Makiko Muto

Observation of monochromatic and tunable hard X radiation from stratified Si single crystals

Abstract X radiation by 900 MeV electrons in accurately aligned 1–100 layers of 16 μm thick monocrystalline foils of Si was measured. We found intense and well collimated monochromatic photons, i.e. self-diffracted X rays (SDX), emitted to the “Bragg angle”. The intensity of SDX was much greater than the parametric X rays from a Si plate of equivalent thickness. For 35.5 keV X rays with 100 layered Si target, absolute brightness of SDX was comparable to the synchrotron radiation from a 1.7 GeV storage ring.

X-ray generation produced by relativistic electrons in compound “multifoil structure + crystal” targets

Abstract Novel concepts of X-ray production by relativistic electrons in stratified targets are developed. It is shown that by transmitting an electron beam through a compound target, consisting of a periodic multifoil structure and a crystal, it is possible to obtain the intense, tunable, quasi-monochromatic X-rays, emitting at large (Bragg) angles with respect to the electron beam axis due to the diffraction on the crystal of resonance transition radiation, previously generated in the multilayered structure. The first results of experimental investigation of this effect for 900 MeV electrons, transmitting through the periodic stack of 10 Mylar foils and pyrolytic graphite crystal, are presented. The obtained results show that, by using of the combined radiator, it is possible to produce much more intense X-rays than parametric X-ray radiation, emitting by relativistic electrons due to the diffraction of virtual photons of electron eigenfield during the electron passage through the crystal.

Cluster formation dynamics in a locally-confined gas layer mixed with the plume ablated by pulsed laser irradiation

Abstract The dynamical process of pulsed laser ablation is investigated by means of Monte Carlo simulations in order to develop a new cluster source. The interaction between the ablated Cu vapor plume and the He ambient gas induces strong shock compression of the gas by which the gas density is one order of magnitude increased and forms a stable gas layer mixed with the plume at the contact front. It is found that even with the target-wall distance as short as about 80 μm, a mixed layer more than 10 μm in thickness can be formed at about 15 μm away from the source wall. This layer can be locally-confined for a considerable long time of hundreds of ns. Frequent collisions occur among the atoms of vapor and gas within the confined layer which induce effective cluster aggregation. The thermodynamic state of this region is well defined, so that the mono-dispersed growth condition might form cluster beam with well-defined internal freedom.

Theory of nonlinear optical susceptibilities of antiferromagnetic Cr2O3

Abstract Not only the selection rules for the matrix elements but also the reality of their values matter to understand microscopically the nonreciprocal optical effects in antiferromagnetic crystals. We propose a microscopic model which can explain second-harmonic generation in Cr 2 O 3 by taking account of this circumstance.

Possible application of PXR to the beam-divergence measurements

Abstract The effect of the beam divergence on the parametric X-radiation has been experimentally investigated at NPI, Tomsk, and at INS, Tokyo for the electron energies 600 and 800 MeV, respectively. It has been shown that the crystal-orientation dependence of PXR is sensitive to the beam divergence, suggesting that PXR can offer a simple means for determining the angular divergence of high energy charged particle beams.

New polarimeter for high energy gamma-rays

Abstract A new type of polarimeter for gamma-rays of over a hundred MeV was built. It is based on a principle in which the polarization is obtained from the azimuthal angular distribution of recoil electrons in electron-positron pair productions in the Coulomb fields of electrons.

Prefrontal activations predict future performance improvement in learning phonics rules of English orthography and phonology

Effects of regularity, familiarity, and congruity of stimuli were investigated on Auditory and Visually Evoked Magnetic Fields. Regularity was controlled by exponent n on a fluctuation of 1/fn, Familiarity was controlled by the score of word familiarity in a database of Lexical Properties of Japanese. Congruity was controlled by the semantic distance of the components of the constructed stimulus. Decrement of these three factors of stimuli enhanced the amplitude and prolonged the latency of the AEF activity of the N100m component of primary auditory aria. The increment of the three factors of visual stimuli enhanced the VEF of the 150 ms and 220 ms components. The three factors of stimuli play similar roles for activity enhancement of the auditory and visual cortex, and provoked expectation of auditory stimuli and figure ground segmentation for visual stimuli. The activities of the cortex reflected the basic function of the conventionalization of the pattern of a repetitive experience unit in the process of the emergence of linguistic structure.

Nonreciprocal optical responses of antiferromagnetic Cr2O3

We will present a microscopic model to understand the nonreciprocal optical responses, i.e., the second-harmonic generation through electric and magnetic dipole moments and the magneto-electric effects. Here the twist crystalline field, which reflects the real crystal structure, is found to play an important role in both channels of the second-harmonic generation. Then we can explain the spectra of the second-harmonic generation through electric and magnetic dipoles. Absolute as well as relative magnitudes of the second-order susceptibilities through both channels are also estimated to be reasonable. In terms of the same model, we can also understand the magneto-electric spectra, i.e., the electric- and magnetic-dipole interference in the linear response.