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Quantum critical spin-liquid-like behavior in the $$S$$ = $$frac{1}{2}$$ quasikagome-lattice compound CeRh$$_{1-x}$$Pd$$_x$$Sn investigated using muon spin relaxation and neutron scattering

Tripathi, R.*; Adroja, D. T.*; Ritter, C.*; Sharma, S.*; Yang, C.*; Hillier, A. D.*; Koza, M. M.*; Demmel, F.*; Sundaresan, A.*; Langridge, S.*; et al.

Physical Review B, 106(6), p.064436_1 - 064436_17, 2022/08

 被引用回数:2 パーセンタイル:45.26(Materials Science, Multidisciplinary)

We present the results of muon spin relaxation ($$mu$$SR) and neutron scattering measurements on the Ce-based quasikagome lattice CeRh$$_{1-x}$$Pd$$_x$$Sn ($$x$$ = 0.1 to 0.75). Our $$mu$$SR results reveal the absence of both static long-range magnetic order and spin freezing down to 0.05 K in the $$x$$ = 0.1 sample, which is consistent with neutron scattering results. The weak temperature-dependent plateaus of the dynamic spin fluctuations below 0.2 K in zero field together with its longitudinal-field (LF) dependence indicate the presence of dynamic spin fluctuations persisting even at 0.05 K without static magnetic order. We argue that such a behavior for $$x$$ = 0.1 can be attributed to a metallic spin-liquid-like ground state near the quantum critical point in the frustrated Kondo lattice. The LF-$$mu$$SR study suggests that the out of kagome plane spin fluctuations are responsible for the spin-liquid behavior.



Walker, C.*

NIMS微細構造解析プラットフォーム利用報告書(Internet), 2 Pages, 2021/09



Using natural systems evidence to test models of transformation of montmorillonite

Savage, D.*; Wilson, J.*; Benbow, S.*; 笹本 広; 小田 治恵; Walker, C.*; 川間 大介*; 舘 幸男

Applied Clay Science, 195, p.105741_1 - 105741_11, 2020/09

 被引用回数:1 パーセンタイル:11.57(Chemistry, Physical)



Natural systems evidence for the effects of temperature and the activity of aqueous silica upon montmorillonite stability in clay barriers for the disposal of radioactive wastes

Savage, D.*; Wilson, J.*; Benbow, S.*; 笹本 広; 小田 治恵; Walker, C.*; 川間 大介*; 舘 幸男

Applied Clay Science, 179, p.105146_1 - 105146_10, 2019/10

 被引用回数:13 パーセンタイル:65.58(Chemistry, Physical)



Hydration and degradation of High content Fly ash Silica fume Cement (HFSC)

安楽 総太郎; Walker, C.*; 小田 治恵; 三原 守弘; 本田 明

Proceedings of 15th International Congress on the Chemistry of Cement (ICCC 2019) (Internet), 11 Pages, 2019/09

Ordinary Portland cement based materials used to construct a repository for the geological disposal of nuclear wastes in Japan, have the potential to form a hyperalkaline (pH $$>$$ 12.5) plume that would affect the performance of other repository components. A High volume Fly ash (FA = 40 wt.%) Silica fume (SF = 20 wt.%) Cement (HFSC424) has therefore been developed to avoid the formation of a hyperalkaline plume. Hydration of HFSC424 in ion exchanged water (IEW) at liquid/solid (L/S) mass ratio = 0.5 caused the loss of portlandite within 56 days by the pozzolanic reaction of SF and FA. Hydrated solid phases included calcium (aluminate) silicate hydrate (C(-A)-S-H) gel and ettringite, and the expressed porewater had a pH = 11.7 after a year of hydration at 20$$^{circ}$$C. Leaching of HFSC424 in IEW was consistent with the dissolution of C(-A)-S-H gel and a decrease to pH = 11.1 at L/S = 1000. Leaching of HFSC424 in SW caused the loss of C(-A)-S-H gel and ettringite for L/S $$leq$$ 30 and a rapid decrease in pH = 10.2. This was followed by the precipitation of hydrotalcite, calcite and magnesium silicate hydrate (M-S-H) and a further decrease to pH = 8.8. These hydration and leaching tests demonstrate that HFSC is a suitable material for repository construction to avoid the formation of a hyperalkaline plume.


Formation of metal ion complexes in cementitious porewaters and leachates

Walker, C.*; 安楽 総太郎; 小田 治恵; 三原 守弘; 本田 明

Proceedings of 15th International Congress on the Chemistry of Cement (ICCC 2019) (Internet), 11 Pages, 2019/09

Reaction of cationic metals (M) and anionic ligands (L) to form ML complexes can alter the dissolution of minerals and the concentration levels of elements in solution. A provisional assessment of ML complex formation in ordinary Portland cement (OPC) porewater and leachates was made with the assistance of the geochemical computer program PHREEQC and the Japan Atomic Energy Agency (JAEA) thermodynamic database for geochemical reactions. Thermodynamic properties of ML complexes were either compiled from the literature or estimated by X-Y weighted linear correlation methods. Simulation of OPC hydration and degradation experiments demonstrated that ML complex formation had little effect on the concentrations of K, Na and Ca, and so too therefore the pH of OPC porewater and leachates. Formation of NaL, CaL and MgL complexes caused a significant increase in the concentrations of Mg, Al, Fe, Si, S, and C. Increased concentrations of these elements meant that OPC hydrates were more soluble and more rapidly consumed during the course of OPC degradation.


Investigation of the $$Delta$$$$n$$ = 0 selection rule in Gamow-Teller transitions; The $$beta$$-decay of $$^{207}$$Hg

Berry, T. A.*; Podoly$'a$k, Zs.*; Carroll, R. J.*; Lic$u{a}$, R.*; Grawe, H.*; Timofeyuk, N. K.*; Alexander, T.*; Andreyev, A. N.; Ansari, S.*; Borge, M. J. G.*; et al.

Physics Letters B, 793, p.271 - 275, 2019/06

 被引用回数:5 パーセンタイル:50.19(Astronomy & Astrophysics)

Gamow-Teller $$beta$$ decay is forbidden if the number of nodes in the radial wave functions of the initial and final states is different. This $$Delta$$$$n$$ = 0 requirement plays a major role in the $$beta$$ decay of heavy neutron-rich nuclei, affecting the nucleosynthesis through the increased half-lives of nuclei on the astrophysical $$r$$-process pathway below both $$Z$$ = 50 (for $$N >$$ 82) and $$Z$$ = 82 (for $$N >$$ 126). The level of forbiddenness of the $$Delta$$$$n$$ = 1 $$nu$$1$$g_{9/2} rightarrow pi$$0$$g_{7/2}$$ transition has been investigated from the $$beta^{-}$$ decay of the ground state of $$^{207}$$Hg into the single-proton-hole nucleus $$^{207}$$Tl in an experiment at the ISOLDE Decay Station. From statistical observational limits on possible $$gamma$$-ray transitions depopulating the $$pi$$0$$g^{-1}_{7/2}$$ state in $$^{207}$$Tl, an upper limit of 3.9$$times$$10$$^{-3}$$ % was obtained for the probability of this decay, corresponding to log$$ft >$$ 8.8 within a 95% confidence limit. This is the most stringent test of the $$Delta$$$$n$$ = 0 selection rule to date.


Calcium silicate hydrate (C-S-H) gel solubility data and a discrete solid phase model at 25$$^{circ}$$C based on two binary non-ideal solid solutions

Walker, C.; 須藤 俊吉; 小田 治恵; 三原 守弘; 本田 明

Cement and Concrete Research, 79, p.1 - 30, 2016/01

 被引用回数:66 パーセンタイル:91.09(Construction & Building Technology)



Na-montmorillonite dissolution rate determined by varying the Gibbs free energy of reaction in a dispersed system and its application to a coagulated system in 0.3M NaOH solution at 70$$^{circ}$$C

小田 治恵; Walker, C.; 千野 大輔*; 市毛 悟; 本田 明; 佐藤 努*; 米田 哲朗*

Applied Clay Science, 93-94, p.62 - 71, 2014/05

 被引用回数:7 パーセンタイル:25.07(Chemistry, Physical)

pH12, 70$$^{circ}$$Cの0.3M NaOH水溶液中におけるNaモンモリロナイトの溶解速度について、フロースルー式実験とバッチ式実験とを組合せて調べた。フロースルー式実験ではSiとAlの濃度を変化させた分散系で行い、Naモンモリロナイト溶解速度を溶解反応のギブス自由エネルギー(dGr)の非線形関数として求めた。この溶解速度式を用いてバッチ式実験のシミュレーションを行い、溶解速度式のdGrがより高くなる凝集系への適用性と、凝集系で生じる二次鉱物生成が及ぼす溶解速度への影響を調べた。シミュレーションはNaモンモリロナイト溶解量や溶液中のSiとAlの濃度の実験結果をよく再現することができた。本研究によって、分散系で求めた溶解速度式が、より高いdGrの領域にある凝集系に適用可能であることと、バッチ系での溶液中のSiとAlの濃度がアナルサイムの沈殿によってコントロールされたことを示した。


Port-based plasma diagnostic infrastructure on ITER

Pitcher, C. S.*; Barnsley, R.*; Bertalot, L.*; Encheva, A.*; Feder, R.*; Friconneau, J. P.*; Hu, Q.*; Levesy, B.*; Loesser, G. D.*; Lyublin, B.*; et al.

Fusion Science and Technology, 64(2), p.118 - 125, 2013/08

 被引用回数:4 パーセンタイル:32.98(Nuclear Science & Technology)



Development of a grout database for geological disposal of high-level radioactive waste

津田 秀典; Walker, C.; 新貝 文昭*; 岸 裕和*; 油井 三和

Journal of Nuclear Science and Technology, 49(11), p.1110 - 1113, 2012/11

 被引用回数:4 パーセンタイル:32.44(Nuclear Science & Technology)

Japan Atomic Energy Agency (JAEA) has developed a grout database (GDB) comprising the latest technical data of grout materials relevant to the geological disposal of high-level radioactive waste (HLW). Currently, only newly developed grout materials of low pH cements, superfine spherical silica and colloidal silica, which are expected to provide a target pH under 11 leachate, are included in the GDB. Case examples from on-site works and laboratory based tests that have been published in the literature have been used to add construction and material details to the GDB. The GDB is available online for registered users to obtain and provide data of grout technology.


Development of grouting technologies for HLW disposal in Japan, 1; Overall program and key engineering technologies

藤田 朝雄; 川口 昌尚; Walker, C.; 笹本 広; 油井 三和; 大西 有三*

Proceedings of 7th Asian Rock Mechanics Symposium (ARMS-7) (USB Flash Drive), p.675 - 681, 2012/10



Nuclear engineering of diagnostic port plugs on ITER

Pitcher, C. S.*; Barnsley, R.*; Feder, R.*; Hu, Q.*; Loesser, G. D.*; Lyublin, B.*; Padasalagi, S.*; Pak, S.*; Reichle, R.*; 佐藤 和義; et al.

Fusion Engineering and Design, 87(5-6), p.667 - 674, 2012/08

 被引用回数:12 パーセンタイル:67.11(Nuclear Science & Technology)

The nuclear engineering infrastructure for port-based diagnostics on ITER is presented, including the equatorial and upper port plug generic designs, the adopted modular concept, the loads and associated load response and the remote handling.


Accelerated hydration of high silica cements

Walker, C.; 油井 三和

NEA/RWM/R(2012)3/REV, p.159 - 163, 2012/03



Polymer model for zeolite thermochemical stability

Arthur, R. C.*; 笹本 広; Walker, C.; 油井 三和

Clays and Clay Minerals, 59(6), p.626 - 639, 2011/11

 被引用回数:16 パーセンタイル:46.26(Chemistry, Physical)



Electromagnetic studies of the ITER generic upper port plug

佐藤 和義; 谷口 英二; Pitcher, C. S.*; Walker, C.*; Encheva, A.*; 河野 康則; 草間 義紀

Fusion Engineering and Design, 86(6-8), p.1264 - 1267, 2011/10

 被引用回数:3 パーセンタイル:26.3(Nuclear Science & Technology)



Nuclear technology aspects of ITER vessel-mounted diagnostics

Vayakis, G.*; Bertalot, L.*; Encheva, A.*; Walker, C.*; Brichard, B.*; Cheon, M. S.*; Chitarin, G.*; Hodgson, E.*; Ingesson, C.*; 石川 正男; et al.

Journal of Nuclear Materials, 417(1-3), p.780 - 786, 2011/10

 被引用回数:24 パーセンタイル:86.89(Materials Science, Multidisciplinary)

ITER has diagnostics with machine protection, basic and advanced plasma control, and physics roles. Several are embedded in the inner machine component region. They have reduced maintainability compared to standard diagnostics in ports. They also endure some of the highest nuclear and EM loads of any diagnostic for the longest time. They include: Magnetic diagnostics; Steady-state magnetic sensors on the outer vessel skin; Bolometer camera arrays; Microfission chambers and neutron activation stations to provide key inputs to the real-time fusion power and long-term fluence measurements; mm-wave reflectometry to measure the plasma density profile and perturbations near the core, and the plasma-wall distance and; Wiring deployed around the vessel to service magnetics, bolometry, and in-vessel instrumentation. In this paper we summarise the key technological issues for each of these diagnostics arising from the nuclear environment, recent progress and outstanding R&D for each system.


Isomeric states observed in heavy neutron-rich nuclei populated in the fragmentation of a $$^{208}$$Pb beam

Steer, S. J.*; Podoly$'a$k, Z.*; Pietri, S.*; G$'o$rska, M.*; Grawe, H.*; Maier, K.*; Regan, P. H.*; Rudolph, D.*; Garnsworthy, A. B.*; Hoischen, R.*; et al.

Physical Review C, 84(4), p.044313_1 - 044313_22, 2011/10

 被引用回数:61 パーセンタイル:94.41(Physics, Nuclear)



Plasma boundary and first-wall diagnostics in ITER

Pitcher, C. S.*; Andrew, P.*; Barnsley, R.*; Bertalot, L.*; Counsell, G. G.*; Encheva, A.*; Feder, R. E.*; 波多江 仰紀; Johnson, D. W.*; Kim, J.*; et al.

Journal of Nuclear Materials, 415(Suppl.1), p.S1127 - S1132, 2011/08

 被引用回数:0 パーセンタイル:0.01(Materials Science, Multidisciplinary)

ITER plasma boundary and first-wall diagnostics are summarized in terms of their physical implementation and physics motivation. The challenge of extracting diagnostic signals while maintaining nuclear shielding is discussed, as well as the problems associated with high levels of erosion and redeposition.


A Comparative study of the modelling of cement hydration and cement-rock laboratory experiments

Savage, D.*; Soler, J. M.*; 山口 耕平; Walker, C.; 本田 明; 稲垣 学; Watson, C.*; Wilson, J.*; Benbow, S.*; Gaus, I.*; et al.

Applied Geochemistry, 26(7), p.1138 - 1152, 2011/07

 被引用回数:19 パーセンタイル:49.11(Geochemistry & Geophysics)

放射性廃棄物の地層処分施設で亀裂のグラウトやトンネルのシール材などとしてセメント系材料を使う場合には、化学的反応性に関する潜在的な問題が生起する。処分の長期安全性評価という点からは、セメントと岩盤などとの反応やその変化について定量的にモデル化することが求められる。LCS(Long-term Cement Studies)プロジェクトとして、NDA(UK), Posiva(Finland), 原子力機構のモデリングチーム間で、セメント水和反応及びセメント-岩反応についての室内実験に対するモデリング比較研究を行った。この結果、どちらの実験についても、詳細なパラメータ化の点で顕著な違いはあるものの、主要な反応経路についてはとてもよく理解できており、チーム間でも矛盾しないことが示された。今後、長期スケールにおける鉱物-水反応の評価に役立つような適切なナチュラルアナログやインダストリアルアナログなどの事例に着目したモデリング研究を行うことが望まれる。

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