Tsuneki Ichikawa

Possibility of Radiation-Induced Degradation of Concrete by Alkali-Silica Reaction of Aggregates

The effect of Ar ion irradiation on the reactivity of crystalline and amorphous quartz to alkali has been examined for clarifying whether radiation from nuclear reactors accelerates the degradation of concrete by inducing alkali-silica reaction of aggregates. Distorted amorphous quartz generated on the surface of quartz by irradiation of a 200 keV Ar ion beam is at least 700 times and 2.5 times more reactive to alkali than crystalline and regular amorphous quartz, respectively. The high reactivity of the distorted amorphous quartz indicates that the degradation of concrete by alkalsilica reaction is possible to be induced by nuclear radiation even the aggregates are inert to alkali before the irradiation. The critical radiation doses for the degradation of aggregates containing crystalline quartz are estimated to be 5 × 1019 n/cm2 for fast neutrons with energy >0.1 MeV, and 5×1011 Gy for beta and gamma rays. They are 1×1019 n/cm2 and 0.5tiems;1011 Gy, respectively for aggregates containing amorphous quartz.

Radical formation in the radiolysis of solid alanine by heavy ions

Abstract Radical formation in solid α-alanine irradiated with 175-MeV Ar8+ and 460-MeV Ar13+, 220-MeV C5+, and 350-MeV Ne8+ ions were studied by the ESR method. The radical yield (number of radicals per incident ion) is constant below the critical fluence of about 1010 ions cm−2 for the Ar ions, 1011 ions cm−2 for the C ion, and 5 × 1011ions cm−2 for the Ne ion. Above the critical fluence, the yield decreases with increasing ion fluence. G-value of the radical formation was obtained from the constant yield at the low fluences. The G-value is not a simple function of LET. This is ascribed to the difference in lateral dose distribution of ion tracks. Assuming a simple cylindrical shape of the ion tracks, the average dose in and the radius of the ion tracks were estimated from the G-values. The radius is 8–25 nm, which is larger than the radius of 2–5 nm for 0.5–3 MeV H+ and He+ ion-irradiations. The fluence-yield curves were simulated with the cylindrical tracks and with the dose-yield relationship for the radical formation in γ-irradiated alanine. The simulated curves agree well with the experimental ones. With the cylindrical model of ion tracks, the variation of the radical yield at the high fluences can be estimated for solid alanine irradiated with several hundreds of MeV heavy ions.

Relation between track structure and LET effect on free radical formation for ion beam-irradiated alanine dosimeter

The yield and local concentration of free radicals generated from alanine (α-aminopropionic acid) by irradiation with 3 MeV H+ and He+ ions were examined by means of electron spin resonance (ESR) and ESR power saturation methods at room temperature. The G-value of the radical formation showed a marked dependence on linear energy transfer (LET) of the ions. The G-value for the H+ ion (average LET: 28 eV/nm) was almost the same as that for γ-irradiation and it was smaller by a factor of 1/4.7 for the He+ ion (average LET: 225 eV/nm). Combining the local concentration of the free radicals along the ion tracks with the G-values and the reported ion range, the radius of a track filled with free radicals was estimated to be 4 ≈ 5 nm by assuming a simple rod-shaped track with a constant radius and homogeneous distribution of the free radicals in it. The track radius scarcely depends on the LET within the range examined. The radiation energy deposited in the core region of the ion track was concluded to spread over the rod to generate free radicals.

Electron spin echo studies of Cu2+ on silica surfaces: Interaction with water and ammonia adsorbates

An electron spin echo modulation study of cupric ion exchanged into silica gel by an ammonia complex shows that Cu2+ is coordinated to only two NH3 molecules. This coordination is reversible by thermal activation. Adsorption of H2O instead of NH3 also shows coordination to only two H2O molecules which is thermally reversible. From these electron spin echo results and electron spin resonance spectra, it is postulated that in the presence of adsorbate the cupric ion has a distorted octahedral environment involving coordination to two adsorbate molecules and four lattice oxygens.

A single crystal EPR study of ground state triplet trimethylenemethane

Trimethylenemethane, a ground state triplet, has been generated in a single crystal of methylenecyclopropane by γ irradiation at 77 K and studied by the electron paramagnetic resonance technique in the temperature range 4.2–106 K. From the observed anisotropy of the EPR spectra, the zero‐field splitting constants can be determined as D=0.0248 cm−1 and ‖E‖?0.0003 cm−1, and the principal values of the proton hyperfine coupling tensor as −14, −38, and −26 MHz with an isotropic coupling of −26 MHz at 77 K. Computer simulations of some of the spectra were performed using a computer program developed for this investigation. Both the position and the intensity of the spectral lines were reproduced with a good result. The simulations gave a positive sign for the zero‐field splitting constant D. The zero‐field splitting is temperature dependent above ca. 20 K, probably due to an oscillating motion of the molecular plane. The hyperfine structure changes above ca. 80 K and becomes isotropic at 100 K. This change is ...

Effect of Nuclear Radiation on Alkali-Silica Reaction of Concrete

The effect of electron beam-irradiation on the reactivity of plagioclase, one of the major minerals composing volcanic rocks, to alkali has been examined to clarify whether nuclear radiations accelerate the alkali-silica reaction of concrete containing volcanic rocks as aggregates. Irradiation of plagioclase with a 30 keV electron beam at a dose of more than 0:9 × 108 Gy converts a crystalline plagioclase to an amorphous one that is 35 times more reactive to alkali than the crystal. The high reactivity of the irradiated plagioclase indicates that the deterioration of concrete by alkali-silica reaction is possible to be induced by nuclear radiations even when the aggregates are inert to alkali before the irradiation.

Radical formation in the radiolysis of solid alanine by protons and helium ions

Abstract Radical formation in solid α-alanine irradiated with 0.5-, 1-, 2-, and 3-MeV H + , 0.5-, 1-, and 3-MeV He + ions were studied by means of electron spin resonance. The radical yield (number of radicals per incident ion) is constant below the critical fluence of about 10 12 ions cm −2 . Above the critical fluence, the yield decreases with increasing ion fluence. G -value of the radical formation was obtained from the constant yield at the low fluences. Assuming a simple cylindrical shape of the ion tracks, the average radii of the ion tracks were estimated from the G -values. The estimated value of the radius is from 2 nm to 5 nm. The dependence of the radical yield on the ion fluence was simulated with the cylindrical model of ion tracks and dose-yield relationship for γ-irradiation. The observed yield decreases more than the simulated one above the critical fluence. This difference is ascribed to higher damage on the solid alanine by the ion irradiation than by γ-irradiation.

Mechanism of radiation-induced degradation of poly(methyl methacrylate) — temperature effect

Abstract ESR and gel permeation chromatographic measurements of poly(methyl methacrylate) γ-irradiated between 77 and 300 K have been carried out to elucidate the mechanism of radiation-induced degradation of the polymer. It is revealed that the scission of the main chain does not take place immediately after the absorption of radiation energy but is induced by the intramolecular radical conversion of the side-chain COOĊH 2 radical to the tertiary CH 2 Ċ(CH 3 ) radical followed by the main-chain β-scission of the latter radical. The degradation scarcely takes place below 200 K, because the side-chain radical starts to convert above 200 K. The residual monomer in the polymer reacts with the side-chain radical below 200 K to generate the stable propagating-type radical, so that the degradation is suppressed even after warming the polymer to the ambient temperature.

Suppression of the Anderson localization of charge carriers on polysilane quantum wire

Abstract Comparison of the ESR and electronic absorption spectra of the radical ions of poly(cyclohexylmethylsilane) and poly(n-decyl-(s)-2-methylbutylsilane) has shown that the Anderson localization of charge carriers on part of the Si–Si polymer skeleton can be suppressed by replacing the pendant groups with bulky ones. Replacement reduces the flexibility of the polymer skeleton and therefore the dispersion of the resonance energies of the charge carriers between adjacent Si atoms, which suppresses the localization of the charge carriers arising from irregularity of the periodic potential field on the skeleton.

Nuclear modulation effect in electron spin echoes resulting from nuclear hyperfine and quadrupole interactions with a nucleus of an arbitrary spin

Approximate algebraic expressions for the nuclear modulation effect in electron spin echoes resulting from nuclear hyperfine and quadrupole interactions with a nucleus of an arbitrary spin are derived by using a third order perturbation method. The contribution of the quadrupole interaction on both the modulation amplitude and the modulation frequencies is included in the expressions. The validity of the expressions is examined by comparing the modulation spectra with exact ones obtained by the numerical calculation of the Hamiltonian for the spin echoes. It is shown that the expressions are applicable even for relatively short electron–nuclear distance and strong quadrupole interaction (r>0 and e2qQ/h<0.6 MHz for D nucleus).