Performance of compact pulse radiolysis system using a photocathode RF gun

A compact pulse radiolysis system using a photocathode RF gun was installed at Sumitomo Heavy Industries. Some performance tests were conducted concerning the electron beam and the laser pulse. The energy and the per-pulse charge of the electron beam were measured to be 1.75 MeV max. and 1 nC. The fluctuation of the charge was restricted within 2%. The pulse widths of the electron pulse and the analyzing laser pulse were 20 ps and 15 ps, respectively. The timing jitter between electron pulse and the laser pulse was ±5.7 ps. Based on these measurements, the all-over time resolution can deduced to be about 25 ps.     

Effect of oxidation dynamics on the film characteristics of Ce:YIG thin films deposited by pulsed-laser deposition

Thin films with different compositions of Ce-substituted yttrium iron garnet (Ce:YIG (Y₂CeFe₅O₁₂)), Ga-doped Ce:YIG (Ce:Ga:YIG (Y₂CeFe_4.25Ga_0.75O₁₂)), and Gd-doped Ce:YIG (Ce:Gd:YIG (Y_1.6CeGd_0.4Fe₅O₁₂)) were deposited on gadolinium gallium garnet (GGG (Gd₃Ga₅O₁₂)) substrates in O₂ or Ar background gas by pulsed-laser deposition (PLD) technique. Crystalline films were obtained at a lower O₂ gas pressure of 20 mTorr or at higher Ar gas pressures of more than 100 mTorr. In addition, the behavior of YO molecules was visualized by two-dimensional laser-induced fluorescence (2D-LIF), in order to investigate the oxidation dynamics in the ablation plume. The oxidation dynamics and the crystallinity had close correlation.     

Multi-reflection time-of-flight mass spectrograph for short-lived radioactive ions

RIKEN’s new RI-Beam Factory (RIBF) will provide unprecedented access to neutron-rich nuclei of importance to r-process nucleosynthesis. We are constructing an advanced multi-reflection time-of-flight mass spectrograph to perform precision mass measurements of these nuclei. We discuss the device and compare its performance to that of the well-known Penning trap mass spectrometer.     

Condensation of uranium hexafluoride in supersonic Laval nozzle flow

6 carried in a mixture of argon and methane was studied experimentally in a continuously operating supersonic Laval nozzle. The onset of condensation was detected by Rayleigh light scattering. Measurements of static pressure in the nozzle, together with the equations of isentropic flow, permitted the determination of the relation between the pressure of UF₆, P_k, and the temperature, T_c, at the observed onset of condensation. The experiments addressed conditions of condensation onset in the range 80<T_c<160 K and 0.1<P_k<3.0 Torr. We found that there was no influence of the pressure of the carrier gas argon, which ranged from 3.5 to 68 Torr at onset points, on the onset of condensation. The dependence of the supersaturation ratio on temperature at the onset could be expressed by a straight line as deduced by P.P. Wegener and B.J.C. Wu from the classical theory of homogeneous nucleation [Adv. Colloid Interface Sci. 7, 325 (1977)]. These results indicate that supersonic expansion in the nozzle formed single-component droplets of UF₆ in a mixture of UF₆, CH₄, and Ar under the experimental conditions studied herein. Received: 23 December 1997 / Revised version: 7 April 1998     

Prediction of peptide retention times in normal-phase liquid chromatography with only a single gradient run.

Previous studies of peptide separation by normal-phase liquid chromatography have shown a linear relationship between the logarithm of the capacity factor and the logarithm of the volume fraction of modifier in the mobile phase. This permitted the use of a model to predict isocratic and gradient retention times based on data obtained by two initial gradient runs. In the present study, chromatographic behavior of 25 peptides in normal-phase liquid chromatography with isocratic elution have been studied and a linear relationship between the slope (S) and intercept [log k(0)] was obtained. This relationship was combined with the algorithm of prediction reported in the previous paper. The prediction of peptide retention times with only a single experimental gradient retention data was investigated.     

Tacticity, molecular weight, and molecular-weight-distribution relationships in stereoregular polyacrylonitrile prepared by electron beam irradiation canal polymerization

The preparation and characterization of stereoregular isotactic polyacrylonitrile (PAN) by electron beam (EB) irradiation on a urea canal complex are described. The EB method has several advantages over the ordinary γ-ray irradiation method: a very short polymerization time is needed (within a few seconds) and EB irradiation is carried out intermittently, and so all the polymer properties can be studied as a function of the EB irradiation dose. The structure–properties relationships of PAN, such as intrinsic viscosity versus the number-average molecular weight and the viscosity versus the isotacticity range were clarified. Significant information for the optimization of the tacticity of PAN was extracted. Received: 23 August 1999 Accepted : 10 January 2000     

Structures of 18-Crown-6 Complexes with Alkali Cations in Methanolic Solution as Studied by X-ray Absorption Fine Structure

The structures of 18-crown-6 (18C6) complexes with K⁺ and Rb⁺ in methanolic solutions have been studied by X-ray absorption fine structure (XAFS) at the Br K-edge as well as at the K and Rb K-edges. The XAFS spectrum at the K or Rb K-edge has indicated that either Br⁻ or solvent (methanol) molecules are present in the first coordination shell of K⁺ or Rb⁺ complexed by 18C6. However, the spectra obtained at the Br-K edge have strongly suggested that the alkali cations do not exist in the vicinity of Br⁻, indicating that no direct ion-pairing occurs between the 18C6 complex and Br⁻. The 18C6-K⁺ complex maintains D _3d symmetry even in methanol, and two methanol molecules coordinate the cation possibly from above and below the crown plane. In contrast, the corresponding Rb⁺ complex possibly forms an umbrella-shaped complex, in which Rb⁺ is situated slightly off the crown plane and three solvent molecules bind With the cation.     

Effect of Scattering on Spectral Imaging of Exposed Cortical Tissue for Brain Function Measurement

Optical imaging of an exposed cortex for brain function measurement is an attractive method for both clinical and physiological investigations. Spectral imaging of the exposed cortical tissue enables measurement of the activity-dependent changes in oxy- and deoxy-haemoglobin independently. Since the diffusely reflected light from the exposed cortex is highly scattered in the cortical tissue, the wavelength dependence of the optical properties of the tissue is likely to affect the images of oxy- and deoxy-haemoglobin changes obtained from the spectral images. In this study, the spectral images of the model of exposed cortical tissue are calculated by Monte Carlo simulation to investigate the influence of blurring by tissue scattering on the brain function measurement by the imaging. The images of the change in oxy- and deoxy-haemoglobin obtained from the spectral images at near infrared wavelengths are broadened and blurred due to the scattering in the cortical tissue. The influence of cross talk is more significant in the image calculated from the spectral images at the visible wavelengths. Inappropriate choice of the spectral range of images might increase cross talk and error in the images of oxy- and deoxy-haemoglobin changes.