Unveiling the effects of Mn, Cr, Al, and Si on the low-temperature tempering behaviors of high-carbon martensite

Zhang, Y.*; 丸澤 賢人*; 工藤 航平*; 諸岡 聡; Gong, W.; Harjo, S.; 宮本 吾郎*; 古原 忠*

Journal of Materials Science & Technology, 275, p.250 - 259, 2026/12

https://doi.org/10.1016/j.jmst.2026.04.015

This study examines how substitutional alloying elements (Mn, Cr, Al, and Si) influence low-temperature tempering reactions in high carbon martensitic steels. Through comprehensive experimental techniques including neutron diffraction et al., the work clarifies how alloying modifies tempering kinetics by affecting carbon diffusion and phase nucleation. Al and Cr strongly suppress martensite tetragonality reduction and carbon redistribution, while retained austenite decomposes in two stages that are selectively delayed by different alloying elements. Overall, the tempering sequence and kinetics are shown to be governed by alloying-dependent control of carbon mobility and phase transformations.

Directional fast neutron detectors for neutron source surveys over large areas

弘中 浩太; 小泉 光生; 持丸 貴則*; 高橋 時音; 山西 弘城*; 若林 源一郎*

Nuclear Instruments and Methods in Physics Research A, 1090, p.171675_1 - 171675_7, 2026/10

https://doi.org/10.1016/j.nima.2026.171675

Directional fast neutron detection is critical for efficient neutron source surveys in nuclear security applications. In this study, we investigate detector geometries and measurement strategies that enable neutron source localization using plastic scintillation detectors without neutron moderation. Two detector configurations were developed: a rod-shaped scintillator equipped with photomultiplier tubes (PMTs) at both ends and a plate-shaped scintillator instrumented with four PMTs at its corners. Angular response measurements to incident neutrons and rectilinear scanning measurements relative to a neutron source were performed. Both detectors exhibited clear angular dependence in neutron count rates attributable to detector geometry. Rectilinear scanning measurements enabled identification of the point of closest approach to the source along the scan path and estimation of the source--detector distance. For the plate-shaped detector, analysis of relative PMT signal strengths provided additional directional information, enabling three-dimensional localization of the neutron source using a single detector. These results demonstrate that plastic scintillation detectors, when combined with appropriate geometries and scanning strategies, can achieve neutron source localization --- which is a key capability for mobile neutron source survey applications.

The KTB monazite fission-track profile; Initial insights into ultra-low temperature thermochronology from a natural laboratory

中嶋 徹*; 末岡 茂; 福田 将眞; King, G. E.*; 田上 高広*

Earth and Planetary Science Letters, 690, p.120184_1 - 120184_9, 2026/09

https://doi.org/10.1016/j.epsl.2026.120184

Recent advancements in "ultra-low temperature" thermochronology have enabled exploration of the thermal evolution of the upper 2 km of the crust, with monazite fission-track (MFT) thermochronology emerging as a promising approach. However, the thermal sensitivity of MFT has mainly been verified through laboratory experiments, without considering geological timescales (10 - 10 years). In this study, we investigated the thermal sensitivity of MFT over geological timescales by analyzing the crustal depth profile of the MFT length from a well-documented thermally stable crustal environment at the German Continental Deep Drilling Program (the KTB). The mean MFT length of the KTB core shows a gradual decrease from the shallow part (9.56 m at 10 m depth) to the deep part (5.50 m at 2725 m depth). This result suggests that the MFTs have been annealed depending on the holding temperature of each sample between 25 and 100 Myr. The MFT length profile observed in the KTB suggests that the partial annealing zone of the MFT system is approximately from 30C up to 80C over geological timescales. The results of this study support the suggestion of previous research that MFT can be employed as an ultra-low temperature thermochronometric method. On the other hand, the temperature range of the partial annealing zone is likely to be narrower than predicted from extrapolation of short-term annealing experiments using artificial semi-tracks by previous research. The existing annealing models should be reviewed using short-term annealing data using confined tracks and long-term natural annealing data, including the results of this study.

Magnetic properties of NdCrGeTiO having spin- antiferromagnetic alternating chains of Cr spins and dimers of Nd moments

長谷 正司*; 池田 真奈美*; 萩原 雅人; 久保田 正人

Journal of Magnetism and Magnetic Materials, 653, p.174193_1 - 174193_7, 2026/09

https://doi.org/10.1016/j.jmmm.2026.174193

We investigated the magnetic properties of NdCrGeTiO, in which Cr spins and Nd moments form spin- antiferromagnetic (AFM) alternating chains and dimers, respectively. The ranges in which an AFM transition appears are narrow( and ). We observed a broad maximum of specific heat and magnetic susceptibility. The maximum indicates the existence of AFM and ferromagnetic (FM) short-range order (SRO) at and , respectively. The entropy shows that disordered components of Nd moments generating the FM SRO remain at (the AFM transition temperature) at , similar to the existence of disordered components of Nd moments generating the AFM SRO at at . The main origin of the AFM and FM SROs is AFM and FM interactions in Nd-Nd dimers (), respectively. A discontinuous AFM-to-FM transition in the interaction occurs between and . The coexistence of the AFM and FM interactions due to compositional inhomogeneity of Ge and Ti likely prevents Nd moments from magnetic ordering in the wide range (). We observed the spin-gap excitation of Cr spins at 7.5 meV in inelastic neutron scattering measurements of NdCrGeTiO. The existence of the spin-gap excitation at 1.8 K indicates no magnetic ordering of Cr spins at K.

Measuring the velocity of fragments produced by high-repetition-rate nanosecond laser pulses; A Technique to visualize the fragments for laser decontamination

小菅 淳; 安東 航太*; 山本 恵輔*; 中嶋 隆*

Optics & Laser Technology, 201, p.115269_1 - 115269_6, 2026/09

https://doi.org/10.1016/j.optlastec.2026.115269

During laser decontamination of metal surfaces an in-situ technique to probe the dynamics of fragments far from the target is highly desired to efficiently collect them. Along this line we develop an optical technique to measure the velocity of fragments produced by high-repetition-rate nanosecond laser ablation of a metal target. By performing the laser scattering measurements at the oblique angle for the fragments at about 20-120 mm height above the stainless steel target (SUS304) during laser ablation with different pulse durations (15-200 ns) at the repetition rate of 200 kHz, we find that the fragments are classified into two velocity groups. The velocity of fast fragments is in the range of 0.1-0.7 m/s, depending on the height and pulse duration, while that for the cloud-like slow fragments is always about 0.05-0.1 m/s at any height for any pulse duration. Our results elucidate the long-term dynamics of ablated fragments during laser decontamination with a high-repetition-rate laser system.

Probabilistic fracture mechanics benchmarking study of PASCAL-SP code with xLPR code regarding primary water stress corrosion cracking

真野 晃宏; 山口 義仁; 勝山 仁哉

International Journal of Pressure Vessels and Piping, 222, p.105792_1 - 105792_11, 2026/08

https://doi.org/10.1016/j.ijpvp.2026.105792

PASCAL-SPは、日本原子力研究開発機構(JAEA)が開発したPFM解析コードであり、加圧水型原子炉及び沸騰水型原子炉の両方の環境における応力腐食割れや疲労等の経年劣化を考慮して配管の破損確率を評価できる。PASCAL-SPの解析結果の信頼性を高めるために、米国NRCがEPRIと共同で開発したPFM解析コードxLPRを用いたベンチマーク解析を実施した。この解析は、共通の解析条件に基づく決定論的解析と確率論的解析から構成される。ベンチマーク解析の結果、決定論的解析と確率論的解析の両方でPASCAL-SPとxLPRがほぼ同じ結果を出力することが確認された。本論文では、使用した解析条件の詳細と、解析結果の比較を示す。

Applicability of instrumented indentation for assessing allowable flaw sizes of circumferentially flawed stainless steel piping

河 侑成; Negyesi, M.*; 長谷川 邦夫; Lacroix, V.*

Journal of Nondestructive Evaluation, Diagnostics and Prognostics of Engineering Systems, 9(3), p.031001_1 - 031001_6, 2026/08

https://doi.org/10.1115/1.4071687

Structural integrity assessment of flawed pipes, as required by ASME B&PV Code Section XI, relies on failure stress calculated by the Limit Load Criterion (LLC). The failure stress is derived from flow stress, which depends on yield and ultimate tensile strengths. Instrumented indentation technique (IIT) is a nondestructive alternative to the conventional tensile testing. A large amount of studies reported that IIT is capable to assess the yield strength and the ultimate tensile strength with 10 % accuracy compared to the tensile testing. By employing IIT, the tensile properties are expected to be obtained nondestructively and directly from the actual pipe material. The benefit of IIT for the analysis of allowable flaw sizes is critically assessed in this study based on experimental data and Code calculations. Intrinsic standard deviations of yield and ultimate tensile strengths for Type 304 stainless steels are discussed in this paper. As a result, IIT method is capable to estimate the flow stress for Type 304 stainless steel within 3.2 % deviation from the result of conventional tensile tests. Then, the allowable circumferential flaw sizes for pipes subjected to tensile loading are obtained based on strength properties assessed by IIT. In addition, the allowable flaw sizes are compared to the allowable flaw sizes derived from the flow stress tabulated in the ASME B&PV Code Section II, Materials. The conclusion is drawn that IIT yields sufficiently accurate estimates of the flow stress for austenitic stainless steel pipes. Moreover, the flow stress determined from the tabulated values in ASME B&PV Code Section II, Materials, is much lower than the actual measured value, resulting in more conservative estimates of allowable flaw sizes. Therefore, IIT is a beneficial method for the LLC analysis.

Real-time inversion of radioactive source distribution using air dose rate measurements via least absolute shrinkage and selection operator method

Shi, W.*; 町田 昌彦; 岡本 孝司*; Luo, X.*; Feng, W.*; Liu, X.*

Reliability Engineering & System Safety, 272, Part1, p.112538_1 - 112538_18, 2026/08

http://doi.org/10.1016/j.ress.2026.112538

深刻な原子力事故時における緊急対応の信頼性は、放射性線源分布をリアルタイムで確実に監視できるかどうかに大きく依存する。しかし、この安全機能は、監視の死角を生じさせる物理的制約や動的な放出を追跡するには静的手法が不十分であるという問題によって大きく制約されている。本研究では、線源推定の信頼性およびロバスト性を向上させるため、時間正則化を導入したLASSO回帰に基づく動的再構成フレームワークを提案する。具体的には、スライディングウィンドウ型の時間ペナルティ機構を導入し、時間ステップ間の線源変化に対してノルム制約を課すことで、物理的連続性を確保する。また、放射線遮蔽や時間的に変動する強度によるバイアスを補正するため、寄与行列および測定ベクトルを正規化した。検証には、内部遮蔽を有する二室モデルを用い、PHITS(モンテカルロシミュレーション)を用いて実施した結果、遠隔測定データから動的線源を高精度に再構成できることが示された。時間正則化は、空間エイリアシングを抑制し、状況認識能力を向上させる。スライディングウィンドウ幅(正則化なし)の場合、ホットスポット位置は大きく変動し、平均絶対誤差の変動量は約であった。一方、では空間的一貫性が改善され、誤差変動量は程度まで低減した。比較解析の結果、精度と計算コストのバランスの観点からが最適であることが示された。本研究は、困難な条件下においても線源位置および強度を高精度で追跡可能とする、動的ハザード評価のためのより信頼性の高い手法を提示するものである。提案手法は、原子力施設における緊急時管理のレジリエンスと安全性を向上させる意思決定支援ツールとしての活用が期待される。

JRR-3シリサイド燃料平衡炉心における照射設備の中性子スペクトル評価手法の確立

中村 剛実; 小笠原 礼羅; 牛島 寛章; 岡田 祐次; 山口 淳史; 堀口 洋徳; 平根 伸彦

JAEA-Technology 2026-008, 39 Pages, 2026/07

JAEA-Technology-2026-008.pdf:2.55MB

研究用原子炉JRR-3での照射研究は、熱中性子から高速中性子までを対象に実施されており、照射効果を正確に評価するためには中性子スペクトルの影響を考慮する必要がある。JRR-3は20MWの高出力炉のため燃料と可燃性吸収体のカドミウムワイヤが燃焼し、燃焼度の均一化や長期運転を目的に定期的に燃料のシャッフリングと交換が実施されている。計算解析で確度良く中性子スペクトルを評価するにはこの燃焼履歴を時間的・空間的に正確に再現する必要があるため評価を難しくしている。そこで燃焼を伴うJRR-3シリサイド平衡炉心の照射設備に対して、中性子スペクトルを簡便に確度良く評価できる手法を検討し、評価結果の妥当性を検証した。本手法は、MCNPコードを用いて各照射場の初期推定スペクトルと応答関数を計算し、さらにAu-Al線やNi線等の中性子フルエンスモニターから測定した反応率を用いてSAND-IIによりアンフォールディングするものである。2023年度から2025年度にかけて特性測定を行い、7サイクル分の中性子フルエンスモニターの実測値を用いてアンフォールディングを行った結果、すべてのケースにおいて反応率のC/Eの値が1.000となり収束が良好であること、実測中性子束との差異が水力照射設備HR-1で0.3%以内、気送照射設備PN-2で0.8%以内、垂直照射設備RG-2で0%であることから解スペクトルの結果が妥当であることが分かった。本手法の適用により広く利用ニーズに応えることができ、JRR-3照射場の信頼性が向上することで、照射研究の推進に大きく寄与することが期待できる。

Prediction of tumor control probability in prostate cancer radiotherapy using a biophysical model incorporating cancer stem cell and hypoxia

嵯峨 涼*; 岩森 賢大*; 松谷 悠佑; 細川 洋一郎*

Computers in Biology and Medicine, 211, p.111743_1 - 111743_10, 2026/07

https://doi.org/10.1016/j.compbiomed.2026.111743

本研究では、前立腺がんの放射線治療効果を精密に予測するため、サイドポピュレーション(SP)を含むがん幹細胞(CSC)の特性と、腫瘍内の酸素効果(OER)を統合した生物物理モデルを開発した。DU145細胞からSPとメインポピュレーション(MP)を分離し、X線照射後のDNA二本鎖切断やコロニー形成による生存率を、低酸素環境(0.1% O)も含めて評価した。これらのデータをMP・SPおよび酸素濃度を考慮したIMKモデルで解析し、分割照射(2、3、7Gy/回)による臨床TCPと比較した。その結果、MP/SP割合、共通のOER、腫瘍内低酸素体積を用いることで、in vitroおよび臨床データを良好に再現できた。さらに、初期DSB生成量が細胞特性と酸素濃度に応じた放射線感受性を決定する主要因であることが示された。開発モデルは、低酸素領域への線量強化など、前立腺がん治療の最適化の貢献が期待できる。