Ken’ichi Kuge

The electronic structure of Cu + , Ag + , and Au + zeolites

A variety of procedures have been used to prepare d10-zeolite materials. The electronic structure of these materials can be regarded to a first approximation as a superposition of the framework, of the charge compensating ions, of solvent molecules and of guest species. Zeolite oxygen to d10-ion charge transfer transitions dominate the electronic spectra if the ions coordinate to the zeolite oxygens. Specific coordination sites can influence the energy and the intensity of these transitions remarkably. Intra guest transitions dominate in quantum dot materials, as discussed in detail for luminescent Ag2S zeolite A. The zeolite is not needed for the photocatalytic water oxidation on Ag+/AgCl photo anodes with visible light. It can, however, be used to increase the active surface area substantially.

Readout technologies for directional WIMP Dark Matter detection

The measurement of the direction of WIMP-induced nuclear recoils is a compelling but technologically challenging strategy to provide an unambiguous signature of the detection of Galactic dark matter. Most directional detectors aim to reconstruct the dark-matter-induced nuclear recoil tracks, either in gas or solid targets. The main challenge with directional detection is the need for high spatial resolution over large volumes, which puts strong requirements on the readout technologies. In this paper we review the various detector readout technologies used by directional detectors. In particular, we summarize the challenges, advantages and drawbacks of each approach, and discuss future prospects for these technologies.

Preparation of Gelatin Layer Film with Gold Clusters in Using Photographic Film

A gelatin layer film with gold clusters is produced by taking advantage of the photosensitivity of silver halide photography. Through exposure silver specks, which are called latent-image specks and are composed of several reduced silver atoms, are formed on the surface of silver halide grains in the photographic film. As the latent-image specks act as a catalyst for redox reaction, reduced gold atoms are deposited on the latent-image specks when the exposed film is immersed in a gold (I) thiocyanate complex solution for 5–20 days. Subsequently, when the silver halide grains are dissolved and removed, the gelatin layer film with gold clusters remains. The film produced by this method is purple and showed an absorption spectrum having a maximum of approximately 560 nm as a result of plasmon absorption. The clusters continued to grow with immersion time, and the growth rate increased as the concentration of the gold complex solution was increased. The cluster diameter changed from 20 nm to 100 nm. By this method, it is possible to produce a gelatin film of a large area with evenly dispersed gold clusters, and since it is produced only on the exposed area, pattern forming is also possible.

NEWS: Nuclear Emulsions for WIMP Search

Nowadays there is compelling evidence for the existence of dark matter in the Universe. A general consensus has been expressed on the need for a directional sensitive detector to confirm, with a complementary approach, the candidates found in conventional searches and to finally extend their sensitivity beyond the limit of neutrino-induced background. We propose here the use of a detector based on nuclear emulsions to measure the direction of WIMP-induced nuclear recoils. The production of nuclear emulsion films with nanometric grains is established. Several measurement campaigns have demonstrated the capability of detecting sub-micrometric tracks left by low energy ions in such emulsion films. Innovative analysis technologies with fully automated optical microscopes have made it possible to achieve the track reconstruction for path lengths down to one hundred nanometers and there are good prospects to further exceed this limit. The detector concept we propose foresees the use of a bulk of nuclear emulsion films surrounded by a shield from environmental radioactivity, to be placed on an equatorial telescope in order to cancel out the effect of the Earth rotation, thus keeping the detector at a fixed orientation toward the expected direction of galactic WIMPs. We report the schedule and cost estimate for a one-kilogram mass pilot experiment, aiming at delivering the first results on the time scale of six years.

Preparation of gold clusters in gelatin layer film using photographic film — 4: Effect of photographic materials

Abstract The effect of the properties of photographic materials on the preparation of gold clusters in a gelatin layer using a photographic film was examined. The cluster are formed by reducing a gold(I)–thiocyanate complex solution on latent image specks in emulsion grains. Gold clusters are marked as a non-linear optical material, and it was necessary for this purpose to condense the gold clusters in the layer. This was attempted by two methods. The first was to increase the emulsion grains in the layer, and the second was to increase the number of latent image specks on a grain. An ultrafine grain emulsion was applied for the former, while a high-intensity exposure and chemically sensitized emulsions were used to induce the dispersion of latent image specks for the latter. The characteristics of the clusters prepared from those emulsions were compared by absorption spectrum and size distribution. Both methods increased the plasmon absorption due to the gold clusters. The size of the clusters was similar, while absorbance increased with the sulphur-sensitization level. These results suggested that both were effective in condensing the gold clusters in the layer.

Dispersion of latent image specks on reduction-sensitized emulsions

Abstract The dispersion of latent image specks (LISs) on reduction-sensitized octahedral grain (Oct) and cubic grain (Cub) emulsions that were exposed to light of various intensity levels or to a radiation was studied. The number and distribution of LISs on a grain were determined with arrested development or gold deposition techniques. The sensitized Oct emulsions were sensitive to extra-low-intensity (24 or 48 h) exposure. This exposure displayed a narrow distribution with a one-speck-per-grain pattern. This changed to a broad distribution for 1 s exposure, which obeyed the Poisson distribution law at the highest sensitization level. These suggested that there were P centres present acting as precursors of LISs and inducing dispersion. The distribution for high-intensity (10−4 s) exposure obeyed the Poisson law for sensitized Oct and Cub emulsions. This dispersion of LISs occurred even in absence of the effective electron traps, when the supply rate of photoelectrons was high. The distribution of LISs was widely spread on exposure to α radiation, and the z and vb values were calculated, where z was the number of LISs formed when an a particle hit a grain once and vb was the number of LISs at which its linear increase with increasing number of striking a particles ceased and saturation began. Both z and vb increased with increasing sensitization level for the Oct emulsions, while they were almost constant for the Cub emulsions. These reflected the increase in or the absence of P centres. It was also suggested that the photolytic Ag3 speck is more effective than the Ag2 P centre as an electron trap.

Evaluation of noise limits to improve image processing in soft X-ray projection microscopy

Soft X-ray microscopy has been developed for high resolution imaging of hydrated biological specimens due to the availability of water window region. In particular, a projection type microscopy has advantages in wide viewing area, easy zooming function and easy extensibility to computed tomography (CT). The blur of projection image due to the Fresnel diffraction of X-rays, which eventually reduces spatial resolution, could be corrected by an iteration procedure, i.e., repetition of Fresnel and inverse Fresnel transformations. However, it was found that the correction is not enough to be effective for all images, especially for images with low contrast. In order to improve the effectiveness of image correction by computer processing, we in this study evaluated the influence of background noise in the iteration procedure through a simulation study. In the study, images of model specimen with known morphology were used as a substitute for the chromosome images, one of the targets of our microscope. Under the condition that artificial noise was distributed on the images randomly, we introduced two different parameters to evaluate noise effects according to each situation where the iteration procedure was not successful, and proposed an upper limit of the noise within which the effective iteration procedure for the chromosome images was possible. The study indicated that applying the new simulation and noise evaluation method was useful for image processing where background noises cannot be ignored compared with specimen images.

Effect of contrast enhancement prior to iteration procedure on image correction for soft x-ray projection microscopy

Soft X-ray microscopy is well recognized as a powerful tool of high-resolution imaging for hydrated biological specimens. Projection type of it has characteristics of easy zooming function, simple optical layout and so on. However the image is blurred by the diffraction of X-rays, leading the spatial resolution to be worse. In this study, the blurred images have been corrected by an iteration procedure, i.e., Fresnel and inverse Fresnel transformations repeated. This method was confirmed by earlier studies to be effective. Nevertheless it was not enough to some images showing too low contrast, especially at high magnification. In the present study, we tried a contrast enhancement method to make the diffraction fringes clearer prior to the iteration procedure. The method was effective to improve the images which were not successful by iteration procedure only.

Preparation of a hologram composed of a striped gold layer using photographic materials

We prepare a diffraction grating composed of the gold layer on a glass plate using the gold deposition development in photographic materials and following baking process. A high-resolution image with a spatial resolution of over 4000lines∕mm was obtained. A diffraction grating composed of gold particles in a gelatin layer was prepared by development in a gold-thiocyanate complex solution. The grating was then baked to burn out the gelatin layer and fuse the gold particles. The thickness of the grating composed of the gold layer was less than 10nm. After baking the grating had a bright gold luster and showed a clear higher-order diffraction on the reflecting side, while it showed only first-order diffraction before baking. The maximum efficiency of the first-order diffraction beam on the grating before baking was 8.8%. After baking, the maximum efficiency of the reflected diffraction beam was 1.6%. Using this method, it is possible to prepare stable holograms even in severe environments.

Colored tracks of heavy ion particles recorded on photographic color film

A new method to obtain the three-dimensional information on nuclear tracks was developed using color photography. Commercial color films were irradiated with ion beam and color-developed. The ion tracks were represented with color images in which different depths were indicated by different colors, and the three-dimensional information was obtained from color changes. Details of this method are reported, and advantages and limitations are discussed in comparison with a conventional method using a nuclear emulsion.