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論文

Micro- to nano-scale areal heterogeneity in pore structure and mineral compositions of a sub-decimeter-sized Eagle Ford Shale

Wang, Q.*; Hu, Q.*; Zhao, C.*; Yang, X.*; Zhang, T.*; Ilavsky, J.*; Kuzmenko, I.*; Ma, B.*; 舘 幸男

International Journal of Coal Geology, 261, p.104093_1 - 104093_15, 2022/09

https://doi.org/10.1016/j.coal.2022.104093
 被引用回数：5 パーセンタイル：66.48(Energy & Fuels)

To understanding the spatial heterogeneity of mineral and pore structure variations in fine-grained shale, microscale X-ray fluorescence (micro-XRF) mapping, (ultra-) small-angle X-ray scattering [(U)SAXS] and wide-angle X-ray scattering were applied for two samples from a piece of Eagle Ford Shale in South Texas. Thin section petrography and field emission-scanning electron microscopy, X-ray diffraction (XRD), total organic carbon, and pyrolysis were also utilized to investigate the potential spatial heterogeneity of pore types, mineral and organic matter compositions for both samples. Overall, the siliceous-carbonate mineral contents in these carbonate-rich Eagle Ford Shale vary between laminations at mm scales. By analyzing six selected sub-samples on each of two samples with X-ray scattering and XRD techniques, nm-sized pores are mainly interparticle ones in the higher calcite regions, where the porosity is also relatively lower, while the lower calcite regions consist of both interparticle and intraparticle pore types with higher porosity. Finally, the micro-XRF and (U)SAXS are combined to generate porosity distribution maps to provide more insights about its heterogeneity related to the laminations and fractures at our observational scales.

論文

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

https://doi.org/10.1103/PhysRevB.106.064436
 被引用回数：2 パーセンタイル：32.25(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.

論文

Fine structure in the $$alpha$$ decay of the 8$$^{+}$$ isomer in $$^{216,218}$$U

Zhang, M. M.*; Tian, Y. L.*; Wang, Y. S.*; Zhang, Z. Y.*; Gan, Z. G.*; Yang, H. B.*; Huang, M. H.*; Ma, L.*; Yang, C. L.*; Wang, J. G.*; et al.

Physical Review C, 106(2), p.024305_1 - 024305_6, 2022/08

https://doi.org/10.1103/PhysRevC.106.024305
 被引用回数：3 パーセンタイル：64.25(Physics, Nuclear)

The extremely neutron-deficient even-even uranium isotopes $$^{216,218}$$U were produced in the complete-fusion reactions induced by impinging $$^{40}$$Ar and $$^{40}$$Ca ions on $$^{180,182,184}$$W targets. Fusion evaporation residues were separated in flight by the gas-filled recoil separator SHANS (Spectrometer for Heavy Atoms and Nuclear Structure) and subsequently identified using the recoil-$$alpha$$-correlation method. In this paper, we report on new $$alpha$$-decay activities with $$E_{alpha} = 10163(27)$$ keV for $$^{216}$$U and $$E_{alpha} = 10073(16)$$ keV for $$^{218}$$U, which decay from the 8$$^{+}$$ isomeric states of $$^{216,218}$$U into the 2$$^{+}$$ states of their daughter nuclei $$^{212,214}$$Th, respectively. The new results extend the systematics of the $$alpha$$-decay fine structure for the $$N$$ = 124 and 126 even-even isotones.

論文

The $$^{59}$$Fe(n,$$gamma$$)$$^{60}$$Fe cross section from the surrogate ratio method and its effect on the $$^{60}$$Fe nucleosynthesis

Yan, S. Q.*; Li, X. Y.*; 西尾 勝久; Lugaro, M.*; Li, Z. H.*; 牧井 宏之; Pignatari, M.*; Wang, Y. B.*; Orlandi, R.; 廣瀬 健太郎; et al.

Astrophysical Journal, 919(2), p.84_1 - 84_7, 2021/10

https://doi.org/10.3847/1538-4357/ac12ce
 被引用回数：1 パーセンタイル：8.53(Astronomy & Astrophysics)

The long-lived $$^{60}$$Fe (with a half-life of 2.62 Myr) is a crucial diagnostic of active nucleosynthesis in the Milky Way galaxy and in supernovae near the solar system. The neutron-capture reaction $$^{59}$$Fe(n,$$gamma$$)$$^{60}$$Fe on $$^{59}$$Fe (half-life=44.5 days) is the key reaction for the production of $$^{60}$$Fe in massive stars. This reaction cross section has been previously constrained by the Coulomb dissociation experiment, which offered partial constraint on the E1 $$gamma$$-ray strength function but a negligible constraint on the M1 and E2 components. In this work, for the first time, we use the surrogate ratio method to experimentally determine the $$^{59}$$Fe(n,$$gamma$$)$$^{60}$$Fe cross sections in which all the components are included. We derived a Maxwellian-averaged cross section of 27.5$$pm$$3.5 mb at $$kT$$ = 30 keV and 13.4$$pm$$1.7 mb at $$kT$$ = 90 keV, roughly 10%-20% higher than previous estimates. We analyzed the impact of our new reaction rates in nucleosynthesis models of massive stars and found that uncertainties in the production of $$^{60}$$Fe from the $$^{59}$$Fe(n,$$gamma$$)$$^{60}$$Fe rate are at most 25$$%$$. We conclude that stellar physics uncertainties now play a major role in the accurate evaluation of the stellar production of $$^{60}$$Fe.

論文

Dynamical response of transition-edge sensor microcalorimeters to a pulsed charged-particle beam

奥村 拓馬*; 東 俊行*; Bennet, D. A.*; Caradonna, P.*; Chiu, I.-H.*; Doriese, W. B.*; Durkin, M. S.*; Fowler, J. W.*; Gard, J. D.*; 橋本 直; et al.

IEEE Transactions on Applied Superconductivity, 31(5), p.2101704_1 - 2101704_4, 2021/08

https://doi.org/10.1109/TASC.2021.3067793
 被引用回数：1 パーセンタイル：10.62(Engineering, Electrical & Electronic)

超伝導転移端センサー(TES)マイクロ熱量計は、優れたエネルギー分解能と高い効率を持った、加速器施設での実験に理想的なX線検出器である。高強度パルス荷電粒子ビームを用いたTES検出器の性能を研究するために、日本の陽子加速器研究施設(J-PARC)でパルスミュオンビームを用いてX線スペクトルを測定した。X線エネルギーの実質的な時間的シフトがパルスミュオンビームの到着時間と相関していることを発見した。これは、最初のパルスビームからのエネルギー粒子の入射によるパルスパイルアップによって合理的に説明された。

論文

Deexcitation dynamics of muonic atoms revealed by high-precision spectroscopy of electronic $$K$$ X rays

奥村 拓馬*; 東 俊行*; Bennet, D. A.*; Caradonna, P.*; Chiu, I. H.*; Doriese, W. B.*; Durkin, M. S.*; Fowler, J. W.*; Gard, J. D.*; 橋本 直; et al.

Physical Review Letters, 127(5), p.053001_1 - 053001_7, 2021/07

https://doi.org/10.1103/PhysRevLett.127.053001
 被引用回数：15 パーセンタイル：80.44(Physics, Multidisciplinary)

超伝導遷移エッジ型センサーマイクロカロリメーターを用いて、鉄のミュー原子から放出される電子$$K$$X線を観測した。FWHMでの5.2eVのエネルギー分解能により、電子特性$$K$$$$alpha$$および$$K$$$$beta$$X線の非対称の広いプロファイルを約6keVの超衛星線$$K$$$$alpha$$線とともに観察することができた。このスペクトルは、電子のサイドフィードを伴う、負ミュオンと$$L$$殻電子による核電荷の時間依存スクリーニングを反映している。シミュレーションによると、このデータは電子$$K$$殻および$$L$$殻の正孔生成と、ミュオンカスケードプロセス中のそれらの時間発展を明確に示している。

論文

Optimization of a slab geometry type cold neutron moderator for RIKEN accelerator-driven compact neutron source

Ma, B.*; 勅使河原 誠; 若林 泰生*; Yan, M.*; 橋口 隆生*; 山形 豊*; Wang, S.*; 池田 裕二郎*; 大竹 淑恵*

Nuclear Instruments and Methods in Physics Research A, 995, p.165079_1 - 165079_7, 2021/04

https://doi.org/10.1016/j.nima.2021.165079
 被引用回数：2 パーセンタイル：33.7(Instruments & Instrumentation)

理研加速器駆動型小型中性子源における冷中性子モデレータの最適化を行った。安全かつ管理の容易な物質であるメシチレンをモレデータ材として選択し、粒子・重イオン輸送計算コードシステム(PHITS)を用いて、20Kメシチレンモデレータに室温ポリエチレン(PE)プレモデレータ組み合わせ、スラブ形状で結合した冷中性子の最適化を行った。冷中性子強度を増加させるために、メシチレンとPEの厚さ, 反射体、及び遮へい配置のパラメータを検討した。中性子発生ターゲットから2mの位置で冷中性子強度1.15$$times$$10$$^{3}$$n/cm$$^{2}$$/$$mu$$Aを達成した。これは現在のPEモデレータの12倍である。メシチレンが冷中性子モデレータ材料として魅力的なモデレータ材であることを示した。

論文

New $$alpha$$-emitting isotope $$^{214}$$U and abnormal enhancement of $$alpha$$-particle clustering in lightest uranium isotopes

Zhang, Z. Y.*; Yang, H. B.*; Andreyev, A. N.; Liu, M. L.*; Ma, L.*; 他37名*

Physical Review Letters, 126(15), p.152502_1 - 152502_6, 2021/04

https://doi.org/10.1103/PhysRevLett.126.152502
 被引用回数：44 パーセンタイル：96.44(Physics, Multidisciplinary)

A new $$alpha$$-emitting isotope $$^{214}$$U, produced by the fusion-evaporation reaction $$^{182}$$W($$^{36}$$Ar,4n)$$^{214}$$U, was identified by employing the gas-filled recoil separator SHANS and the recoil-$$alpha$$ correlation technique. More precise $$alpha$$-decay properties of even-even nuclei $$^{216,218}$$U were also measured in the reactions of $$^{40}$$Ar, $$^{40}$$Ca beams with $$^{180,182,184}$$W targets. By combining the experimental data, improved $$alpha$$-decay reduced widths $$delta$$$$^{2}$$ for the even-even Po-Pu nuclei in the vicinity of the magic neutron number ${it N}$ = 126 are deduced. Their systematic trends are discussed in terms of the ${it N}$ $$_{it p}$$ ${it N}$ $$_{it n}$$ scheme in order to study the influence of proton-neutron interaction on $$alpha$$ decay in this region of nuclei. It is strikingly found that the reduced widths of $$^{214,216}$$U are significantly enhanced by a factor of two as compared with the ${it N}$ $$_{it p}$$ ${it N}$ $$_{it n}$$ systematics for the 84 $$leq$$ ${it Z}$ $$leq$$ 90 and ${it N}$ $$<$$ 126 even-even nuclei. The abnormal enhancement is interpreted by the strong monopole interaction between the valence protons and neutrons occupying the $$pi$$1${it f}$ $$_{7/2}$$ and $$nu$$1${it f}$ $$_{5/2}$$ spin-orbit partner orbits, which is supported by the large-scale shell model calculation.

論文

Mesoporous alumina-titania composites with enhanced molybdenum adsorption towards medical radioisotope production

Benu, D. P.*; Earnshaw, J.*; Ashok, A.*; 土谷 邦彦; Saptiama, I.*; Yuliarto, B.*; Suendo, V.*; Mukti, R. R.*; 福光 延吉*; 有賀 克彦*; et al.

Bulletin of the Chemical Society of Japan, 94(2), p.502 - 507, 2021/02

https://doi.org/10.1246/bcsj.20200282
 被引用回数：11 パーセンタイル：65.6(Chemistry, Multidisciplinary)

本研究は、TiO$$_{2}$$含有量を変化させたメソポーラスAl$$_{2}$$O$$_{3}$$-TiO$$_{2}$$複合材料の製造開発及び医療用放射性同位元素の製造のためのMo吸着剤の性能向上のために行った。TiO$$_{2}$$の含有量の増加は、元の形態を変えることなく、Al$$_{2}$$O$$_{3}$$表面へのより多くのTiO$$_{2}$$ナノ粒子の形成を促進する。開発したAl$$_{2}$$O$$_{3}$$-2.5%Ti及びAl$$_{2}$$O$$_{3}$$-5%Tiのアルミナ試料はアモルファスであったが、Al$$_{2}$$O$$_{3}$$-10%Tiでは、TiO$$_{2}$$がAl$$_{2}$$O$$_{3}$$表面に被覆されていた。一方、TiO$$_{2}$$の添加により、比表面積はAl$$_{2}$$O$$_{3}$$の177m$$^{2}$$/gからAl$$_{2}$$O$$_{3}$$-5%Ti試料では982m$$^{2}$$/gまで大幅に増加した。これにより、Mo吸着量は、Al$$_{2}$$O$$_{3}$$で37.1mg/g、Al$$_{2}$$O$$_{3}$$-2.5%Tiで39.0mg/g、Al$$_{2}$$O$$_{3}$$-10%Tiで40.5mg/gであったが、Al$$_{2}$$O$$_{3}$$-5%Tiはよりも高い44.5mg/gを示した。これにより、従来のAl$$_{2}$$O$$_{3}$$の吸着能力と比較して、Al$$_{2}$$O$$_{3}$$-TiO$$_{2}$$複合材料の吸着能力の向上に見通しを得た。

論文

Fine structure in the $$alpha$$ decay of $$^{223}$$U

Sun, M. D.*; Liu, Z.*; Huang, T. H.*; Zhang, W. Q.*; Andreyev, A. N.; Ding, B.*; Wang, J. G.*; Liu, X. Y.*; Lu, H. Y.*; Hou, D. S.*; et al.

Physics Letters B, 800, p.135096_1 - 135096_5, 2020/01

https://doi.org/10.1016/j.physletb.2019.135096
 被引用回数：11 パーセンタイル：78.75(Astronomy & Astrophysics)

Fine structure in the $$alpha$$ decay of $$^{223}$$U was observed in the fusion-evaporation reaction $$^{187}$$Re($$^{40}$$Ar,p3n) by using fast digital pulse processing technique. Two $$alpha$$-decay branches of $$^{223}$$U feeding the ground state and 244 keV excited state of $$^{219}$$Th were identified by establishing the decay chain $$^{223}$$U$$rightarrow$$$$^{219}$$Th$$rightarrow$$$$^{215}$$Ra$$rightarrow$$$$^{211}$$Rn. The $$alpha$$-particle energy for the ground-state to ground-state transition of $$^{223}$$U was determined to be 8993(17) keV, 213 keV higher than the previous value, the half-life was updated to be 62$$^{+14}_{-10} mu$$s. Evolution of nuclear structure for $$N$$=131 even-$$Z$$ isotones from Po to U was discussed in the frameworks of nuclear mass and reduced $$alpha$$-decay width, a weakening octupole deformation in the ground state of $$^{223}$$U relative to its lighter isotones $$^{219}$$Ra and $$^{211}$$Th was suggested.

論文

Comparison of heavy-ion transport simulations; Collision integral with pions and $$Delta$$ resonances in a box

小野 章*; Xu, J.*; Colonna, M.*; Danielewicz, P.*; Ko, C. M.*; Tsang, M. B.*; Wang, Y,-J.*; Wolter, H.*; Zhang, Y.-X.*; Chen, L.-W.*; et al.

Physical Review C, 100(4), p.044617_1 - 044617_35, 2019/10

AA2019-0025.pdf:2.76MB

https://doi.org/10.1103/PhysRevC.100.044617
 被引用回数：60 パーセンタイル：98.59(Physics, Nuclear)

2017年4月に開催された国際会議Transport2017において、重イオン核反応モデルの国際的な比較が議論された。重イオン加速器の安全評価や宇宙飛行士の被ばく評価等で重要な役割を果たすため、世界中で重イオン核反応の様々な理論モデルが開発されている。本研究では、辺の長さが20fmの直方体に320個の中性子と陽子をランダム配置し、それらが70fm/cの間に起こす散乱の回数やエネルギーを計算した。ここでは、特にパイオンやその前駆体であるデルタ共鳴の生成に注目して比較を行った。参加コードは、個々の粒子の時間発展を追うQMD型コードと、粒子の位置や運動量の確率分布を決めておき、散乱や崩壊が発生したときそれらを乱数サンプリングするBUU型コードがあり、発表者が用いたJQMDは前者に属する。本研究により、計算における時間刻みが各コードによる結果の差の主な原因であることが分かった。さらに、今後のJQMDの改良方針の策定に有益な知見を得ることができた。

論文

Biomolecule-assisted synthesis of hierarchical multilayered boehmite and alumina nanosheets for enhanced molybdenum adsorption

Saptiama, I.*; Kaneti, Y. V.*; Yuliarto, B.*; 熊田 博明*; 土谷 邦彦; 藤田 善貴; Malgras, V.*; 福光 延吉*; 榮 武二*; 籏野 健太郎*; et al.

Chemistry; A European Journal, 25(18), p.4843 - 4855, 2019/03

https://doi.org/10.1002/chem.201900177
 被引用回数：15 パーセンタイル：54.71(Chemistry, Multidisciplinary)

ユニークな階層的多層構造を持つメソポーラスベーマイト($$gamma$$-AlOOH)およびガンマ-アルミナ($$gamma$$-Al$$_{2}$$O$$_{3}$$)ナノシート合成のために様々な生体分子の効果的な利用が実証されている。生体分子の性質と濃度は、得られる$$gamma$$-AlOOHおよび$$gamma$$-Al$$_{2}$$O$$_{3}$$ナノシートの結晶度,形態および組織特性に強く影響し、容易に調整可能である。生体分子を用いて合成された階層型$$gamma$$-AlOOHおよび$$gamma$$-Al$$_{2}$$O$$_{3}$$多層ナノシートは、生体分子なしで合成したものと比較して、結晶度の向上、粒子分離の改善および明確な多層構造を示した。さらに、これらの$$gamma$$-AlOOHおよび$$gamma$$-Al$$_{2}$$O$$_{3}$$ナノシートは、メソポーラス構造と階層的な多層構造により、それぞれ425, 371m$$^{2}$$/gの高い比表面積を有していた。医療用ラジオアイソトープ製造のためのモリブデン吸着材に適用した結果、階層型$$gamma$$-Al$$_{2}$$O$$_{3}$$多層ナノシートは33.1$$sim$$40.8mg-Mo/gのMo吸着容量を有した。このMo吸着性能は、結晶度,比表面積および細孔容積の相乗的な組合せによる影響を受ける。提案された生体分子支援合成方法は、将来、他の3Dメソポーラス酸化物の合成に発展する可能性がある。

論文

Comparison of heavy-ion transport simulations; Collision integral in a box

Zhang, Y.-X.*; Wang, Y,-J.*; Colonna, M.*; Danielewicz, P.*; 小野 章*; Tsang, M. B.*; Wolter, H.*; Xu, J.*; Chen, L.-W.*; Cozma, D.*; et al.

Physical Review C, 97(3), p.034625_1 - 034625_20, 2018/03

https://doi.org/10.1103/PhysRevC.97.034625
 被引用回数：100 パーセンタイル：99.11(Physics, Nuclear)

2017年4月に開催された国際会議Transport2017において、重イオン核反応モデルの国際的な比較が議論された。重イオン加速器の安全評価や宇宙飛行士の被ばく評価等で重要な役割を果たすため、世界中で重イオン核反応の様々な理論モデルが開発されている。本研究はモデル間の共通点と差異を明らかにし、各モデルの問題点を明らかにした。比較において、辺の長さが20fmの直方体に320個の中性子と320個の陽子をランダム配置し、それらが時間発展に伴って起こす散乱の回数や散乱時のエネルギーなどを計算する条件が設定された。また、結果以外にも、理論モデルを構成するアルゴリズムについても比較を行った。発表者は重イオン核反応モデルJQMD(JAERI Quantum Molecular Dynamics)を用いて計算を行い、世界で開発されている15の計算コードによる計算結果と比較した。コードアルゴリズムの比較では、JQMDは必ず陽子から 優先的に衝突確率を計算し、その後に中性子の衝突を計算するため、物理描像の妥当性が指摘された。一方、JQMDは他のモデルとほぼ同じ計算結果を出すことも判明した。衝突回数や運動量の計算値が平均から2倍以上乖離するモデルもある中で、JQMDは本計算条件で安定した性能を発揮することが確認された。

論文

Shell evolution beyond $$Z$$=28 and $$N$$=50; Spectroscopy of $$^{81,82,83,84}$$Zn

Shand, C. M.*; Podoly$'a$k, Zs.*; G$'o$rska, M.*; Doornenbal, P.*; Obertelli, A.*; Nowacki, F.*; Otsuka, T.*; Sieja, K.*; Tostevin, J. A.*; Tsunoda, T.*; et al.

Physics Letters B, 773, p.492 - 497, 2017/10

https://doi.org/10.1016/j.physletb.2017.09.001
 被引用回数：25 パーセンタイル：87.8(Astronomy & Astrophysics)

Low-lying states in neutron-rich $$^{81,82.83.84}$$Zn nuclei were measured for the first time via in-beam $$gamma$$-ray spectroscopy at RIKEN. These include the 4$$_1^+$$ to 2$$_1^+$$ in $$^{82}$$Zn and the 2$$_1^+$$ to 0$$_1^+$$ and 4$$_1^+$$ to 2$$_1^+$$ in $$^{84}$$Zn. The reduced E($$2^+$$) energies and increased E(4$$^+$$)/E(2$$^+$$) ratios at $$N$$=52,54 compared to $$^{80}$$Zn attest that the magicity is confined just on the neutron number $$N$$=50 only. The levels observed in $$^{84}$$Zn suggest the onset of deformation towards heavier Zn isotopes. The data were compared to state-of-the-art shell model calculations.

論文

Shape evolution in neutron-rich krypton isotopes beyond N=60; First spectroscopy of $$^{98,100}$$Kr

Flavigny, F.*; Doornenbal, P.*; Obertelli, A.*; Delaroche, J.-P.*; Girod, M.*; Libert, J.*; Rodriguez, T. R.*; Authelet, G.*; 馬場 秀忠*; Calvet, D.*; et al.

Physical Review Letters, 118(24), p.242501_1 - 242501_6, 2017/06

https://doi.org/10.1103/PhysRevLett.118.242501
 被引用回数：38 パーセンタイル：87.34(Physics, Multidisciplinary)

The first $$gamma$$-ray spectroscopy of very neutron rich $$^{98,100}$$Kr isotopes was carried out at the RIBF at RIKEN Nishina center. Excited states in these isotopes were populated via (p,2p) reactions using radioactive $$^{99,101}$$Rb beams accelerated to 220 MeV/nucleon. The new data show a significant increase in deformation beyond N=60, as well as competing configurations (shape-coexistence) at low energy. The data were compared with beyond-mean-field calculations which predict level energies in good agreement with observation, and suggest oblate-prolate shape coexistence.

論文

Low-lying structure and shape evolution in neutron-rich Se isotopes

Chen, S.*; Doornenbal, P.*; Obertelli, A.*; Rodriguez, T. R.*; Authelet, G.*; 馬場 秀忠*; Calvet, D.*; Ch$^a$teau, F.*; Corsi, A.*; Delbart, A.*; et al.

Physical Review C, 95(4), p.041302_1 - 041302_6, 2017/04

https://doi.org/10.1103/PhysRevC.95.041302
 被引用回数：26 パーセンタイル：88.47(Physics, Nuclear)

Neutron-rich isotopes of selenium, $$^{88,90,92,94}$$Se, where studied via in beam $$gamma$$-ray spectroscopy after nucleon removal reactions at RIBF in RIKEN. The low-energy excitations of these nuclei were investigated using $$gamma$$-$$gamma$$ coincidences, and the first and second excited 2$$^+$$ states were found at remarkably low energies. The analysis and comparison with self-consistent beyond-mean field calculations suggest that both shape coexistence and triaxiality are needed to describe these isotopes.

論文

Type II shell evolution in $$A=70$$ isobars from the $$N geq 40$$ island of inversion

Morales, A. I.*; Benzoni, G.*; Watanabe, H.*; 角田 佑介*; Otsuka, T.*; 西村 俊二*; Browne, F.*; Daido, R.*; Doornenbal, P.*; Fang, Y.*; et al.

Physics Letters B, 765, p.328 - 333, 2017/02

https://doi.org/10.1016/j.physletb.2016.12.025
 被引用回数：33 パーセンタイル：92.56(Astronomy & Astrophysics)

The level schemes of neutron-rich isotopes $$^{70}$$Co and $$^{70}$$Ni were populated in the $$beta$$ decay of $$^{70}$$Fe and studied using $$beta$$-delayed $$gamma$$-ray spectroscopy of the $$beta$$ decay, at the RIBF in RIKEN, Japan. The experimental results were compared to state-of-the-art shell-model calculations, and indicate a dominance of prolate deformation in the low-lying states, coexisting with spherical states. The $$beta$$ decay of the $$A=70$$ isobars is shown to progress in accordance to a new type of shell evolution, the so-called Type II, which involves many particle-hole excitations across energy gaps.

論文

Are there signatures of harmonic oscillator shells far from stability?; First spectroscopy of $$^{110}$$Zr

Paul, N.*; Corsi, A.*; Obertelli, A.*; Doornenbal, P.*; Authelet, G.*; 馬場 秀忠*; Bally, B.*; Bender, M.*; Calvet, D.*; Ch$^a$teau, F.*; et al.

Physical Review Letters, 118(3), p.032501_1 - 032501_7, 2017/01

https://doi.org/10.1103/PhysRevLett.118.032501
 被引用回数：44 パーセンタイル：89.18(Physics, Multidisciplinary)

The first measurement of $$gamma$$ rays emitted by the very neutron rich nuclei $$^{112}$$Mo (Z=42) and $$^{110}$$Zr (Z=40) was carried out at the RIBF facility at RIKEN. These data shine light on the postulated N=70 harmonic oscillator shell. If the spin-orbit splitting which gives rise to the N=82 shell gap is reduced in very neutron-rich nuclei, the harmonic oscillator gap at N=70 should open instead. However, both the measured energy of the first excited state $$^{112}$$Mo and $$^{110}$$Zr, respectively 235(7) keV and 185(11) keV, and their E(4$$^+$$)/E(2$$^+$$) ratio, indicate that these nuclei are good rotors, and exclude the shell stabilization scenario at Z=40 and N=70. These results were compared to state-of-the-art density functional theoretical calculations using Gogny and Skyrme effective interactions.

論文

Low-lying excitations in $$^{72}$$Ni

Morales, A. I.*; Benzoni, G.*; Watanabe, H.*; 西村 俊二*; Browne, F.*; Daido, R.*; Doornenbal, P.*; Fang, Y.*; Lorusso, G.*; Patel, Z.*; et al.

Physical Review C, 93(3), p.034328_1 - 034328_14, 2016/03

https://doi.org/10.1103/PhysRevC.93.034328
 被引用回数：25 パーセンタイル：84.88(Physics, Nuclear)

Low-lying excited states in $$^{72}$$Ni have been investigated at RIKEN by studying the $$beta$$ decay of $$^{72}$$Co to $$^{72}$$Ni. $$^{72}$$Co was separated with BigRIPS, implanted into the WaS3ABi Silicon array, and the $$gamma$$ ray measured using the EURICA $$gamma$$ spectrometer. From the analysis, 60 new $$gamma$$-ray transitions and 21 new levels in $$^{72}$$Ni were observed. The new experimental information is compared to shell-model calculations which include neutron excitation across the $$fpg$$ shell. The calculations reproduce rather well the observed states, implying that a clear understanding of these low-lying excitations has been achieved.

論文

Decay properties of $$^{68,69,70}$$Mn; Probing collectivity up to N=44 in Fe isotopic chain

Benzoni, G.*; Morales, A. I.*; Watanabe, H.*; 西村 俊二*; Coraggio, L.*; Itaco, N.*; Gargano, A.*; Browne, F.*; Daido, R.*; Doornenbal, P.*; et al.

Physics Letters B, 751, p.107 - 112, 2015/12

https://doi.org/10.1016/j.physletb.2015.10.025
 被引用回数：20 パーセンタイル：77.85(Astronomy & Astrophysics)

The $$beta$$ decays of $$^{68,69,70}$$Mn have been measured at the RIBF facility at RIKEN using the EURICA $$gamma$$ spectrometer combined with an active stopper consisting of a stack of Si detectors. Half-lives and $$beta$$-delayed neutron emission probabilities have been extracted for these decays, together with first experimental information on excited states populated in $$^{69,70}$$Fe. The data indicate a continuously increasing deformation for Fe isotopes up to A=70, and interpreted to be due to the interplay between quadrupole correlation of specific neutron orbitals and the monopole component of the proton-neutron interaction.

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