrounds were rejected using a 4$π$ active shield of a liquid scintillator surrounding the CaF$_2$ crystals. The internal backgrounds caused by the radioactive impurities within the CaF$_2$ crystals can be reduced effectively through analysis of the signal pulse shape. We analyzed the data obtained in the Kamioka underground for a live-time of 130.4\,days to evaluate the feasibility of the low background measurement with the CANDLES-III detector. Using Monte Carlo simulations, we estimated the background rate from the radioactive impurities in the CaF$_{2}$ crystals and the rate of high energy $γ$-rays caused by the (n, $γ$) reactions induced by environmental neutrons. The expected background rate was in a good agreement with the measured rate, i.e., approximately 10$^{-3}$ events/keV/yr/(kg of $^{\rm nat.}$Ca), in the 0$νββ$ window. In conclusion, the background candidates were estimated properly by comparing the measured energy spectrum with the background simulations. With this measurement method, we performed the first search for 0$νββ$ decay in a low background condition using a detector with a Ca isotope, in which the Ca present was not enriched, in a scale of hundreds of kg. The $^{48}$Ca isotope has a high potential for use in 0$νββ$ decay search, and is expected to be useful for the development of a next-generation detector for highly sensitive measurements.

hep-ex↗

arXiv2020

Obliquity measurement and atmospheric characterization of the WASP-74 planetary system

We present new transit observations of the hot Jupiter WASP-74 b ($T_\mathrm{eq} \sim$ 1860 K) using the high-resolution spectrograph HARPS-N and the multi-colour simultaneous imager MuSCAT2. We refine the orbital properties of the planet and its host star, and measure its obliquity for the first time. The measured sky-projected angle between the stellar spin-axis and the planet's orbital axis is compatible with an orbit well-aligned with the equator of the host star ($λ= 0.77\pm0.99 \mathrm{deg}$). We are not able to detect any absorption feature of H$α$, or any other atomic spectral features, in its high-resolution transmission spectra due to low S/N at the line cores. Despite previous claims regarding the presence of strong optical absorbers such TiO and VO gases in the atmosphere of WASP-74 b, the new ground-based photometry combined with a reanalysis of previously reported observations from the literature shows a slope in the low-resolution transmission spectrum steeper than expected from Rayleigh scattering alone.

astro-ph.EP↗

arXiv2020

Mineral cloud and hydrocarbon haze particles in the atmosphere of the hot Jupiter JWST target WASP-43b

Having a short orbital period and being tidally locked makes WASP-43b an ideal candidate for JWST observations. Phase curve observations of an entire orbit will enable the mapping of the atmospheric structure across the planet, with different wavelengths of observation allowing different atmospheric depths to be seen. We provide insight into the details of the clouds that may form on WASP-43b in order to prepare the forthcoming interpretation of the JWST and follow-up data. We utilize 3D GCM results as input for a kinetic, non-equilibrium model for mineral cloud particles, and for a kinetic model to study a photochemicaly-driven hydrocarbon haze component. Mineral condensation seeds form throughout the atmosphere of WASP-43b. This is in stark contrast to the ultra-hot Jupiters, like WASP-18b and HAT-P-7b. The dayside is loaded with few but large mineral cloud particles in addition to hydrocarbon haze particles of comparable abundance. Photochemically driven hydrocarbon haze appears on the dayside, but does not contribute to the cloud formation on the nightside. The geometrical cloud extension differs across the globe due to the changing thermodynamic conditions. Day and night differ by 6000km in pressure scale height. As reported for other planets, the C/O is not constant throughout the atmosphere. The mean molecular weight is approximately constant in a H2-dominated WASP-43b. WASP-43b is expected to be fully covered in clouds which are not homogeneously distributed throughout the atmosphere. The dayside and the terminator clouds will be a combination of mineral particles of locally varying size and composition, and of hydrocarbon hazes. The optical depth of hydrocarbon hazes is considerably lower than that of mineral cloud particles such that a wavelength-dependent radius measurement of WASP-43b would be determined by the mineral cloud particles but not by hazes.

astro-ph.EP↗

arXiv2020

An electron linac with high beam intensity over 1-Ampere for disposal of radioactive waste

In order to dissipate long-lived radioactive waste, not only high ux proton accelerator but also electron linac have been proposed. A proton accelerator directly induces nuclear fission and mutation. On the other hand, electron beam has two processes: production of gamma rays through bremsstrahlung and produced gamma rays are available for the (gamma ; n) reaction. Protons dissipate nuclei and simultaneously newly produce radioisotopes of by-products. Since an electron linac produces less radioactive wastes, we focus only an electron linac with high beam intensity more than 1-Ampere. To reduce the yield of by-products for radioisotopes as less as possible, we accelerate electron beam with the energy less than 30 MeV. The accelerated beam intensity is designed to be more than 1-Ampere. To realize an electron linac with high intensity, the operation for the linac is not pulsed one, but continuous wave. To accelerate electron beam, we install higher-order-modes (HOMs) free normal conducting cavities to suppress beam instabilities.

physics.acc-ph↗

arXiv2015

An eclipsing double-line spectroscopic binary at the stellar/substellar boundary in the Upper Scorpius OB association

We aim at constraining evolutionary models at low mass and young ages by identifying interesting transiting system members of the nearest OB association to the Sun, Upper Scorpius, targeted by the Kepler mission. We produced light curves for M dwarf members of the USco region surveyed during the second campaign of the Kepler K2 mission. We identified 'by eye' a transiting system, UScoJ161630.68-251220.1 (=EPIC203710387) with a combined spectral type of M5.25 whose photometric, astrometric, and spectroscopic properties makes it a member of USco. We conducted an extensive photometric and spectroscopic follow-up of this transiting system with a suite of telescopes and instruments to characterise the properties of each component of the system. We calculated a transit duration of about 2.42 hours occuring every 2.88 days with a slight difference in transit depth and phase between the two components. We estimated a mass ratio of 0.922+/-0.015 from the semi-amplitudes of the radial velocity curves for each component. We derived masses of 0.091+/-0.005 Msun and 0.084+/-0.004 Msun,radii of 0.388+/-0.008 Rsun and 0.380+/-0.008 Rsun, luminosities of log(L/Lsun)=-2.020 (-0.121+0.099) dex and -2.032 (-0.121+0.099) dex, and effective temperatures of 2901 (-172+199) K and 2908 (-172+199) K for the primary and secondary, respectively. We present a complete photometric and radial velocity characterisation of the least massive double-line eclipsing binary system in the young USco association with two components close to the stellar/substellar limit. This system fills in a gap between the least massive eclipsing binaries in the low-mass and substellar regimes at young ages and represents an important addition to constrain evolutionary models at young ages.

astro-ph.SR↗

arXiv2012

Large-scale length that determines the mean rate of energy dissipation in turbulence

The mean rate of energy dissipation in turbulence is traditionally assumed to scale with parameters of the energy-containing large scales, i.e., the root-mean-square fluctuation of the longitudinal velocity u and its correlation length L(u). However, the resultant scaling coefficient C(u) is known to depend on the large-scale configuration of the flow. We define the correlation length L(u2) of the local energy u2, study the scaling coefficient C(u2) with experimental data of several flows, and find a possibility that C(u2) does not depend on the flow configuration. Not L(u) but rather L(u2) could scale with the typical size of the energy-containing eddies, so that L(u2) determines the mean rate at which the energy is transferred from those eddies to the smaller eddies and is eventually dissipated into heat. The independence from the flow configuration is also found for the two-point correlations and so on if L(u2) is used to normalize the scale.

physics.flu-dyn↗

arXiv2011

Statistical mechanics and large-scale velocity fluctuations of turbulence

Turbulence exhibits significant velocity fluctuations even if the scale is much larger than the scale of the energy supply. Since any spatial correlation is negligible, these large-scale fluctuations have many degrees of freedom and are thereby analogous to thermal fluctuations studied in the statistical mechanics. By using this analogy, we describe the large-scale fluctuations of turbulence in a formalism that has the same mathematical structure as used for canonical ensembles in the statistical mechanics. The formalism yields a universal law for the energy distribution of the fluctuations, which is confirmed with experiments of a variety of turbulent flows. Thus, through the large-scale fluctuations, turbulence is related to the statistical mechanics.

physics.flu-dyn↗

arXiv2007

Laboratory experiments for intense vortical structures in turbulence velocity fields

Vortical structures of turbulence, i.e., vortex tubes and sheets, are studied using one-dimensional velocity data obtained in laboratory experiments for duct flows and boundary layers at microscale Reynolds numbers from 332 to 1934. We study the mean velocity profile of intense vortical structures. The contribution from vortex tubes is dominant. The radius scales with the Kolmogorov length. The circulation velocity scales with the rms velocity fluctuation. We also study the spatial distribution of intense vortical structures. The distribution is self-similar over small scales and is random over large scales. Since these features are independent of the microscale Reynolds number and of the configuration for turbulence production, they appear to be universal.

physics.flu-dyn↗

arXiv2005

On Landau's prediction for large-scale fluctuation of turbulence energy dissipation

Kolmogorov's theory for turbulence in 1941 is based on a hypothesis that small-scale statistics are uniquely determined by the kinematic viscosity and the mean rate of energy dissipation. Landau remarked that the local rate of energy dissipation should fluctuate in space over large scales and hence should affect small-scale statistics. Experimentally, we confirm the significance of this large-scale fluctuation, which is comparable to the mean rate of energy dissipation at the typical scale for energy-containing eddies. The significance is independent of the Reynolds number and the configuration for turbulence production. With an increase of scale r above the scale of largest energy-containing eddies, the fluctuation becomes to have the scaling r^-1/2 and becomes close to Gaussian. We also confirm that the large-scale fluctuation affects small-scale statistics.

physics.flu-dyn↗

arXiv2004

Vortex Tubes in Turbulence Velocity Fields at Reynolds Numbers 300-1300

The most elementary structures of turbulence, i.e., vortex tubes, are studied using velocity data obtained in a laboratory experiment for boundary layers with microscale Reynolds numbers 295-1258. We conduct conditional averaging for enhancements of a small-scale velocity increment and obtain the typical velocity profile for vortex tubes. Their radii are of the order of the Kolmogorov length. Their circulation velocities are of the order of the root-mean-square velocity fluctuation. We also obtain the distribution of the interval between successive enhancements of the velocity increment as the measure of the spatial distribution of vortex tubes. They tend to cluster together below about the integral length and more significantly below about the Taylor microscale. These properties are independent of the Reynolds number and are hence expected to be universal.

physics.flu-dyn↗

arXiv2003

Probability density function of turbulent velocity fluctuations in rough-wall boundary layer

The probability density function of single-point velocity fluctuations in turbulence is studied systematically using Fourier coefficients in the energy-containing range. In ideal turbulence where energy-containing motions are random and independent, the Fourier coefficients tend to Gaussian and independent of each other. Velocity fluctuations accordingly tend to Gaussian. However, if energy-containing motions are intermittent or contaminated with bounded-amplitude motions such as wavy wakes, the Fourier coefficients tend to non-Gaussian and dependent of each other. Velocity fluctuations accordingly tend to non-Gaussian. These situations are found in our experiment of a rough-wall boundary layer.

physics.flu-dyn↗

arXiv2002

Vortex tubes in velocity fields of laboratory isotropic turbulence: dependence on the Reynolds number

The streamwise and transverse velocities are measured simultaneously in isotropic grid turbulence at relatively high Reynolds numbers, Re(lambda) = 110-330. Using a conditional averaging technique, we extract typical intermittency patterns, which are consistent with velocity profiles of a model for a vortex tube, i.e., Burgers vortex. The radii of the vortex tubes are several of the Kolmogorov length regardless of the Reynolds number. Using the distribution of an interval between successive enhancements of a small-scale velocity increment, we study the spatial distribution of vortex tubes. The vortex tubes tend to cluster together. This tendency is increasingly significant with the Reynolds number. Using statistics of velocity increments, we also study the energetical importance of vortex tubes as a function of the scale. The vortex tubes are important over the background flow at small scales especially below the Taylor microscale. At a fixed scale, the importance is increasingly significant with the Reynolds number.

physics.flu-dyn↗

arXiv2002

Probability density function of turbulent velocity fluctuation

The probability density function (PDF) of velocity fluctuations is studied experimentally for grid turbulence in a systematical manner. At small distances from the grid, where the turbulence is still developing, the PDF is sub-Gaussian. At intermediate distances, where the turbulence is fully developed, the PDF is Gaussian. At large distances, where the turbulence has decayed, the PDF is hyper-Gaussian. The Fourier transforms of the velocity fluctuations always have Gaussian PDFs. At intermediate distances from the grid, the Fourier transforms are statistically independent of each other. This is the necessary and sufficient condition for Gaussianity of the velocity fluctuations. At small and large distances, the Fourier transforms are dependent.

physics.flu-dyn↗

arXiv2001

Timing System of SPring-8 Booster Synchrotron

The timing system of SPring-8 booster synchrotron generates various timing signals concerning beam injection, acceleration from 1 GeV to 8 GeV and ejection. We have improved the timing system of the synchrotron giving it better stability and flexibility. This improvement results the other merits of advanced operations, for example, storing electron beam in the synchrotron, changing the injection cycle from 1 Hz to the slower frequency to increase the RF knock-out (RF-KO) operation period and ejecting the low energy beam during ramping up.

physics.acc-ph↗

arXiv2000

Vortex tubes in velocity fields of laboratory isotropic turbulence

The streamwise and transverse velocities are measured simultaneously in grid turbulence at Reynolds numbers 100-300. We extract typical intermittency patterns, which are consistent with velocity profiles of Burgers and Lamb-Oseen vortices. The radii of these vortex tubes are estimated to be several of the Kolmogorov length.

physics.flu-dyn↗