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Ishikawa, T.

Publications and source records attributed to Ishikawa, T..

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Toward operation of series IDs at BL43LXU of SPring-8

This paper discusses two issues relating to using 3 small gap insertion devices in series at BL43LXU of SPring-8 to make a uniquely powerful source in the 15-26 keV region of the x-ray spectrum. The issues discussed are (1) damage to the covers of the downstream IDs by radiation from the upstream IDs and (2) proper steering of the electron beam to get the best photon beam properties. After tests in several configurations, including one where an ID was run without an impedance-reducing cover, the damage issue was solved by installing a distributed absorber in the most downstream ID. The steering issues were mostly resolved by the introduction of appropriate corrector magnets and feedback. The paper is written from the viewpoint of an interested beamline scientist impressed with the cooperation of different groups to make a source for new science possible.

43 PARTICLE ACCELERATORS↗
DOE OSTI2016

Proton imaging of an electrostatic field structure formed in laser-produced counter-streaming plasmas

Here, we report the measurements of electrostatic field structures associated with an electrostatic shock formed in laser-produced counter-streaming plasmas with proton imaging. The thickness of the electrostatic structure is estimated from proton images with different proton kinetic energies from 4.7 MeV to 10.7 MeV. The width of the transition region is characterized by electron scale length in the laser-produced plasma, suggesting that the field structure is formed due to a collisionless electrostatic shock.

42 ENGINEERING↗
DOE OSTI2016

Transportation of a radioactive ion beam for precise laser-trapping experiments

Francium is the heaviest species among the alkali elements. Due to its properties, francium is said to be of advantage in measurements of tiny observations, such as atomic parity violation and electric dipole moment. Before executing experiments with francium, it must be produced artificially because it is one of the most unstable elements. We produced francium with the nuclear fusion reaction of an oxygen beam and gold target, ionized the produced francium through a thermal ionization process, and extracted the ion with electrostatic fields. However, the thermal ionization process is known to ionize not only an objective atom but also other atomic species. Therefore, a Wien filter was installed to analyze the composition of the ion beam and purify the beam. This allowed us to improve the beam purity from ∼10{sup −6} to ∼10{sup −3}.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

KamLAND SENSITIVITY TO NEUTRINOS FROM PRE-SUPERNOVA STARS

In the late stages of nuclear burning for massive stars (M > 8 M{sub ⊙}), the production of neutrino–antineutrino pairs through various processes becomes the dominant stellar cooling mechanism. As the star evolves, the energy of these neutrinos increases and in the days preceding the supernova a significant fraction of emitted electron anti-neutrinos exceeds the energy threshold for inverse beta decay on free hydrogen. This is the golden channel for liquid scintillator detectors because the coincidence signature allows for significant reductions in background signals. We find that the kiloton-scale liquid scintillator detector KamLAND can detect these pre-supernova neutrinos from a star with a mass of 25 M{sub ⊙} at a distance less than 690 pc with 3σ significance before the supernova. This limit is dependent on the neutrino mass ordering and background levels. KamLAND takes data continuously and can provide a supernova alert to the community.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Local structure analysis of diluted magnetic semiconductor Co and Al co-doped ZnO nanoparticles

In this study, Co and Al ions co-doped ZnO nanoparticles (Zn(Al, Co)O NPs) were prepared by our original chemical preparation method. The obtained samples prepared by this method, were encapsulated in amorphous SiO{sub 2}. X-ray diffraction (XRD) results showed Zn(Al, Co)O NPs had a single-phase nature with hexagonal wurtzite structure. These particle sizes could be controlled to be approximately 30 nm. We investigate the effect that the increase in the carrier has on the magnetization by doping Al to Co-doped ZnO NPs. The local structures were qualitatively analyzed using X-ray absorption fine structure (XAFS) measurements.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Search for the proton decay mode with KamLAND

We present a search for the proton decay mode $p \rightarrow \bar{v}K^+$ based on an exposure of 8.97 kton-years in the KamLAND experiment. The liquid scintillator detector is sensitive to successive signals from $p \rightarrow \bar{v}K^+$ with unique kinematics, which allow us to achieve a detection efficiency of 44%, higher than previous searches in water Cherenkov detectors. We find no evidence of proton decays for this mode. The expected background, which is dominated by atmospheric neutrinos, is 0:9 ± 0.2 events. The nonbackground-subtracted limit on the partial proton lifetime is τΒ($p \rightarrow \bar{v}K^+$) > 5.4 x 10 32 years at 90% C.L.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Room-temperature calorimeter for x-ray free-electron lasers

We have developed a room-temperature calorimeter for absolute radiant power measurements of x-ray free-electron lasers. This room-temperature calorimeter is an electrical substitution device based on the equivalence of electrical and radiant heating. Consequently, the measured radiant powers are traceable to electrical standards, i.e., the International System Units (SI). We demonstrated the performance of the room-temperature calorimeter by electrical power measurements (offline tests). In the offline tests, the room-temperature calorimeter was proven to be able to measure external powers up to at least 6.9 mW, which exceeds the upper limit (∼4 mW) of a cryogenic radiometer (the primary standard detector in Japan). In addition, measurement uncertainties of the room-temperature calorimeter were evaluated to be less than 1.0%, which is adequate for the radiant power measurements of x-ray free-electron lasers. An indirect comparison with the cryogenic radiometer was performed using a synchrotron radiation source to confirm the validity of the absolute radiant powers measured with the room-temperature calorimeter. The absolute radiant powers measured by the calorimeter agreed with those measured by the cryogenic radiometer within 0.6%, which is less than the relative standard uncertainty of the comparison (1.0%)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Results from KamLAND-Zen

KamLAND-Zen reports on a preliminary search for neutrinoless double-beta decay with 136 Xe based on 114.8 live-days after the purification of the xenon loaded liquid scintillator. In this data, the problematic 110m Ag background peak identified in previous searches is reduced by more than a factor of 10. By combining the KamLAND-Zen pre- and post-purification data, we obtain a preliminary lower limit on the 0νββ decay half-life of T 0ν 1/2 > 2.6×10 25 yr at 90% C.L. The search sensitivity will be enhanced with additional low background data after the purification. As a result, prospects for further improvements with future KamLAND-Zen upgrades are also presented.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Study of electron anti-neutrinos associated with gamma-ray bursts using KamLAND

We search for electron anti-neutrinos ( ν-bar {sub e}) from long- and short-duration gamma-ray bursts (GRBs) using data taken by the Kamioka Liquid Scintillator Anti-Neutrino Detector (KamLAND) from 2002 August to 2013 June. No statistically significant excess over the background level is found. We place the tightest upper limits on ν-bar {sub e} fluence from GRBs below 7 MeV and place first constraints on the relation between ν-bar {sub e} luminosity and effective temperature.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Electronic and magnetic properties of off-stoichiometric Co{sub 2}Mn{sub β}Si/MgO interfaces studied by x-ray magnetic circular dichroism

We have studied the electronic and magnetic states of Co and Mn atoms at the interface of the Co{sub 2}Mn{sub β}Si (CMS)/MgO (β = 0.69, 0.99, 1.15, and 1.29) magnetic tunnel junction (MTJ) by means of x-ray magnetic circular dichroism. In particular, the Mn composition (β) dependences of the Mn and Co magnetic moments were investigated. The experimental spin magnetic moments of Mn, m{sub spin}(Mn), derived from x-ray magnetic circular dichroism weakly decreased with increasing Mn composition β in going from Mn-deficient to Mn-rich CMS films. This behavior was explained by first-principles calculations based on the antisite-based site-specific formula unit (SSFU) composition model, which assumes the formation of only antisite defect, not vacancies, to accommodate off-stoichiometry. Furthermore, the experimental spin magnetic moments of Co, m{sub spin}(Co), also weakly decreased with increasing Mn composition. This behavior was consistently explained by the antisite-based SSFU model, in particular, by the decrease in the concentration of Co{sub Mn} antisites detrimental to the half-metallicity of CMS with increasing β. This finding is consistent with the higher tunnel magnetoresistance ratios which have been observed for CMS/MgO/CMS MTJs with Mn-rich CMS electrodes.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Beyond crystallography: Diffractive imaging using coherent x-ray light sources

X-ray crystallography has been central to the development of many fields of science over the past century. It has now matured to a point that as long as good-quality crystals are available, their atomic structure can be routinely determined in three dimensions. However, many samples in physics, chemistry, materials science, nanoscience, geology, and biology are noncrystalline, and thus their three-dimensional structures are not accessible by traditional x-ray crystallography. Overcoming this hurdle has required the development of new coherent imaging methods to harness new coherent x-ray light sources. Here we review the revolutionary advances that are transforming x-ray sources and imaging in the 21st century.

Miao, Jianwei↗
DOE OSTI2014

Light desorption from an yttrium neutralizer for Rb and Fr magneto-optical trap loading

We present here the first evidence of photodesorption induced by low-intensity non-resonant light from an yttrium thin foil, which works as a neutralizer for Rb and Fr ions beam. Neutral atoms are suddenly ejected from the metal surface in a pulsed regime upon illumination with a broadband flash light and then released in the free volume of a pyrex cells. Here atoms are captured by a Magneto-Optical Trap (MOT), which is effectively loaded by the photodesorption. Loading times of the order of the flash rise time are measured. Desorption is also obtained in the continuous regime, by exploiting CW visible illumination of the metallic neutralizer surface. We demonstrate that at lower CW light intensities vacuum conditions are not perturbed by the photodesorption and hence the MOT dynamics remains unaffected, while the trap population increases thanks to the incoming desorbed atoms flux. Even with the Y foil at room temperature and hence with no trapped atoms, upon visible illumination, the number of trapped atoms reaches 10{sup 5}. The experimental data are then analyzed by means of an analytical rate equation model, which allows the analysis of this phenomenon and its dynamics and allows the determination of critical experimental parameters and the test of the procedure in the framework of radioactive Francium trapping. In this view, together with an extensive investigation of the phenomenon with {sup 85}Rb, the first demonstration of the photodesorption-aided loading of a {sup 210}Fr MOT is shown.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Radioactive ion beam transportation for the fundamental symmetry study with laser-trapped atoms

The search for the violation of the fundamental symmetry in a radioactive atom is the promising candidate for precision tests of the standard model and its possible extensions. The subtle signal arising from the symmetry violation is enhanced in heavy atoms, such as a francium (Fr). To realize high precision measurements, a large amount of radioactive isotopes is required. The Fr is produced via a nuclear fusion reaction using a melted gold target with a {sup 18}O primary beam at Cyclotron and Radioisotope Center, Tohoku University. The maximum extraction efficiency of the Fr ion was achieved at approximately 35%. The beam line consists of an electrostatic deflector, three electrostatic quadrupole triplets to the measurement area at 10 m away from the reaction point, and several beam diagnosis systems. We optimized parameters of the beam line.

43 PARTICLE ACCELERATORS↗