Shuichi Okuda

A novel collagen hydrogel cross-linked by gamma-ray irradiation in acidic pH conditions

We made a new type of collagen gel by γ-ray irradiation of an acidic solution of type-I collagen, and performed comparative studies on a conventional gel and the new type of gel. The neutral gel, a conventional 0.3% (w/v) collagen gel, was formed at neutral pH and then irradiated by γ-rays. The acidic gel, a 0.3% (w/v) collagen gel, was formed directly from the acidic solution of collagen by γ-ray irradiation. Both types of gel were prepared, swollen in water and then dried for the measurement of specific water content. The neutral gel showed a relatively high specific water content and shrunk moderately, depending on the dose, while the acidic gel showed lower specific water content and shrunk clearly by γ-ray irradiation. A three-dimensional tangled network of microfibrils was clearly observed in the neutral gels by scanning electron microscopy, but not in the acidic gels. From these results, we concluded that the acidic gel was quite different from a conventional collagen gel. Sodium dodecylsulfate-polyacrylamide gel electrophoresis showed that the α 1 subunit and α 2 subunit of the collagen molecule were cross-linked. The triple-helical structure of collagen was only partially perturbed, but not denatured completely, because the circular dichroism spectrum of the collagen solution irradiated at 1.3 kGy was similar to that of native collagen solution. Amino-acid analysis revealed that tyrosine, phenylalanine and histidine decreased by irradiation in the neutral gel. In the case of the acidic gel, these three amino acids and methionine decreased. We considered that these amino acids were cross-linking points between the collagen subunits during the γ-ray irradiation.

Gelatin hydrogels cross-linked by γ-ray irradiation : materials for absorption and release of dye

Gelatin hydrogels cross-linked by γ-ray irradiation using 60Co as γ-ray source were prepared. As a model of controlled release of low-molecular-weight compounds, absorption and release of methylene blue, a water-soluble cationic dye, was investigated. Irradiated gelatin hydrogels did not redissolve at temperatures over 40°C, while unirradiated gels were thermoplastic and reversibly changed the stage between gel and sol. Measurement of both the wet weight after swelling in distilled water and dry weight after freeze-drying showed that the higher-dose irradiation gave stiffer and more compact gels with the lower specific water content, irrespective of the absorbed dose rate. The time-course of absorption and release of methylene blue in aqueous solution was measured. Since absorption of dye into gelatin gels was much affected by liquid phase pH, amount of absorption was higher in pH above an IEP of gelatins. Moreover, the absorption and release of methylene blue with Type-B gelatin were higher than with Type-A gelatin, respectively. Therefore, absorption and release of the dye depend on the electrostatic interaction between the dye molecule and gelatin.

Hydrogen gas evolution from water dispersing nanoparticles irradiated with gamma-ray

Hydrogen gas evolution from water dispersing nanoparticles under 60Co γ-ray irradiation was investigated under various conditions. Dispersion of TiO2, A12O3, ZnO, ZrO2 and CeO2 nanoparticles with average sizes of 6 nm - 11 µm showed hydrogen yields much higher than that obtained by pure water radiolysis, and the yields seemed to depend on their particle size and shape rather than their chemical species. Hydrogen yield increased with increasing γ-dose but not linearly, which implies the occurrence of a kind of reversing reaction. Some of the nanoparticles supported with Pt, Au and Pd were also examined. The yields were strongly affected by these noble metals, which indicates an important role of the particle surface in the total mechanism of the present hydrogen evolution.

Plasma application for detoxification of Jatropha phorbol esters

Atmospheric pressure non-thermal dielectric barrier discharge (DBD) plasma generated by helium gas at high voltage and input power of about 50 W was first applied to detoxification of Jatropha curcas phorbol esters (J. PEs) as well as standard phorbol ester (4β-12-O-tetradecanoyl phorbol-13-acetate, TPA) in water and methanol. Plasma irradiation on the solution sample was conducted for 15 min. In aqueous solution, only 16% of TPA was degraded and complete degradation of J. PEs was observed. On the contrary, complete degradation of both TPA and J. PEs in methanol was achieved by the same plasma irradiation condition. Hydroxyl radical (•OH) generated by plasma irradiation of the solution is expected as the main radical inducing the degradation of PEs.

Tritium depth profiling in surface regions of solids by use of the T(d, α)n reaction

Abstract Tritium depth profiling with an incident deuteron beam by use of the T(d, α)n reaction was studied for the case where the energy spectrum of the emitted α-particles is used to evaluate the depth profile. Appropriate probing energies were considered to be from 100 keV to 1 MeV. The characteristics of this method were evaluated for a variety of experimental measurement conditions. The method was demonstrated for thin titanium layers containing tritium at probing energies of about 600 keV. The distribution of tritium obtained were almost uniform with depth, as expected, and the measured tritium content agreed well with that nominally stated.

Depth profiling of tritium in solids with the nuclear reaction induced by deuteron bombardment

A method for the measurement of depth profiles of tritium in solids has been developed in which the 3H(d,n)4He reaction is used. This method is nondestructive with relatively high depth resolution in the surface region of the solids. The validity of the present method has been supported by the examination of the depth profile measured for a tritium target as is used for a neutron source.

Depth profiling of tritium in a thin titanium layer bombarded with deuterium ions

Abstract Depth profiles of tritium in a thin titanium layer were measured using the T(d, α)n reaction. A new sample showed a nearly rectangular profile of tritium with concentrations from 1.1 to 1.2 atomic ratios (T/Ti). After the bombardment of 360 or 570 keV D 3 + ions at 20 ° C a dip was formed on the profile about the projected range of the incident ions, which indicates that tritium atoms and deuterium atoms were mixed at the implanted sites and then diffused. At a high dose rate of about 16 μA/cm 2 two dips were observable on the profile, in which a peak was formed about the projected range. For a temperature of −110 ° C the profile showed almost no change after a bombardment and the succeeding annealing at room temperature for 20 h. These results are discussed on the basis of the previous results.

Formation of Large Blisters on Rolled Mo Surface Bombarded with Hydrogen Ions

Relatively large blisters were observed on the surface of rolled plates of polycrystalline molybdenum bombarded with hydrogen ions at energies of 160 eV or greater. Some blisters have a skin thickness about 2 orders of magnitude larger than the projected range of implanted ions, thus being distinguished from those of usual radiation blistering. The formation of such large blisters depends on the texture of the metal specimen, and may be attributed to the high pressure gas produced by the recombination of hydrogen atoms at the site of the defects originating in the fabrication of the specimen.

Depth Profiles of Implanted H and He in Metal Mo Determined with Backscattered Protons

The depth profiles of the atoms trapped in polycrystalline molybdenum after implantation of 12-keV H3+ to a dose of 0.95 C/cm2 at 440 K and 780 K, and of 2-keV He+ to 0.19 C/cm2 at 300 K, have been determined by measuring the energy spectra of backscattered protons with an incident energy of 40 keV. The ratio of the number density of trapped atoms to that of metal atoms reaches about 0.5 in each case. The major difference between the results for H and He is that the depth profile of implanted hydrogen has a peak at a depth slightly less than the projected H-ion range, while that of implanted helium peaks at a depth about 3 times longer than the projected He-ion range.

Depth profiling study on the migration of tritium in titanium induced by deuterium-ion bombardment

Abstract A thin titanium layer with uniformly absorbed tritium (T/Ti ~1.0) was bombarded by 390 keV D 3 + ions (130 keV per deuteron). Bombardment was performed at low (111 K) and room temperatures up to fluences of 5.9 × 10 18 D / cm 2 and 3.0 × 10 18 D / cm 2 , respectively. Depth profiles of tritium up to a depth of 0.8 mg/cm 2 (~1.8 μm) were measured and the change of the profile with fluence was investigated by means of the T(d, α)n nuclear reaction. At both of the temperatures, a dip was formed on the depth profile of tritium at the depth around the projected range, indicating that the deuteron bombardment induced the migration of tritium against the concentration gradient. At the low temperature, the dip showed a gradual growth with fluence and saturation of the growth at the higher fluences, which could not be described by the existing model for isotope mixing. The spectrum of protons from the D(d, p)T reaction obtained in the same measurement suggested that the release of deuterium suddenly started at the final stage of the present bombardment. The dip formed at room temperature was larger than that at the low temperature. The migration of tritium induced by the bombardment is discussed on the basis of the experimental results obtained.