National Institutes for Quantum and Radiological Science and Technology
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f-d-p 模型を用いた UTe2 を対象とするスピン格子緩和率の理論研究
No full textUTe2 は、高い上部臨界磁場や磁場・圧力下における超伝導多重相などを理由に、スピン三重項超伝導体の有力な候補物質として注目を集めている物質である。我々は、UTe2 の超伝導対称性及び発現機構を明らかにするために、(0,±π,0)方向の反強磁性揺らぎと擬二次元的な Fermi 面を再現する 6 軌道 Hubbard 模型(f-d-p 模型)を構築した。この模型において、オンサイトの Coulomb 相互作用について三次まで摂動展開した超伝導有効相互作用を用いて線形化Eliashberg 方程式を解くと、ポイントノード的なギャップ構造を持つスピン一重項であるAg 状態の超伝導が実現し得ることが我々の先行研究にて示されていた。 本研究では、先行研究で得たポイントノード的な Ag 状態では、ギャップ構造の異方性に起因して、スピン格子緩和率の Hebel-Slichter ピークが観測困難なほど非常に小さくなる可能性を考えた。スピン格子緩和率の計算結果は下図に示したとおりであり、等方的な Ag 状態と比較して、ポイントノード的な Ag 状態では、Hebel-Slichter ピークが確かに小さくなっているものの、無視できないほどの大きさで残ることが明らかとなった。UTe2の実験では、スピン格子緩和率に Hebel-Slichter ピークが観測されておらず、ポイントノード的な Ag 状態はスピン格子緩和率の実験結果と整合していないことが明らかとなった。 本講演では、上記のポイントノード的な Ag 状態についてのスピン格子緩和率の計算結果に加えて、スピン三重項状態である Au, B1u, B2u, B3u 状態についての計算結果を紹介し、UTe2 における超伝導対称性について議論する。さらに、UTe2 におけるスピン格子緩和率への強相関効果を乱雑位相近似の範囲内で議論する予定である。日本物理学会 第80回年次大会（2025）conference presentatio
Development of Ultrahigh-precision Ion Implantation System Based on Laser-cooled Ion Source
No full textNitrogen-vacancy (NV) centers in diamond are gaining attention as room-temperature quantum bits, with potential applications in quantum sensing, quantum information processing, and quantum communication. Precise positioning of NV centers is crucial for creating efficient single-photon sources using optical resonators and quantum memories for quantum interface, etc. Generally, broad ion beam implantation through nanohole fabricated by electron beam lithography has been widely used for precise creation of NV centers. There are several reports of deterministic NV creation by using pulsed fs- or ps-laser irradiations. In addition, focusing ion beam implantation provides a route towards scalable quantum information processing [3-6]. In this study, we are developing an inherently deterministic single-ion implantation method based on a linear Paul trap (LPT) as a single-ion source, since the laser-cooling technique can be applied to the trap system to obtain ultralow-emittance ions and manipulate single ions one by one. The QST system uses doubly charged ions cooled with calcium ions, allowing 100 keV ion implantation in diamond.QUANTUM INNOVATION 2025conference poste
Determination of irradiation dose and measurement time for range verification using PET: toward establishing “pre-irradiation” procedure in proton therapy
No full textBackground and Aims: Recently, “pre-irradiation” procedure is proposed to verify in vivo dose delivery; pencil beams are irradiated at multiple spots just before a main treatment and the range positions are confirmed from the obtained PET images. In this procedure, the irradiation dose and measurement time directly influence the accuracy of range estimation. This study presents a method for predetermining the optimum measurement time (i.e., minimum) corresponding to the irradiation dose to achieve accurate range estimation.Methods: Assuming that the statistical noise in PET measurements obeys the Poisson distribution, the range uncertainties originated from the number of counts and the magnitude of gradient can be estimated by the Fisher's information. In addition, the range difference determined from simulated (i.e., ideal) and measured activity distributions can be estimated by the maximum likelihood estimation (MLE) algorithm. In this study, 100.2-MeV proton beams at the peak doses equivalent to 0.1, 0.5, and 2 Gy were irradiated on polyethylene targets, and the PET measurements were conducted for 300 s soon after the irradiations in both Monte Carlo simulation (using Geant4-v11.2.1) and experiment (conducted at Nagoya Proton Therapy Center); the 1D activity distributions integrated along the depth direction were obtained. From the simulated data, the measurement times when the range uncertainties were expected within 1 mm at 2σ were determined by the Fisher’s information. Then, the actual range differences between the simulations and measurements were determined by the MLE algorithm.Results: From the Fisher’s information based on the simulated data at the peak doses of 0.1, 0.5, and 2 Gy, the range uncertainties were expected within 1 mm at 2σ when the measurement times were 120, 30, and 10 s, respectively. At these measurement times, the actual range differences observed in the measured data were -0.49, 0.98, and 1.34 mm, respectively. The range differences obtained in the actual measurements were consistent with those estimated by the Fisher's information.Conclusions: The results demonstrated the validity of applying the Fisher’s information to determine the minimum measurement time corresponding to an irradiation dose for accurate range estimation using PET in proton therapy.PTCOG 63conference poste
陽子線照射における対向型平面PET検出器での陽電子放出核生成分布計測の散乱線補正に関する研究
No full text[目的] 陽子線照射時に患者体内で生成される陽電子放出核種由来の消滅ガンマ線発生位置の強度分布（Activity分布） 計測で得られる画像により，実際の照射領域を可視化することができる．しかし，計測データに含まれる散乱 線の影響でActivity分布画像の定量性が悪化する．本研究では，画像再構成に散乱線補正法を実装し，散乱線補 正効果を評価検証することを目的とする．[方法] 実験は100.2 MeVの陽子線ペンシルビームをポリエチレンターゲット（8 cm×8 cm×12 cm）に72 Gy（ブ ラッグピーク）照射し，照射直後から30分間のActivity分布計測を行った．計測されるガンマ線エネルギース ペクトルの511 keV周辺（425-650 keV）とその高エネルギー側（510-650 keV）のエネルギーウィンドウに対 応するActivity分布データを導出した．両者の分布の減算処理により散乱線の空間分布データを求めた．平滑化 処理によってノイズを低減した散乱線の空間分布を前者から減算することで散乱線成分を除去したActivity分布 画像を作成した．比較のため，モンテカルロシミュレーション（PHITS 3.26）上に実験と同様の照射・測定系 を構築し，散乱線成分を除去したActivity分布画像を導出した．[結果] 深さ方向に積算した1次元Activity分布の最大値を100%とした場合，100.2 MeV陽子線の8.0 cm飛程位置から 2.0 cm離れた深部10 cm位置のActivity値は散乱補正効果により6.8%から3.1%まで減少した．この値はPHITS で得られた値（3.0%）と同等であった．[結論] ガンマ線エネルギースペクトルを利用したエネルギーウィンドウ法による散乱線補正は非照射領域の散乱線成 分を減少させ，定量性の高いActivity分布画像導出において有用であることを示した．第130回日本医学物理学会学術大会conference presentatio
Neon ion radiotherapy: physics and biology.
No full textNeon ion (20Ne) beam radiotherapy was one of the primary particle therapy candidates investigated during the clinical trials beginning in the 1970s at the Lawrence Berkely National Laboratory (LBNL), which shutdown in the early 1990's. Currently, therapeutic neon ion beams are available at only one clinical facility worldwide, the National Institutes for Quantum Science and Technology (QST) in Chiba, Japan. Recently, neon ion beams were commissioned at QST Hospital as part of the first clinical multi-ion therapy (MIT) program, which aims to improve clinical outcome by escalating higher linear energy transfer (LET) radiation in the tumor for treating therapy-resistant disease. With the advancement of high-precision scanning delivery techniques, neon ion treatments in the present day could be more targeted and safely delivered compared to the first and only clinical application decades prior at LBNL using passive scattering technology. Despite their promising results, pre-clinical investigations of neon ions are scarce outside of Japan and more independent studies are needed. Clinically, neon ion therapy may offer significant benefits for certain malignancies through LET escalation in the tumor, but its limited availability and high costs restrict its current use and adoption. Studies have shown that 20Ne or multi-ion mixtures (4He, 12C, 16O and/or 20Ne) can provide larger degrees of freedom in optimization of dose, LET and RBE, otherwise unattainable with other single ion techniques. Neon ion beams are under investigation in the on-going MIT clinical trials which will establish their broader applicability. Here, a comprehensive review of the technology, physics, radiobiology, and potential clinical applications of neon ion beams is outlined. The status of therapeutic neon ion beams is provided while discussing future research and clinical directions, including technological development of novel particle therapy delivery techniques, such as multi-ion, mini-beam, arc and ultra-high dose rate.journal articl
Spectroscopic Diagnostics of non-Maxwellian Electron Velocity Distribution Function in the Large Helical Device
No full textThis paper reviews studies of non-Maxwellian electron velocity distribution function (EVDF) measured via line emission spectroscopy and spectropolarimetry in the Large Helical Device (LHD). Information on where and under what conditions the non-Maxwellian EVDFs are generated can substantially affect plasma confinement. Since different atomic transitions exhibit different sensitivities to momenta of incident electrons, spectroscopic analysis of line intensities and their polarization enables the investigation of both the shape and anisotropy of the EVDF. Measurement techniques and their results are summarized across a broad temperature range, covering both edge and core plasmas in LHD. The results are compared with plasma parameters obtained from other diagnostic systems, and the dynamics of passing and trapped electrons are discussed.journal articl
放射化学Ⅱ（千葉大学）
No full text１．放射線の特性と物質との相互作用２．放射性元素①３．放射性元素②４．放射線の生体への影響５．放射化学の応用①６．原子炉と核エネルギー７．放射化学の応用②放射化学Ⅱconference presentatio
Integrated operation scenarios: Chapter 6 of the special issue: on the path to tokamak burning plasma operation
No full textHere we report the progress of the development and optimization of operational scenarios for ITER and beyond, focusing upon baseline, hybrid, and steady-state scenarios since 2007. This includes advancements made by the integrated operation scenarios (IOS) topical group of the international tokamak physical activity as well as contributions from the broader tokamak community. The key area of research involves developing IOSs that encompass tokamak physics, operation, and technology by utilizing integrated modeling and control strategies. This requires leveraging available actuators to simultaneously control plasma position and shape, MHD activities that could lead to disruptions, transport, plasma-wall interaction and power exhaust, fuel cycle, fusion burn, and tritium breeding. The control extends from the plasma initiation phase, through the current ramp-up, flattop, start and end of the fusion burn, and current ramp-down, to the plasma termination phase. A review of the currently developed scenarios and modeling is provided in terms of (i) optimizing plasma initiation in ITER, (ii) preparing for the low activation phase to fully commission all tokamak systems and establish and validate physics and scenario conditions in preparation for deuterim-tritium (DT) operation, (iii) developing and preparing baseline and hybrid scenarios to demonstrate the feasibility of achieving these regimes within device constraints, (iv) exploring steady-state scenarios to meet ITER’s steady-state goals, (v) evaluating and preparing actuators for ITER, (vi) developing integrated control solutions using shared actuators. The most notable achievements include; (i) the development of ITER demonstration discharges by matching various dimensionless parameters, (ii) the development of scenarios in an ITER-like tungsten environment and DT operation, and (iii) the development of scenarios in superconducting tokamaks, enabling long-pulse operations with similar coil constraints to ITER. Along with these significant achievements, outstanding issues and recommendations for further research and development are provided. Importantly, this study goes beyond simply updating the ITER Physics Basis; it carries profound implications for the broader field of burning plasma research, offering valuable insights and guidance for the next generation of fusion experiments and devices.journal articl
Development of a Hybrid Fast Ion Transport Code with Bounce Time-Step-Based Orbit-Following and Drift Orbit-Following
No full textWe developed a bounce-time-based (BT) orbit-following Monte-Carlo code in order to calculate a fast ion transport in the previous work as an extension of the OFMC code in QST. In the BT method, we take a bounce time as a time step of the orbit following for the purpose of reducing computational resources. However, the BT method code has limitations in its realistic application. In order to reduce the limitation, we have developed a hybrid code with the BT method and a drift orbit-following method. In the code, we can switch the methods depending on conditions for each purpose. With using this hybrid code, we have reduced the difference between the BT method and drift orbit-following method in the distribution of fast ions and heating in the plasma central region, which was observed in the previous work, and have been able to adopt a realistic first wall as a loss boundary instead of a separatrix. We have also applied this hybrid approach to handle a fast ion transport in a toroidal field ripple. The hybrid calculation well reproduced the profiles of several quantities obtained by the drift orbit calculation alone while reducing the calculation time.journal articl
分子注入法による近接２NV含有走査NVプローブの開発
No full text本研究では近接NVを含有する走査NVプローブの作製を試みた。研磨及びレーザー加工により50 µm程のダイヤモンドチップとし、FIB加工によりピラー形状に先鋭化する。音叉型水晶振動子にタングステンワイヤーを取り付け、その先端にチップを取り付ける。C32N8H18分子イオンを注入・アニールしたダイヤモンドにおいてNV中心からの蛍光像及びODMR測定により、単1NV、２NVの生成を確認した。2NV含有ピラープローブ作製へ向けた結果について報告する。第86回応用物理学会 秋季学術講演会conference poste