G. Izawa

Mechanical property and dislocation dynamics of GaAsP alloy semiconductor

The mechanical behavior of GaAsP alloy semiconductor was investigated by means of compressive deformation and compared with those of GaAs and GaP. The nature of collective motion of dislocations during deformation was determined by strain-rate cycling tests. The dynamic characteristics of dislocations in GaAsP were found to be similar to those in elemental and compound semiconductors such as Si, Ge, GaAs, and GaP. An alloy semiconductor has a component of the flow stress that is temperature-insensitive and is absent in compound semiconductors.

A new internal standard method coupled with the standard addition method for proton-induced X-ray emission analysis and its application determination of Cu, Zn, Rb and Sr in biological materials

A new internal standard method coupled with the standard addition method for PIXE analysis has been developed. In its basic principle, this method is characterized by that a suitable element present initially in the sample is used as an internal standard, and further the comparative standard is prepared by applying the standard addition method to the duplicated sample. When a sample contains Wa g of trace element A to be determined together with an element B which is usable as an internal standard, and when the comparative standard is prepared by adding an exactly known amount of element A, Wa* g, to the duplicated sample, the absolute concentration of Wa can easily be determined by the following equation even if the above sample and comparative standard are irradiated separately by a different number of protons Wa=Wa*/[(R*/R)-1] where R and R* are ratios of net photopeak counts due to the characteristic X-rays from the element A and B in the irradiated sample and comparative standard, respectively. The usefulness of the method was examined through determination of Cu, Zn, Rb and Sr in two biological materials, such as spinach and orchard leaves. As a result, this method was demonstrated to be sensitive, highly reproducible and reasonably accurate.

Rapid and high-yield synthesis of carrier-free 18F-labelled alkyl flourides

Abstract A convenient method for the rapid and high-yield synthesis of carrier-free 18F-labelled alkyl fluorides was developed. The method involves (1) preparation of carrier-free 18F-labelled silver fluoride on surface-oxidized silver wool as a fluorinating source for 18F-labelling; and (2) synthesis of carrier-free 18F-labelled alkyl fluoride by connecting the above source to a radio-gas chromatograph, followed by ordinary gas chromotographic procedure. In the present method, the carrier-free 18F-labelled alkyl fluorides are synthesized by means of nucleophilic substitution reaction in the heterogenous gas-phase system. In order to examine the usefulness of the present method, syntheses of 12 carrier-free 18F-labelled alkyl fluorides were tested using the corresponding bromo- and iodo-compounds as the reactants. Synthesis and isolation of the labelled product in each case were sufficiently rapid and efficient to allow production of usable amounts of the desired compound.

Radio-liquid chromatogrphy for tritium labelled organic compounds using CaF2/Eu/ scintillator

The radio-liquid chromatography for the tritium labelled compoounds was constructed with a CaF2/Eu/ scintillator and applied successfully to analyze the products of recoil tritium reactions with trans-stilbene. The detection efficiency of tritium of 0.8% and the lowest detectable activity of 60 nCi were obtained for a 100–150 mesh CaF2/Eu/ scintillator.

Reactions of Recoil Tritium with Naphthalene and Its Derivatives in Solid Phase

Recoil reactions of tritium produced by 3 He (η, ρ) H in a gas phase with naphthalene and its derivatives (all solids) were investigated. It was found that intramolecular distribution of tritium was not uniform, in contrast to most of the experiments on aromatic compounds performed in the past. The non-uniformity was remarkable in strongly activated rings, and this was attributed to the ease of formation of an intermediate complex which decays to the parent type molecule tagged with tritium. The energy range of formation of the complex is supposed to be high enough to show no temperature dependence on the yield but low enough to display orientation effects in substitution reaction of hydrogen of the ring. The yields for tritium-labeled labile groups (OT and COOT) were investigated in the parent compounds. The trend of the yields could be correlated to the ring activity of aromatic compounds. An extraordinarily high yield was obtained for 1-hydroxy2-naphthoic acid, which has intramolecular hydrogen bonding. Thermal processes may be involved in the yields of labile tritium because of their temperature dependence.

ACOUSTIC EMISSION INDUCED BY TRITIUM DECAY

An observation of signals of acoustic emission induced by tritium decay is reported. The equipment consisting of PZT detectors, preamplifiers, low-cut filters and computer evaluation was used in this study as a differential system. The result shows that the two types of clear signals of acoustic emission are induced by tritium decay. They seem to be related to some radiation effects due to tritium irradiation, and not to acoustic waves during tritium decay events.

Tritium Exchange Reactions in Imidazole in Aqueous and Organic Solutions

Tritium exchange reactions were studied in aqueous and organic solutions of imidazole and methylimidazole. For the exchange in an aqueous solution the mechanism through ylide intermediate formation postulated by VAUGHAN et al. was modified in this study. The rate constant obtained by MASLOVA et al. was found to be too small compared to ours. For the exchange reaction of methylimidazole in an aqueous solution the rate decreased due to the effect of a methyl group attached to the aromatic ring. The C-2 tritiation of imidazole was studied in chloroform, acetone and dioxane for the first time. It was dependent on polymer properties. An intramolecular exchange mechanism was applicable to the trimer while an intermolecular exchange mechanism was applicable to the dimer. The rate constants of the exchange reactions in organic solutions were obtained for both mechanisms.

Application of proton induced X-ray emission to the qualitative and quantitative analysis of iodine in biological samples

Particle-induced X-ray emission (PIXE) was applied to evaluate the loss of volatile elements such as iodine in biological samples. The analytical quality of the method is comparable or better than spectrophotometry, which is currently believed to be the most reliable for iodine determination. The temperature dependence of volatility loss of trace iodine was characteristic, and the feature was divided into three temperature regions. The first one, ranging from room temperature to 200 °C, showed only a slight loss below 20% on drying; the second stage, between 200 °C and 350 °C, where carbonizing processes became prominent, showed a remarkable loss up to 50%; the last one, beyond 350 °C, was accompanied by a considerable loss of iodine (more than 80%) with ashing. Even in the analysis using low temperature ashing with oxygen plasma, the loss of iodine observed was considerable (nearly 80%). The significance of these findings by PIXE in trace analysis is noted to improve analytical quality of volatile elements, such as iodine in biological, medical and also environmental fields.

Annual variation of stable iodine in brown sea algae (hijiki, Hizikia fusiforme)

Abstract The amount of radioecologically significant iodine in sea algae was determined during the period from June 1982 to May 1983, applying the PIXE method. Parallel analyses were carried out on aliquot samples by two PIXE systems one at Tohoku University and one at NIRS. The results of the two systems for the corresponding samples were reasonably analogous. The annual mean value was 190 ppm in dry matter. The pattern suggested that the content of stable iodine changed periodically, showing three maxima: in September, March and May. The highest value was found in March (430 ppm in dry matter), whereas the lowest was found in December (95 ppm), the variation factor being nearly 4.5 in magnitude. This variation was not caused by the change of tide and currents in the environment nor by the physiological activities of the algae under natural conditions, but rather by the effect of harvestings for commercial foods. This detailed information on stable iodine can possibly provide the amount of its radioisotopes. which, as is currently expected in the field of radioecology, is necessary for a more precise evaluation of radiation doses.

Chemical effects on Lγ1/Lβ1 X-ray intensity ratio of molybdenum compounds

Chemical effects on the intensity ratio of LX-ray of molybdenum compounds irradiated by 11-keV electrons and by 3-MeV protons were studied using an X-ray crystal spectrometer. It was found that the intensity ratios of Lγ1/Lβ1 markedly decrease with increase of ionicity of molybdenum compounds. An exception was for the case of metallic molybdenum.