Keiichi Ohno

Application of ESR imaging to a continuous flow method for study on kinetics of short-lived radicals

Abstract Spatial distribution of ascorbic acid free radicals in a flat cell of a continuous flow apparatus was observed by an ESR imaging method with a magnetic field gradient of 3.5 G · cm −1 along the solution flow direction. The novel method served to measure the rapid decay reaction, the half-life period of which was 1.4 milliseconds.

ESR imaging investigation on depth profiles of radicals in organic solid dosimetry

Abstract ESR imaging was applied to the measurement of radical depth profiles generated in organic solid dosimeters. Alanine/paraffin, alanine/polystyrene and sucrose/paraffin mixtures were irradiated with the electrons from the 4-MeV Linac. The theoretical energy-deposition distributions were calculated by using an algorithm derived by Tabata and Ito. Experimental radical depth profiles agree well with theoretical energy-deposition distribution. In spite of the existence of some problems, and the need to improve e.g. the occurrence of the artifact, the capability of depth-profile dosimetry using ESR imaging was shown. The radical-depth profiles in polypropylene-containing hindered amine light stabilizers, suggested the significance of depth-profile measurements in composite materials irradiated with high linear-energy-transfer radiations.

Computer Recording in Rapid Scan ESR Spectroscopy

SUMMARY Rapid scanning [1, 2] in ESR spectroscopy is one of the methods by which one can obtain significant information relating to rapid chemical reactions occurring in several milliseconds. One of the advantages of this rapid scanning method is the ability to investigate phenomena occurring rapidly and singly, such as a decay of electrons trapped in a solid matrix. This note reports on the coupling of an electronic computer (JEOL JEC-5) with the rapid scan unit in order to record ESR spectra with high signal-to-noise ratio in several milli-seconds, and also on the successful application of this technique to the study of chemical reactions. This use of the computer is neither as a computer of average transients (CAT) [3, 5] nor as a sampling method for the detection and display of rapidly changing spectra [6, 7]. The apparatus used in this experiment consists of an ESR spectrometer, a Helmholtz coil, a power amplifier, a sawtooth wave generator, a trigger pulse generator, and an electronic computer. A bl...

IN-PILE CALORIMETRIC DOSIMETRY. I.

An adiabatic calorimeter has been designed for measuring energy absorbed in materials (C, Al, (CH2)n and Pb) placed in the experimental hole of a nuclear reactor.Details are given of the apparatus and procedures of the calorimeter, followed by an account of the results of calibration and of dosimetry in the TRIGA II type reactor of the Atomic Energy Research Laboratory of the Musashi Institute of Technology, The operating temperatures were 25 ?? -30 ?? at 100kW reactor power, and the energy deposition (or dose) rate was 0.2-2mW/g. The performance has been satisfactory in spite of the poor agreement between the observed and calculated rates of temperature rise. The ratio between energy absorption due to fast neutron scattering and that due to γ-rays obtained in the TRIGA II is consistent with the data obtained with BEPO. The experimental accuracy (standard error) at full reactor power is estimated to be within 2.1%.

Analysis of magnetic-field-induced distribution using ESR parallel-edge lines of a slow tumbling spin probe in a rigid liquid crystal

Abstract The ESR spectra of a slowly tumbling nitroxide radical in rigid p,p-methoxy benzylidene n-butylaniline (MBBA) exhibit three step-shoulders at resonant magnetic fields of the molecules with the symmetric axes oriented nearly parallel to the applied static magnetic field. The linewidth differences in two parallel-edge fines for hyperfine components in the second derivative spectra were observed and analyzed as the sum of a term dependent on rotational correlation time and a term which contains the effects of magnetic field Bq quenching the samples at 77 K and the degree of orientation distribution. The first term has been predicted by Kivelson and Lee to vary as τ c −1 2 at a limit of τc → ∞, where τc is the rotational correlation time. The second term was determined to be inversely proportional to 1 θ 0 2 + ΔχB q 2 /2kT eq ) 2 where θ0/√2 means the standard deviation from the mean of the Gaussian distribution, Δχ (=X| − χ⊥) is the anisotropy in diamagnetic susceptibility, and Teq is the temperature of liquid crystal before quenching.