Satoshi Kojima

Fission-fusion correlation by fission reactor irradiation with improved control

Abstract The necessity for the elimination of exposure to neutrons at lower temperatures during start-up and shut-down of the reactor is confirmed by experiments which compare the result of irradiation of metals with conventional and improved temperature control in JMTR. Only several percent of exposure to neutrons at lower temperatures is found to result in a one hundred percent difference of radiation induced microstructures in some cases. All differences can be understood from the microstructural development mechanisms, i.e. from the temperature dependence of the stability of point defect clusters and from the relationship of the transient temperature to the temperature for nucleation and growth. Fission neutron irradiation data with improved control are compared with fusion neutron irradiation data from RTNS-II. The differences of vacancy and interstitial clusters formed directly from cascades, observed in samples irradiated as thin foils, are understood when the difference in the primary recoil energy spectrum and the thermal stability of the clusters are taken into consideration. The defect structures which are developed and/or modified by the reactions of freely migrating point defects, such as vacancy clusters interstitial type dislocation structures and voids, observed in samples irradiated as bulk, are remarkably different in the two cases. Factors to be applied to the fission neutron irradiation dose to introduce microstructures equivalent to those by fusion neutrons are found to range widely, depending on the kind of microstructure, materials and irradiation temperature, from a value less than one up to 30 in the scaling of damage energy per atom.

An efficient functionalization of [60]fullerene. Diels-Alder reaction using 1,3-butadienes substituted with electron-withdrawing and electron-donating (silyloxy) groups

Abstract The Diels-Alder strategy was found suitable for the functionalization of C 60 using 1,3-butadienes substituted with an electron-withdrawing group as well as with an electron-donating group, giving cyclohexene-fused C 60 derivatives having ethoxycarbonyl, acetyl, cyano, phenylsulfonyl and nitro substituents. These cycloadducts were stabilized by conjugation with the substituent and no cycloreversion took place. Though the dienes are electron-deficient in nature, the HOMO (diene) - LUMO (C 60 ) interaction was significant as indicated by PM3 calculations.

Hetero-diels-alder reaction of fullerene: Synthesis of thiochroman-fused C60 with o-thioquinone methide and oxidation to its S-oxides

Cycloaddition reaction of C60 with o-thioquinone methide afforded a thiochroman-fused C60 derivative, using benzothiet as a precursor. The cycloadduct was further oxidized with mCPBA to the corresponding sulfoxide and sulfone. However, the self-sensitized photooxygenation to the sulfoxide was unsuccessful.

Criterion of subcascade formation in metals from atomic collision calculation

Abstract Atomic collision calculation of displacement cascades is performed, based on the binary collision approximation with systematically varied materials and energy of incident atom, to understand the break up process of a large cascade into subcascades. The mean distance between collisions to transfer a large kinetic energy to a target atom, and the size of the vacancy rich region produced by the target atom are compared as a function of the transferred energy to a target atom. The relation between these two parameters are proposed as a criterion of subcascade formation. When the criterion is applied to several metals, a tendency for larger subcascade energy for heavier atomic species is obtained. The origin of the formation of subcascade and factors which determine the subcascade parameters, such as subcascade energy and subcascade zone size are discussed.

Fission reactor irradiation of materials with improved control of neutron flux-temperature history

Abstract Eliminating the deficiency in the conventional temperature control, irradiation of materials with the Japan Material Testing Reactor is performed with an newly-designed in-core irradiation ring with which the sample temperature can be maintained regardless of the reactor power. The defect microstructures in various materials are compared with those introduced by irradiation with conventional control. The strong influence of the transient lower temperature irradiation during the start-up of the reactor is obvious for the samples irradiated with conventional control. The influence is fully understood from the temperature dependence of the microstructure evolution mechanism. The necessity of improved control is reconfirmed.

Diffraction contrast images of small stacking fault tetrahedra in f.c.c. metals

Abstract Transmission electron microscopy images of stacking fault tetrahedra (SFTs) are studied in detail both experimentally and by image simulation. Experimental dark-field diffraction contrast images of SFTs are examined under various conditions. The image contrast of stacking faults and stair-rod dislocations are simulated based on standard multi-beam dynamical theory, and the image contrast of very small SFTs (< 2.6 nm) is calculated by the multi-slice method. The correspondence between experimental and calculated results under systematically varied conditions is quite satisfactory. Stacking faults make a larger contribution to the total SFT image than stair-rod dislocations. The images are generally smaller than the SFT. The difference in size depends on many parameters such as deviation from the Bragg condition, location in the foil, and specimen thickness. However, the difference is always smaller than the fringe spacing in the stacking fault image, and is generally smaller at a larger deviation ...

Dihydrothiopyran-fused [60]fullerene from hetero-Diels–Alder reaction with thioacrylamide and acyl chloride

[60]Fullerene undergoes a smooth irreversible hetero-Diels–Alder reaction with an α,β-unsaturated thiocarbonyl compound, prepared in situ from thioacrylamide and acyl chloride, to give dihydrothiopyran-fused [60]fullerene cycloadducts.

δ-valerolactam derivative of C60 from hetero Diels-Alder reaction with 1,3-bis(tert-butyldimethylsiyloxy)-2-aza-1,3-butadiene

Abstract The title 2-aza-1,3-diene reacted smoothly with C60 at room temperature to give 2-piperidonefused C60 after hydrolysis A silyoxy group on the piperidone ring was replaced by alkoxy groups by acid-catalyzed substitution reaction with alcohols via an iminium cation intermediate. This type of reaction was applied to reduction by use of triethylsilane to give the parent δ-valerolactam derivative of C60.

Synthesis of Heterocycle-Containing [60]Fullerene Derivatives

Abstract Fullerene functionalization with heterocycles is reviewed, focusing attention on cycloaddition methodology and oxidative heterocyclization. 1 1This paper was presented before the Symposium 3 on ‘Expanded Horizons of Fullerene Science and Technology’ organized by L. Y. Chiang, E.Osawa, H. Terrones and M. Saunders at the 4th International Conference on Advanced Materials (ICAM-IV), Aug. 27 to Sept. 1, 1995, Cancun, Mexico.

Effect of cascade localization induced bias on defect structure evolution

Abstract A vacancy dominant atmosphere during neutron irradiation was analyzed with special attention on the initial local distribution of point defects in a cascade, i.e. a vacancy rich region which occupies a volume smaller that that occupied by interstitials. When the diffusion of vacancies starts from this localized volume and there are sinks in the cascade, vacancies have more possibilities to be absorbed by sinks than interstitials which start from an expanded volume. Consequently the contribution of vacancies in modifying the microstructure in the cascade is larger than that of interstitials. The model was applied to experimentally observed interstitial loop shrinkage and void swelling. The importance of the effect of the difference in initial local distributions of two species of point defects in the cascade (Cascade Localization Induced Bias) was emphasized.