National Institutes for Quantum and Radiological Science and Technology
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Unveiling the nature of cathodoluminescence from photon statistics
No full textCathodoluminescence (CL), the emission of light induced by accelerated free electrons, has been extensively utilized in various applications, such as displays, streak cameras, and high-spatialresolution analysis of optical materials, surpassing the diffraction limit of light. Despite its long history, the photon statistics of CL have only recently been examined, revealing unexpectedly large bunching of photons. Here we find that this peculiar photon bunching contains information of intervening excitation processes before the photon emission, which can be extracted from the photon statistics within each excitation event by a single free electron. Using this approach, we experimentally unveiled the statistical differences of coherent CL involving a single electromagnetic interaction process and incoherent CL involving multiple excitation processes. The developed formulation is universally applicable for particle generation processes in general to investigate the nature of cascade reactions.journal articl
Development of the Protection System for JT-60SA Superconducting Magnet Against Vacuum Degradation
No full textThe JT-60SA project succeeded in commissioning test toward the first plasma in 2023 under a framework: the Satellite Tokamak Programme of the Broader Approach Agreement between EU and Japan. JT-60SA is a tokamak type magnetic confinement device with a superconducting magnet system developed and operated at the Quantum Science and Technology institute (QST) in Japan. The magnet system consists of 18 Toroidal Field coils, 6 Equilibrium Field coils, and 4 modules of Central Solenoids, and all the coils are superconducting magnets. In the first commissioning, during 2020 - 2021, JT-60SA has experienced a discharge incident at the EF1 magnet. As a conclusion of the investigation of the incident, it turned out that the insulation resistance of the magnet system was insufficient. Although the insulation was partly reinforced, the voltage holding under accidentally arising Paschen conditions was not improved enough for the recent operation (OP-1, 2023). To prevent the magnet system from discharging during vacuum degradation, a vacuum monitoring system must be prepared to detect vacuum degradation and ramp down the magnet current immediately in case of unexpected vacuum degradation. In this article, the development of the vacuum monitoring system, operational results, and the future plan of the system will be described.journal articl
Diamagnetic Energy Measurements and evaluation of the poloidal beta and internal inductance during the first operational phase at JT-60SA
No full textThis paper reports on the evaluation of the diamagnetic energy using diamagnetic loops in JT-60SA, the largest operating tokamak in the world, and revisits the physics behind the evaluation of poloidal beta (βp) and internal inductance (li). During the first operation phase of JT-60SA, diamagnetic measurements were utilized in assessing parameters related to plasma equilibrium, such as stored energy, βp, and li. The evaluated stored energy is above 200 kJ with 1 MJ electron cyclotron heating, and we observed the li rise from around unity to above 2 during the plasma current ramp- down phase. The diamagnetic measurements successfully operated throughout the discharge duration, which is above 10 s, with low measurement errors. The correction of the error arising from the interaction between diamagnetic measurements and superconducting coils, as well as the detailed estimation of these errors, are discussed in detail. Furthermore, the physics behind the rise in li is revealed by using both the JT-60SA experiment and numerical simulations.journal articl
Development of a deep learning-based model to evaluate changes during radiotherapy using cervical cancer digital pathology.
No full textThis study aims to create a deep learning-based classification model for cervical cancer biopsy before and during radiotherapy, visualize the results on whole slide images (WSIs), and explore the clinical significance of obtained features. This study included 95 patients with cervical cancer who received radiotherapy between April 2013 and December 2020. Hematoxylin-eosin stained biopsies were digitized to WSIs and divided into small tiles. Our model adopted the feature extractor of DenseNet121 and the classifier of the support vector machine. About 12?400 tiles were used for training the model and 6000 tiles for testing. The model performance was assessed on a per-tile and per-WSI basis. The resultant probability was defined as radiotherapy status probability (RSP) and its color map was visualized on WSIs. Survival analysis was performed to examine the clinical significance of the RSP. In the test set, the trained model had an area under the receiver operating characteristic curve of 0.76 per-tile and 0.95 per-WSI. In visualization, the model focused on viable tumor components and stroma in tumor biopsies. While survival analysis failed to show the prognostic impact of RSP during treatment, cases with low RSP at diagnosis had prolonged overall survival compared to those with high RSP (P?=?0.045). In conclusion, we successfully developed a model to classify biopsies before and during radiotherapy and visualized the result on slide images. Low RSP cases before treatment had a better prognosis, suggesting that tumor morphologic features obtained using the model may be useful for predicting prognosis.journal articl
Effects of temperature on the decomposition of PTFE induced by electron beam irradiation
No full textThe effect of temperature on the irradiation-induced decomposition of polytetrafluoroethylene (PTFE), a representative fluorocarbon polymer, was investigated to improve the energy efficiency of the recycling process. The weight loss of PTFE was 18%, 33%, 64%, and 91% by the irradiation with a dose of 7.5 MGy (dose rate:1.0 kGy/s) at 30°C, 120°C, 200°C, and 270°C, respectively. During the electron beam irradiation of PTFE powders under an oxygen atmosphere, a greater weight loss of PTFE was observed at higher irradiation temperatures. At 370°C, PTFE powder is completely converted to gaseous components with an absorbed dose of 5.0 MGy; the primary product was identified as an oxidized fluorocarbon (C?F??O?). A lower dose rate (0.1 kGy/s) reduced the required absorbed dose for PTFE decomposition to 80% level. Post-irradiation analyses of the PTFE residues using TGA, SEM-EDX, and FT-IR consistently showed that higher irradiation temperatures accelerated the production of oxidized fluorocarbons and further oxidized gaseous products evaporating from the PTFE residue. XRD analysis showed that high-temperature irradiation also increased the crystallite size to 37±5 nm after irradiation at 270°C, which is nearly double the size of non-irradiated PTFE (21±2 nm). High-temperature irradiation significantly accelerated the oxidation and weight loss of PTFE, offering a promising method for enhancing the energy efficiency of PTFE recycling.journal articl
Selective synthesis of large-area monolayer tin sulfide from simple substances
No full textBoth tin monosulfide (SnS) and tin disulfide (SnS2) are stable layered materials with potential for spin?valleytronic devices and photodetectors. Notably, monolayer SnS, owing to its low symmetry, exhibits interesting properties such as ferroelectricity, shift-current, and a persistent spin helix state in the monolayer limit. However, creating atomic-thickness crystals of SnS is challenging owing to the enhanced interlayer interactions caused by lone pair electrons, unlike SnS2. Here, we demonstrate that p-type SnS can be selectively grown by simply varying the sulfur vapor concentration relative to tin using single-element precursors. Additionally, we show that monolayer SnS crystals, up to several tens of micrometers in scale, can be easily and safely obtained by high-temperature etching of bulk SnS in a pure nitrogen gas atmosphere. These findings pave the way for device applications based on high-quality tin sulfide.journal articl
Spin-valley coupling enhanced high-TC ferromagnetism in a non-van der Waals monolayer Cr2Se3 on graphene
No full textSpin-valley magnetic ordering is restricted to layered van der Waals type transition-metal dichalcogenides with ordering temperatures below 55 K. Recent theoretical studies on non-van der Waals structures have predicted spin-valley polarization induced semiconducting ferromagnetic ground states, but experimental validation is missing. We report high-Curie temperature (TC ~ 225 K)metallic ferromagnetism with spontaneous spin-valley polarization in monolayer Cr2Se3 on graphene. Angle-resolved photoemission spectroscopy (ARPES) reveals systematic temperature-dependent energy shifts and splitting of localized Cr 3 d↑-t2g bands, accompanied by occupancy of the itinerant Cr 3d-eg valleys. The t2g-eg spin-valley coupling at the K/K’ points of hexagonal Brillouin zone leads to ferromagnetic ordering. Circular dichroism in ARPES shows clear evidence of spin-valley polarized states. Comparison with bilayer and trilayer Cr2Se3 reveals the crucial role of valley carrier density in enhancing TC and provides a guiding principle to realize 2D ferromagnetism at higher temperatures in non-van der Waals materials.journal articl
Structural basis of cuproenzyme nitrite reduction at the level of a single hydrogen atom
No full textHydrogen (H) atoms account for about half the atoms in biomacromolecules and are essential for their biochemical properties such as enzymatic functions. Obtaining precise enzyme structures that include all the H atoms allows a deeper understanding of their structure-function relationships. Copper-containing nitrite reductases (CuNIRs) catalyze transformation of nitrite to nitric oxide, which has impacts on geochemical, agricultural, and medical health fields. Despite intense research efforts, the dynamics of H atoms during the enzymatic reaction of CuNIRs are unknown and hence the catalytic mechanism remains unclear. We performed neutron crystallography to shoot a single H-atom resolution picture of a CuNIR in complex with nitrite. We found that nitrite binds on the catalytic Cu center as NO2- and not as protonated HNO2. Our X-ray data and quantum chemical calculation show that NO2- is in an electron-localized state that can facilitate N-O bond cleavage after receiving an electron. The catalytic residues, AspCAT and HisCAT, are deprotonated and protonated, respectively, suggesting that HisCAT is the point of departure of the proton transfer sequence. Quantum chemical calculations show that the neutron structure is consistent with the Cu(II) state and that the highly polarized state of the catalytic site is stabilized by the permittivity of solvent molecules filling a water channel. Subatomic resolution X-ray structures of the AspCAT-to-Asn mutants, which mimic the protonated state of AspCAT, were also determined to investigate the involvement of protonated AspCAT in the reaction. Our crystallographic data and quantum chemical calculations reveal in detail the first step of the CuNIR reaction.journal articl
ITER TFコイル製作における電気絶縁設計と絶縁含浸技術の確立
No full textThe National Institutes for Quantum Science and Technology （QST） have completed the manufacturing of nine ITER TF coils. In TF coil manufacturing technologies, insulation is one of the most critical techniques because insulation failure can directly lead to TF coil scrapping. Therefore, QST developed insulation techniques via trials and with the cooperation of manufacturers. In addition, COVID-19 has influenced impregnation work in WPs and coil case assemblies. Alternative resins with especially low viscosity were developed to overcome this difficulty. Finally, based on the experience of TF coil insulation, insulation failure in JT-60SA superconducting coils was repaired. As a result, the first plasma was achieved in October 2023.journal articl
Development of a Novel Positron Emission Tomography Probe Deuterated [18F]FE-TMP ([18F]FE-TMP-d4), an Antagonist of Escherichia coli Dihydrofolate Reductase, for Reporter Gene Imaging of the Brain
No full text[18F]Fluoroethoxy trimethoprim ([18F]FE-TMP, [18F]2), a unique antagonist of bacterial dihydrofolate reductase (ecDHFR), has been developed as a reporter gene imaging agent. Here, we developed new PET probes based on TMP. Simulations predicted that hydrophobic interactions around the benzene ring of 2 contributed to binding with ecDHFR. The more lipophilic fluoropropyl-TMP analog (3) showed a higher binding affinity for ecDHFR than 2. However, 18F-labeled 3 ([18F]3) underwent 18F-defluorination during PET imaging of ecDHFR-transfected mice. Subsequently, we evaluated FE-d4 analog (5) as a candidate exhibiting greater in vivo stability than 2. Metabolite analysis showed a lower contamination of radiolabeled metabolites in mouse brains with 18F-labeled 5 ([18F]5) than [18F]2. PET imaging with [18F]5 of a non-human primate brain was characterized by a distinct signal/noise ratio, which allowed in vivo visualization of brain circuits expressing the reporter gene, demonstrating the superior potential of [18F]5 as a PET probe for reporter gene imaging of the brain.journal articl