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This study aimed to develop a new method to quantitatively analyze body shape changes in patients during radiotherapy without additional radiation exposure using an optical surface tracking system. This method's accuracy was evaluated using a cubic phantom with a known shift. Surface images of three-dimensionally printed phantoms, which simulated the head and neck shapes of real patients before and after treatment, were used to create a deformation surface area histogram. The near-maximum deformation value covering an area of 2 cm

We compared predictive performance between dose volume histogram (DVH) parameter addition and deformable image registration (DIR) addition for gastrointestinal (GI) toxicity in cervical cancer patients. A total of 59 patients receiving brachytherapy and external beam radiotherapy were analyzed retrospectively. The accumulative dose was calculated by three methods: conventional DVH parameter addition, full DIR addition and partial DIR addition. \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}${D}_{2{cm}^3}$\end{document}, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}${D}_{1{cm}^3}$\end{document} and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}${D}_{0.1{cm}^3}$\end{document} (minimum doses to the most exposed 2 cm3, 1cm3 and 0.1 cm3 of tissue, respectively) of the rectum and sigmoid were calculated by each method. V50, V60 and V70 Gy (volume irradiated over 50, 60 and 70 Gy, respectively) were calculated in full DIR addition. The DVH parameters were compared between toxicity (≥grade1) and non-toxicity groups. The area under the curve (AUC) of the receiver operating characteristic (ROC) curves were compared to evaluate the predictive performance of each method. The differences between toxicity and non-toxicity groups in \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}${D}_{2{cm}^3}$\end{document} were 0.2, 5.7 and 3.1 Gy for the DVH parameter addition, full DIR addition and partial DIR addition, respectively. The AUCs of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}${D}_{2{cm}^3}$\end{document} were 0.51, 0.67 and 0.57 for DVH parameter addition, full DIR addition and partial DIR addition, respectively. In full DIR addition, the difference in dose between toxicity and non-toxicity was the largest and AUC was the highest. AUCs of V50, V60 and V70 Gy were 0.51, 0.63 and 0.62, respectively, and V60 and V70 were high values close to the value of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}${D}_{2{cm}^3}$\end{document} of the full DIR addition. Our results suggested that the full DIR addition may have the potential to predict toxicity more accurately than the conventional DVH parameter addition, and that it could be more effective to accumulate to all pelvic irradiation by DIR.

Functional lung avoidance during radiotherapy can help reduce pulmonary toxicity. This study assessed the potential impact of four-dimensional computed tomography (4DCT)-ventilation imaging-guided proton radiotherapy (PT) on stereotactic body radiotherapy (SBRT) by comparing it with three-dimensional conformal radiotherapy (3D-CRT) and volumetric modulated arc therapy (VMAT), which employ photon beams. Thirteen lung cancer patients who received SBRT with 3D-CRT were included in the study. 4DCT ventilation was calculated using the patients’ 4DCT data, deformable image registration, and a density-change-based algorithm. Three functional treatment plans sparing the functional lung regions were developed for each patient using 3D-CRT, VMAT, and PT. The prescribed doses and dose constraints were based on the Radiation Therapy Oncology Group 0618 protocol. We evaluated the region of interest (ROI) and functional map-based dose-function metrics for 4DCT ventilation and the irradiated dose. Using 3D-CRT, VMAT, and PT, the percentages of the functional lung regions that received ≥ 5 Gy (fV5) were 26.0%, 21.9%, and 10.7%, respectively; the fV10 were 14.4%, 11.4%, and 9.0%, respectively; and fV20 were 6.5%, 6.4%, and 6.6%, respectively, and the functional mean lung doses (fMLD) were 5.6 Gy, 5.2 Gy, and 3.8 Gy, respectively. These results indicated that PT resulted in a significant reduction in fMLD, fV5, and fV10, but not fV20. The use of PT reduced the radiation to highly functional lung regions compared with those for 3D-CRT and VMAT while meeting all dose constraints.

The effects of helium production, displacement damage on mechanical properties and microstructures were investigated in some specimens such as austenitic stainless steels of SUS304 and SUS316 and a high chromium martensitic steel of HCM12A steels irradiated in a high fluence irradiation facility (HIT) of the University of Tokyo. The simultaneous dual ion (nickel plus helium ions) irradiations were adopted to simulate nuclear irradiation environments such as fast reactor and fusion reactor at HIT to 1 or 10 dpa and to 0, 1, 10, and 100 appm-He at 500, 550, and 600 °C. Thin foils for a transmission electron microscopy (TEM) were prepared with a focused ion beam (FIB) micro-sampling system. After the irradiation, the microstructures were observed by a transmission electron microscope and the irradiation hardening was measured by nano-indentation technique. In this study, the efficient of non-destructive measurement method of surface acoustic wave (SAW) excited by laser beam on the detection of radiation hardening behavior was also examined. Irradiation hardening was observed and the increment was tended to increase with dpa and He/dpa, which was especially effective in the condition of 100 appmHe/dpa even at 550 °C. Non-linear effect on amplitude of the excited SAW was also observed on the ion irradiated materials, and the propagation velocity of SAW was tended to be increased with irradiation dose. It was found that the behaviors of SAWs results were correlated with the changes of mechanical properties. Keywords: Irradiation hardening, Surface acoustic wave, Helium, Displacement damage, He/dpa, Austenitic stainless steel

An in-situ cosmic-dust instrument called the Mercury Dust Monitor (MDM) had been developed as a part of the science payload for the Mio (Mercury Magnetospheric Orbiter, MMO) stage of the joint European Space Agency (ESA)–JAXA Mercury-exploration mission. The BepiColombo spacecraft was successfully launched by an Ariane 5 rocket on October 20, 2018, and commissioning tests of the science payload were successfully completed in near-earth orbit before injection into a long journey to Mercury. MDM has a sensor consisting of four plates of piezoelectric lead zirconate titanate (PZT), which converts the mechanical stress (or strain) induced by dust-particle impacts into electrical signals. After the commencement of scientific operations, MDM will measure the impact momentum at which dust particles in orbit around the Sun collide with the sensor and record the arrival direction. This paper provides basic information concerning the MDM instrument and its predicted scientific operation as a future reference for scientific articles concerning the MDM’s observational data.

We quantified intra-fractional dose variation and organ movement during CT-based 3D-image guided brachytherapy (3D-IGBT) in cervical cancer patients. Fifteen patients who underwent CT-based 3D-IGBT were studied. For all patients, pre-delivery CT for treatment planning after applicator insertion and post-delivery CT after dose delivery without changing the applicator position were acquired. Pre- and post-delivery CT were rigidly fused by matching the inserted applicator and planned dose on pre-delivery CT (pre-delivery dose) was mapped on post-delivery CT (post-delivery dose). D2, D1, and D0.1 cm3 of the rectum and bladder were compared between pre- and post-delivery doses with contours on each CT image. Organ movement and deformation was evaluated using deformation vector fields calculated by deformable image registration between pre- and post-delivery CT. We also evaluated dose variation and DVF between with and without a catheter to control filling. Differences in all DVH parameters were 15% dose difference was found in 13.8% of the fractions in rectum D2 cm3 and in 11.1% of those in bladder D2 cm3. The mean value of DVF for bladder was larger than that of rectum, especially for the superior-inferior (S-I) direction. Insertion catheters in bladder reduced mean dose and DVF variation compared with that of without catheters. In fraction groups with large dose increasing, DVF in the S-I direction was significantly larger than that of other fraction groups. Our results indicated that preparation is needed to reduce changes in the S-I direction affect dose variation.

Isochronal annealing followed by residual resistivity measurements at 12 K was performed in Fe-0.6Ni-0.6Si and Fe-1.5Mn-0.6Si alloys irradiated with 1 MeV proton ions below 70 K, and recovery stages were compared with those of Fe–0.6Ni and Fe–1.5Mn. The effects of silicon addition in the Fe-Ni alloy was observed as the appearance of a new recovery stage at 282–372 K, presumably corresponding to clustering of solute atoms in matrix, and as a change in mixed dumbbell migration at 122–142 K. Silicon addition mitigated the manganese effect in Fe–Mn alloy that is obstructing the recovery of radiation defects. Reduction of resistivity in Fe-Mn-Si alloy also suggested formation of small solute atom clusters.

This paper reports the modification of the High Fluence Irradiation Facility at the University of Tokyo (HIT). The HIT facility was severely damaged during the 2011 earthquake, which occurred off the Pacific coast of Tohoku. A damaged 1.0 MV tandem Cockcroft-Walton accelerator was replaced with a 1.7 MV accelerator, which was formerly used in another campus of the university. A decision was made to maintain dual-beam irradiation capability by repairing the 3.75 MV single-ended Van de Graaff accelerator and reconstructing the related beamlines. A new beamline was connected with a 200 kV transmission electron microscope (TEM) to perform in-situ TEM observation under ion irradiation.

A potential factor dominating the obstacle strength of second phase precipitate particles in dispersion strengthening is the crystallographic mismatch between the matrix phase and the second phase; however, yet this concept has not been fully assessed by experiments and simulations. In the present study, we experimentally investigated the obstacle strength of body centered cubic (bcc) Nb particles and nanometric Nb clusters embedded in hexagonal close packed (hcp) Zr matrix. The bcc Nb is softer than the hcp Zr in terms of shear modulus, whereas from a crystallographic viewpoint, the bcc Nb particles can be nonshearable, strong obstacles because the slip plane inside the particles is not parallel with that in the matrix. Although the bcc Nb is thermodynamically the stable configuration for Nb atoms precipitating from the Zr matrix, in the very early stage of solute agglomeration, the crystal structure of Nb nanoclusters is possibly hcp rather than bcc. The obstacle strength ( α ) was no greater than 0.5 for the Nb nanoclusters, whereas 0.85 ≤ α ≤ 1 for the coarse bcc Nb particles; α = 1 was obtained with the Taylor factor ( M ) of 5.5 and α = 0.85 with M = 6.5, respectively. These results indicate that the bcc Nb particles are strong obstacles, and that the Nb nanoclusters are weak obstacles.

Reactor pressure vessels comprise bainitic steel structures, and are heterogeneous on the mesoscale. Nanoindentation techniques were used to evaluate the hardness of these structures on the microme...

This study investigates the recovery of electric resistivity in pure iron, Fe–0.6Ni and Fe–1.5Mn as related to isochronal annealing following 1 MeV proton irradiation at lower temperature than 70 K, focusing on the relationship between solute atoms and irradiation defects. Both nickel and manganese prevent stage ID recovery, which corresponds to correlated recombination. Stage II recovery is also changed by the addition of a solute, which corresponds to the migration of small interstitial clusters. In both pure iron and Fe–0.6Ni, no evident difference was observed in the stage III region, which corresponds to the migration of vacancies. In contrast, two substages appeared in the Fe–1.5Mn at a higher temperature than stage IIIB appeared in pure iron. These substages are considered to represent the release of irradiation-induced defects, which was trapped by manganese.

Accepted: 2014-05-12, 資料番号: SA1140138000

We studied the grain size dependence of the defect evolution that occurred in a nanocrystalline (NC) Ni and its coarse-grained counterpart under irradiation. The vacancy defects produced during irradiation were investigated via in situ observations of the positron annihilation Doppler broadening spectra. The annihilation line-shape parameter S was measured under beam-on (during irradiation) and beam-off (after irradiation) conditions. We found that different variations in S were observed depending on the grain size; for the coarse-grained specimen, the S measured under beam-on conditions was larger than that observed under beam-off conditions, while for the NC specimen, the S value remained unchanged under beam-on and beam-off conditions. The former result indicated that the vacancy concentration was enhanced during irradiation, due to transient vacancy production. The latter result may imply that defect accumulation was strongly suppressed under irradiation. We also studied the flux dependence of the radiation damage effects for the NC specimen, using high-flux He ions in the flux range of 1.2 × 10 13 –6 × 10 14 ions/(cm 2 s). A slight flux dependence was observed, which was due to microstructural changes at the intersections of the crystallite interfaces under the highest flux irradiation studied.

This study involves the investigation of defect production in iron involving cascade damage processes produced by MeV ion irradiation. Defect configuration after cascade damage is expected to be preserved at low temperatures below Stage I where interstitial atoms begin to migrate. MeV ion beam irradiation of pure iron was carried out at 12 K, and then positron beam Doppler-broadening measurements and electrical resistivity measurements were carried out at the same temperature. By these methods, defect production efficiency, which is defined as the ratio of residual defects to defect formation calculated by the Norgett–Robinson–Torrens (NRT) model, was evaluated for iron irradiated with protons and carbon ions. The defect production efficiency values from the electrical resistivity and the computational calculation coincide well to support the validity of the computational approaches to the phenomenon. The values from the positron beam qualitatively represent the difference in the primary knock-on atom (PKA) energy spectrum of H + and C + , but the values were lower than those obtained from the electrical resistivity measurements and the computational calculation, possibly due to inhomogeneous distribution of vacancies caused by cascades and enhanced mutual annihilation of Frenkel pairs.

Mechanisms of radiation embrittlement of reactor pressure vessel steels remain to be fully understood, particularly the nature of so-called ‘matrix defects’. One possible mechanism is vacancy cluster formation, probably assisted by cascade damage. In order to investigate the effect of copper on the formation and annealing processes of vacancy clusters, ion-irradiated Fe‒C and Fe‒C‒Cu were investigated using a variable energy positron beam. Doppler broadening analysis revealed that vacancy-type defects are produced by ion irradiation and that copper addition reduces the open volume of the defects. Post irradiation annealing suggested the vacancy clusters do not have a substantial role in irradiation hardening.

The positron beam technique has been widely used as a detection tool for vacancy-type defects in solids, especially defects induced by ion irradiation/implantation that are localized near the surface. To extend this technique to other applications, we constructed unique in situ positron beam measurement equipment combined with an ion beam irradiation chamber. This equipment enables us to measure positron beam Doppler broadening during or immediately after irradiation without any sample handling. With this equipment, defect accumulation and evolution in iron and nickel were investigated at room temperature. In addition, the defect accumulation and annealing process was investigated at temperature below stage III to reveal vacancy configurations after cascade, without any thermal migration after the cascade cooling. In this paper, we summarize these results and discuss ideas for future study.

The responses of a piezoelectric lead zirconate titanate (PZT) element to hypervelocity collisions were experimentally studied. In this study, the particles of masses ranging from 0.3 to 10 fg were made to collide with PZT at velocities between 20 and 96 km/s. The amplitude and the corresponding rise time of the single-pulse output signals that were produced in the piezoelectric PZT element were measured to determine the possible collision states. The results revealed an apparently multimodal output; three classes were assumed to be involved in the pulse formation mechanism. The amplitude and rise time were sensitive to the collision velocity. The multimodal behavior implied that the PZT-based cosmic dust detectors should be calibrated according to the class they belong to.

著者人数：13名, Accepted: 2008-08-19, 資料番号: SA1001037000

In the present work, the trapping behavior of deuterium in F82H under irradiation were studied by means of thermal desorption spectrometry (TDS) and TEM. The specimens were first irradiated with 5 keV He+ at 600 °C followed by the additional D 2 + irradiations with the energy of 0.5 keV at RT. Some of the specimens were also irradiated with relatively higher energy of 1 MeV for He+ and 650 keV for D 2 + ions. According to thermal desorption measurements of deuterium and helium after irradiations, deuterium desorption peak shift to higher temperatures of about 30 K were observed for the case with helium irradiations, which attributed to the deuterium trapped by a surroundings of the helium bubbles. In addition, it is also concluded from the thermal desorption measurements of deuterium on re-tempered and as-received specimens without helium irradiations that the latently existing carbides can acts as a potential trapping site for deuterium in F82H.

A cosmic dust monitor for use onboard a spacecraft is currently being developed using a piezoelectric lead zirconate titanate element (PZT). Its characteristics of the PZT sensor is studied by ground-based laboratory impact experiments using hypervelocity particles supplied by a Van de Graaff accelerator. The output signals obtained from the sensor just after the impact appeared to have a waveform that was explicitly related to the particle’s impact velocity. For velocities less than ∼6 km/s, the signal showed an oscillation pattern and the amplitude was proportional to the momentum of the impacting particle. For higher velocities, the signal gradually changed to a single waveform. The rise time of this single waveform was proportional to the particle’s velocity for velocities above ∼6 km/s. The present paper reports on results for the low velocity case and especially discusses the effect of an outer coating of the sensor with a paint, which is used to reduce heating by solar radiation.

A cosmic dust detector is currently being developed using a piezoelectric lead zirconate titanate (PZT) element. The characteristics of the multilayered detector (MD), which was composed of one hundred PZT disks, were investigated by bombarding it with hypervelocity iron particles supplied by a Van de Graaff accelerator. It was confirmed that there was a linear relationship between the signal amplitude observed from MD and the momentum of the particles. As compared with the single-layered detector (SD) that was composed of one PZT disk, it was found that the sensitivity of MD was ∼3 times higher than that of SD within the limits of the experimental conditions.

In situ observation during hydrogen ion implantation was performed with a transmission electron microscope installed in an ion accelerator to investigate the growth process of Zr hydride in Zircaloy-4. To clarify the effect of radiation damage, some samples were irradiated with 4 MeV Ni3+ ions prior to hydrogen implantation. Growth processes of Zr hydrides accompanying the formation of dislocations were observed. The crystallographic relationship between the Zr matrix and Zr hydrides was identical with that found in previous studies: inter- and intragranular hydrides exhibiting a tendency to grow in the (112-0) direction. This growth can be attributed to a shear mechanism in which there are partial dislocations along basal planes. In specimens preirradiated with Ni ions, the growth rate of hydrides was suppressed, but the growth direction was not affected by radiation defects. It was also confirmed that the black spots induced by Ni3+ ion irradiation grew during hydrogen ion implantation, suggesting the f...

A cosmic dust detector using piezoelectric lead zirconate titanate (PZT) is currently being developed for use onboard a spacecraft for the BepiColombo mission. The characteristics of the PZT detector were studied by carrying out hypervelocity impact measurements with iron particles supplied by a Van de Graaff accelerator. The measurements with particle velocities of less than 5 km/s showed a linear relationship between the output voltages obtained from the detector and the particle momenta. This linear relationship obtained was almost independent of the impact angle between the particle and the PZT surface.

The propagation of transverse waves generated acoustically in a piezoelectric element by colliding it with hypervelocity microparticles was studied. The propagation times were measured by a set of multiple electrodes on the surface of the element. The coordinates that the particles struck were determined by combining the propagation times and the velocity of the waves. By using the position-sensitive element, significant deviations between the prior indicated and actually measured orbits were observed. The potential of the present element as part of a steering system is discussed.

The detector characteristics of a pentagonal element were studied by colliding it with hypervelocity micro-particles. A charge-sensitive amplifier was developed for the element of its capacitance ∼10 nF. The output amplitudes were expressed as a linear function of the momentum at collision. Empirical formulas obtained from on-ground experiments could be used for the calibration of the detector. The pentagonal element was potential to measure the momentum during collision from the output amplitude. A set of electrodes on the surface was used to confirm the measurement of the coordinates at collision. A possible application of this pentagonal element on a real-time dust detector was discussed.

The formation of hydrides in zirconium alloy has been one of the essential matters of discussion to maintain mechanical strength of nuclear fuel cladding tubes. In this work, we examined the precipitation process of zirconium hydride by transmission electron microscopy under hydrogen ion irradiation. Zircaloy-4, which has been used extensively as nuclear fuel cladding, was irradiated with hydrogen ion at room temperature to achieve enough hydrogen concentration for precipitation. The growth of hydrides accompanied with dislocations around hydrides was observed under hydrogen implantation. The observed hydride was the γ-hydride phase with fct structure and the orientation relationship was γ ||α as reported previously. As the hydride grew, the dislocations were generated gradually. This process can be explained using a ratchet mechanism suggested by Carpenter. The growth rate became lower according to the approach of other hydrides. This behavior is considered to be influenced by the strain field caused by other hydrides.

To investigate doping-free zirconia, pulsed laser ablation technique was applied to synthesize pure zirconia nanoparticles. Various experimental parameters were investigated by means of microscopic, spectroscopic and diffractmetric techniques to reveal morphology and production yield. It is successful to form cubic and monoclinic phases at nanometer-scale fine particles. The cubic phase has relatively small lattice parameters than the stabilized zirconia.

Cerium dioxide (CeO2) is a well-studied oxide because of its technological applications, such as a major component in the catalysts, stable capacitors and so on. CeO2 with a cubic fluorite structure is also expected as the material for simulating behaviors of uranium dioxide under energetic particle irradiation, which leads high burn-up structure attributable to pressure increase in fuel cladding tubes. In this work, the stability of crystal structure and surface morphology change in CeO2 will be clarified. Polycrystalline samples were irradiated with 300 keV Xe+, 18 MeV I5+, 350 keV O+ and 12 MeV O3+ ions at temperatures from 370 to 1000 K. Microstructural evolutions was investigated with Scanning electron microscopy, Raman Spectroscopy and X-ray diffractometry. Irradiation effects at high temperature were observed as surface etching and resulting bubble formation, however blistering was not detected. Raman spectra and diffraction data indicates diffusion of oxygen vacancies is sufficient at 900 K and above.

Binary AuPd nanoparticles were prepared by sonochemical reduction of solutions containing Au3+, Pd2+ ions and surfactant (SDS: sodium dodecyl sulfate and PEG-MS: polyethylene glycol monostearate). When using SDS as an additive, AuPd nanoparticles became a core-shell structure of Au core and Pd shell. AuPd nanoparticle with core-shell structure has catalytic activity superior to alloyed particle or Pd nanoparticles. In order to study the electronic states of AuPd nanoparticles, positron annihilation Doppler broadening measurements by using slow positron beam (energy range of 0.1 to 10 keV) have been performed for AuPd nanoparticles. The size and shape of the nanoparticles are also examined by using transmission electron microscope (TEM). The differences of Doppler broadening parameters between core-shell, alloyed AuPd, pure Au and Pd particles were found. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The formation processes of vacancy-type defects induced by ion irradiation in nickel were investigated with a variable-energy positron beam Doppler broadening technique in order to find the appropriate experimental condition for in situ positron beam experiments. Nickel ion irradiation at 300–343 K induces an S parameter increase, but the dependence of the S parameter on positron energy is very similar to that of cold-rolled nickel, which suggests positron trapping by small vacancy-type defects such as SFTs. The best experimental condition for investigation of cavity nucleation process by in situ positron beam Doppler experiments is suggested to be around 0.1–0.4 dpa at 773 K.

An experimental investigation of microstructural evolution has been conducted on Fe-15Cr-16Ni irradiated with 4.0 MeV nickel ions. Irradiations proceeded to dose levels ranging from ~0.2 to ~17 dpa at temperatures of 300, 400, 500 and 600°C at displacement rates of 1 x 10-4, 4 x 10-4 and 1 x 10-3 dpa/sec. The swelling was found to monotonically increase with decreases in dpa rate at every irradiation condition studied. The earliest and most sensitive component of microstructure to both temperature and especially displacement rate was found to be the Frank loops. The second most sensitive component was found to be the void microstructure, which co-evolves with the loop and dislocation microstructure.

著者人数: 14名, 資料番号: SA1003696000

We have developed a confocal fluorescence microscope for observation of the dissolution kinetics at various crystal faces under varying conditions. Natural calcite (CaCO3) was chosen for the experimental samples and the dissolution kinetics was estimated from the increase in the pH value of the solution using a fluorescent pH indicator, seminaphthorhodafluors-1. Using this instrument, we investigated not only the difference in dissolution rate among various crystal faces but also the effects of the surface roughness, subsurface structure (such as lattice defects) and inhibitor on the dissolution rate. Among the (1 0 1 4) , (1 0 1 0) and (2 1 3 4) faces of calcite samples, the (1 0 1 4) face dissolved most slowly and the (1 0 1 0) face fastest. Increasing the surface area of (1 0 1 4) face in contact with water by scratching increased the dissolution rate. Introduction of lattice defects on the (1 0 1 4) face by He+ irradiation significantly increased the dissolution rate. Inhibition of the calcite dissolution by La3+ occurred in the order of (1 0 1 4) > (1 0 1 0) > (2 1 3 4) .

Accumulation of vacancy-type defects in iron produced by various ion irradiations at room temperature was investigated with positron beam Doppler broadening technique. Various ion species (He, C, O, Fe) were used for investigation of the effect of PKA energy on vacancy-type defect production. Accumulation of vacancy-type defects leads to sharpening of Doppler broadening spectra, i.e., increase of S parameter. S parameter was measured as a function of ion fluence for various ion species at a fixed positron energy of 15 keV. At the early stage of irradiation, S parameter increases with increasing fluence, and then it reaches some saturated S parameter value that varies with ion species. The saturated S parameter values tend to be higher for heavier ion irradiation. When compared with the incremental change of S parameter at the same low dpa level, heavier ions also lead to a greater change.

The effects of aging and ion irradiation on microstructure stability and hardness change in the joint materials of CuNiBe/316L and CuAl25/316L have been investigated in the present study. The aging at 673 K for 1000 h or Ni ion irradiation at 573 and 673 K to 10 dpa did not promote the interdiffusion and void swelling at the interface. The hardness in both Cu alloys and stainless steel was increased by irradiation, however, it was decreased by aging except for CuNiBe alloy. The hardness change in CuNiBe alloy was larger than that in CuAl25 alloy. The hardness changes would have a significant effect on the mechanical properties of joint materials.

Recently, it has been pointed out that temperature change under irradiation strongly affects the microstructural evolution of materials. From an engineering point of view, it is very important to investigate the effects of temperature change under irradiation up to high damage levels. Ion irradiations were conducted in the High Fluence Irradiation Facility (HIT) up to 25 dpa. Both upward and downward temperature changes were performed with temperature combinations of 350/500 and 500/350 °C. Under irradiation with an upward temperature change, the microstructure in vanadium after the temperature change has been found to approach the microstructure of material irradiated at constant temperature with increasing damage level. On the other hand, significant effects of temperature change appeared in V–4Cr–4Ti–0.1Si at high damage level. Under irradiation with a downward temperature change, coarsening of defects was observed just after the downward temperature change. The microstructure approached the microstructure of the material irradiated at constant temperature with increasing damage level.

Effects of high-fluence irradiation in fusion-relevant helium production condition on defect cluster formation and swelling of reduced activation ferritic/martensitic steels (RAFs), JLF-1 (Fe–9Cr–2W–V–Ta) and F82H (Fe–8Cr–2W–V–Ta), have been investigated. Dual-ion (nickel plus helium ions) irradiation using electrostatic accelerators was adopted to simulate fusion neutron environment. The irradiation has been carried out up to a damage level of 100 displacement per atom (dpa) at around 723 K, at the HIT facility in the University of Tokyo. Thin foils for transmission electron microscopy (TEM) were prepared with a focused ion beam (FIB) microsampling system. The system enabled not only the broad cross-sectional TEM observation, but also the detailed study of irradiated microstructure, since unfavorable effects of ferromagnetism of a ferritic steel specimen were completely suppressed with this system by sampling a small volume in interests from the irradiated material.

著者人数: 11名, 資料番号: SA1003723000

The combination of charged particle irradiation using MeV energy range accelerators and an ultra-low load indentation is a potential technique to study the mechanical property changes of fusion structural materials due to high-energy neutron irradiation. This work was intended to examine the contribution of various defects to irradiation-induced hardening in an Fe–15Cr–20Ni model alloy by means of single/dual-beam ion irradiation and a micro-indentation. In single/dual ion-irradiated specimens, a significant reduction in Frank loop number density was observed in a region where indentation-induced dislocations evolved. It was observed that only Frank loops with diameters of about 20 nm partially survived in the plastically deformed region. In the dual ion-irradiated specimens, cavities shear-deformed along the mass-flow directions were observed in the region beneath the indent. It was concluded through the indentation hardness determination and post-irradiation indentation micro-structural examination that small Frank loops cause hardening to a larger extent than expected from their actual sizes and induce plastic instability by annihilating by interactions with moving dislocations, while clean cavities produced by ion irradiation are not strong deformation barriers as estimated from neutron data.

The evolution of microstructure in vanadium alloys after upward and downward temperature changes has been closely examined. Vanadium alloys have been irradiated in the high fluence irradiation facility at the University of Tokyo (HIT). Irradiations have been performed either at constant temperature of 500°C or in a stepwise temperature sequence of either 350/500°C, 400/500°C, 450/500°C, 500/350°C or 350/500/350°C up to 0.5 or 0.75 dpa. After 350/500°C and 400/500°C temperature change irradiations, small dislocation loops have been observed. The density of these dislocation loops decreased with the pre-irradiation temperature. After 450/500°C irradiation, the microstructure was coarse, indicating that the initial temperature (450°C) was high enough to be in the regime, where the growth of defects mainly occurs. In the case of downward temperature change, microstructures coarser than those of higher temperature irradiations were observed. This apparent anomaly may be understood in terms of the rate theory.

Helium was implanted into high purity Fe and F82H at room temperature up to 2000 appm to investigate helium effects on hardening. Ultra micro-indentation tests were performed on the specimens before and after helium implantation with loads that penetrate in 300 nm depth. After the indentation tests, the specimens were prepared with a focused ion beam (FIB) processing system for transmission electron microscopy (TEM) of the deformed regions. Results of the indentation tests indicated clearly that helium implantation caused hardening for both pure Fe and F82H. For pure Fe, it was also observed by TEM that the propagation of the plastic deformation zone formed during the indentation was limited to the helium-implanted layer, ranging from 600 to 800 nm from the incident surface.

In fusion materials, irradiation of 14 MeV neutrons produces He and H atoms at a high generation rate. The objective of this study is to clarify synergistic effects of He and H on microstructural evolution in pure vanadium and two vanadium alloys including candidate ternary alloy V–5Cr–5Ti. The specimens are irradiated with 12 MeV Ni 3+ ions at 873 K with simultaneous implantation of 1 MeV He + and 350 keV H + ions. Helium and hydrogen implantation ratios are independently controlled at two different He/dpa and H/dpa rates. Dual beam irradiation with heavy ions and He ions or H ions, and single beam irradiation experiments are also performed. Triple beam irradiation strongly enhances growth of cavities and swelling in pure vanadium compared with those under dual beam irradiation with He and single beam irradiation, whereas simultaneous implantation of H without He does not affect cavity growth and swelling. In V–5Cr–5Ti alloy, no cavities are detected without implantation of He. However, Ni, He and H triple beam irradiation is found to enhance swelling. These results are discussed in terms of dislocation and cavity evolution in the irradiated vanadium alloys.

Langmuir–Blodgett films were studied using a variable energy slow-positron beam. We measured the energy spectra of positron annihilation radiation for Cd and Mg eicosanoid films and obtained the V- and S-parameters as a function of the incident positron energy, E. In the V-E curves of Cd eicosanoid films, there were dips at the positron energy whose mean implantation depth corresponding to the first and second Cd 2+ layers from the surface. These dips are interpreted as the result of inhibition of Ps formation by the Cd 2+ ions. The S-parameter was found to be sensitive to chemical composition of the film and also to possible structural change due to heat treatment. Our results suggest that positron beams provide valuable information about the microstructure of the Langmuir-Blodgett films.

The formation and stability of He bubbles in Fe irradiated with 2.5 MeV He to a dose of 1.0×1020 ions/m2 were investigated. The results of positron lifetime and coincidence Doppler broadening (CDB) measurements showed that He bubbles were formed in the He-ion-irradiated Fe. The growth of the He bubbles by the movement and coalescence of bubbles at temperatures higher than 773 K was detected. The He bubbles remained even at the high temperature of 1373 K. In addition, He atoms were also trapped by dislocation loops formed by the irradiation. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A cosmic dust detector for installation on a satellite is currently being developed using piezoelectric lead zirconate titanate (PZT), which can possess both functions of the collector and the transducer. The characteristics of the PZT detector have been studied by bombarding it with hypervelocity particles supplied by a Van de Graaff accelerator. The front surface of the detector used in this study was covered with a white paint to reduce any increase in the temperature due to the solar radiation. There was a linear relationship between the rise time of the signal produced by the detector and the particle's velocities, which were above 10 km/s on impact. This implies that individual particle velocities on impact can be inferred through the empirical formula derived from the data obtained from the PZT detector.

An experimental technique to determine the dual-ion irradiation-induced hardening of solid materials by means of micro-indentation was developed and then applied to evaluate the irradiation response of low activation martensitic steel. Micro-hardness measurements were performed on a low activation Fe-9Cr-2W steel (JLF-1) which was obtained following bombardment of 4 MeV nickel ions up to 1 dpa with simultaneous deposition of helium ions at 0–100 appm He/dpa in a temperature range of 573–873 K. The obtained micro-hardness profiles corresponded to the expected hardness profiles. The increasing He/dpa ratio almost monotonically increased the micro-hardness at 673 K and higher temperatures. However, the irradiation-induced micro-hardness changes were no more than 10% except for very limited cases. Isothermal annealing at temperatures above 773 K caused softening within a thin surface layer of the specimens and only a small amount of helium prohibited the softening.

Thin solid films of poly(di-n-hexylsilane) were irradiated with a variety of high-energy ion beams, electron beams, and 60Co γ-rays of which linear energy transfer (LET) ranges from 0.2 to 1620 eV/nm. The beams caused nonhomogeneous reactions of crosslinking and main chain scission in the films. The molecular weight of the polymer was traced to give the efficiency of crosslinking reactions: G(x) based on the Charlesby−Pinner relationship. The value of G(x) increases from 0.042 to 0.91 with increasing values of LET. We adopt a reaction model in a single ion track to the crosslinking reactions, and the expanding chemical track along an ion trajectory is responsible for the increasing crosslinking G values. The theoretical aspects of the energy distribution in the penumbra area give a good interpretation of the chemical track radii obtained in this study.