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論文

Two inherent crossovers of the diffusion process in glass-forming liquids

古府 麻衣子; Faraone, A.*; Tyagi, M.*; 長尾 道弘*; 山室 修*

Physical Review E, 98(4), p.042601_1 - 042601_6, 2018/10

 パーセンタイル:100(Physics, Fluids & Plasmas)

We report on incoherent quasielastic neutron scattering measurements examining a self-diffusion process in two types of glass-forming liquids, namely a molecular liquid (3-methylpentane) and an ionic liquid (1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide). We have experimentally demonstrated that both liquids exhibit two crossovers in the momentum transfer ($$Q$$) dependence of the self-correlation function, which is basically described by the stretched exponential function, $$exp [-(t/tau)^beta]$$. The first crossover point ($$Q approx 0.2$$~$AA$^{-1}$$) corresponds to a crossover from Fickian ($$beta = 1$$) to non-Fckian ($$beta ne 1$$) diffusion attributed to dynamical correlation. On the other hand, the second one at $$Q approx 0.8$$~$AA$^{-1}$$ is associated with the crossover from Gaussian to non-Gaussian behavior. It is remarkable that the stretching exponent $$beta$$ gradually changes in between the two crossover points. We consider that the two crossovers are the universal feature for glass-forming liquids.

論文

Observation of a $$gamma$$-decaying millisecond isomeric state in $$^{128}$$Cd$$_{80}$$

Jungclaus, A.*; Grawe, H.*; 西村 俊二*; Doornenbal, P.*; Lorusso, G.*; Simpson, G. S.*; S$"o$derstr$"o$m, P.-A.*; 炭竃 聡之*; Taprogge, J.*; Xu, Z. Y.*; et al.

Physics Letters B, 772, p.483 - 488, 2017/09

 被引用回数:4 パーセンタイル:30.79(Astronomy & Astrophysics)

A new high-spin isomer in the neutron-rich nucleus $$^{128}$$Cd was populated in the projectile fission of a $$^{238}$$U beam at the Radioactive Isotope Beam Factory at RIKEN. A half-life of T$$_{1/2}$$ = 6.3(8) ms was measured for the new state which was tentatively assigned a spin/parity of (15$$^-$$). The isomeric state decays via the emission of a 309-keV $$gamma$$ ray with $$E3$$ multipolarity. The experimental results are compared to shell model calculations performed using state-of-the-art realistic effective interactions and to the neighbouring nucleus $$^{129}$$Cd. The comparison with calculations shows that adjustments of the pairing and multipole parts of the effective interaction derived from the CD-Bonn nucleon-nucleon potential are required in order to describe the properties of nuclei in the region around $$^{132}$$Sn.

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

 被引用回数:10 パーセンタイル:8.11(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

$$beta$$ decay of semi-magic $$^{130}$$Cd; Revision and extension of the level scheme of $$^{130}$$In

Jungclaus, A.*; Grawe, H.*; 西村 俊二*; Doornenbal, P.*; Lorusso, G.*; Simpson, G. S.*; S$"o$derstr$"o$m, P. A.*; 炭竃 聡之*; Taprogge, J.*; Xu, Z. Y.*; et al.

Physical Review C, 94(2), p.024303_1 - 024303_8, 2016/08

 被引用回数:8 パーセンタイル:31.2(Physics, Nuclear)

The $$beta$$ decay of the semi-magic nucleus $$^{130}$$Cd has been studied at the RIBF facility at the RIKEN Nishina Center. The high statistics of the present experiment allowed for a revision of the established level scheme of $$^{130}$$In and the observation of additional $$beta$$ feeding to high lying core-excited states in $$^{130}$$In. The experimental results are compared to shell-model calculations employing a model space consisting of the full major $$N=50-82$$ neutron and $$Z=28-50$$ proton shells, and good agreement is found.

論文

First observation of $$gamma$$ rays emitted from excited states south-east of $$^{132}$$Sn; The $$pi$$ g$$_{9/2}^{-1}$$ $$ otimes$$ $$nu f_{7/2}$$ multiplet of $$^{132}$$In$$_{83}$$

Jungclaus, A.*; Gargano, A.*; Grawe, H.*; Taprogge, J.*; 西村 俊二*; Doornenbal, P.*; Lorusso, G.*; Shimizu, Y.*; Simpson, G. S.*; S$"o$derstr$"o$m, P.-A.*; et al.

Physical Review C, 93(4), p.041301_1 - 041301_6, 2016/04

 被引用回数:7 パーセンタイル:26.65(Physics, Nuclear)

For the first time, the decay of excited states in a nucleus situated "south-east" of $$^{132}$$Sn have been observed, in a region where experimental information is limited to ground-state properties. Six $$gamma$$ rays from $$^{133}$$Cd, produced in the fragmentation of a $$^{238}$$U beam at RIBF at RIKEN. The $$gamma$$ rays were studied using the EURICA array of Ge detectors. The new experimental information is compared to results from realistic shell-model calculations, which are the first in this region far from stability. Comparison with calculations suggests that at least four out of six new transitions can be attributed to the particle-hole configuration of one neutron in the $$f_{7/2}$$ and one proton hole in the $$g_{9/2}$$ orbits, respectively. This work constitutes an important first step towards the exploration of nuclear structure in this unknown region of the nuclear chart.

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

 被引用回数:11 パーセンタイル:14.96(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

$$beta$$ decay of $$^{129}$$Cd and excited states in $$^{129}$$In

Taprogge, J.*; Jungclaus, A.*; Grawe, H.*; 西村 俊二*; Doornenbal, P.*; Lorusso, G.*; Simpson, G. S.*; S$"o$derstr$"o$m, P.-A.*; 炭竃 聡之*; Xu, Z. Y.*; et al.

Physical Review C, 91(5), p.054324_1 - 054324_11, 2015/05

 被引用回数:15 パーセンタイル:13.65(Physics, Nuclear)

The $$beta$$ decay of $$^{129}$$Cd, produced in relativistic fission of a $$^{238}$$U beam, was studied at the RIKEN Nishina Center. From the $$gamma$$-ray analysis, 31 excited states and 69 $$gamma$$ ray transitions were established in the level scheme of $$^{129}$$In, and compared with state-of-the-art shell-model calculations. It was found that the $$beta$$ decay of $$^{129}$$Cd is dominated by Gamow teller transitions, but a non-negligible contribution to the $$beta$$ decay is also made by first-forbidden transitions. To estimate the contribution of first-forbidden transitions is important for calculations of the $$beta$$-decay half-lives of nuclei in this region.

論文

$$beta$$-decay half-lives of 110 neutron-rich nuclei across the $$N$$=82 shell gap; Implications for the mechanism and universality of the astrophysical $$r$$ process

Lorusso, G.*; 西村 俊二*; Xu, Z. Y.*; Jungclaus, A.*; Shimizu, Y.*; Simpson, G. S.*; S$"o$derstr$"o$m, P.-A.*; Watanabe, H.*; Browne, F.*; Doornenbal, P.*; et al.

Physical Review Letters, 114(19), p.192501_1 - 192501_7, 2015/05

 被引用回数:77 パーセンタイル:1.84(Physics, Multidisciplinary)

The $$beta$$-decay half-lives of 110 neutron-rich isotopes of the elements from Rb to Sn were measured at the RIBF Facility at RIKEN, Japan. The new data demonstrate the persistence of shell structure far from stability and have direct implications for the $$r$$-process calculations. In particular, the new half-lives have a global impact on the calculated $$r$$-process elemental abundances, and alleviate the underproduction of isotopes just above and below the A=130 peak, which in the past required the introduction of shell structure modifications. Reaction-network calculations based on the new data reinforce the notion that the r-process abundance pattern may result from the freeze-out of a (n,$$gamma$$)$$_leftarrow^{rightarrow}$$($$gamma$$,n) equilibrium.

論文

Identification of a millisecond isomeric state in $$^{129}$$Cd$$_{81}$$ via the detection of internal conversion and Compton electrons

Taprogge, J.*; Jungclaus, A.*; Grawe, H.*; 西村 俊二*; Xu, Z. Y.*; Doornenbal, P.*; Lorusso, G.*; N$'a$cher, E.*; Simpson, G. S.*; S$"o$derstr$"o$m, P.-A.*; et al.

Physics Letters B, 738, p.223 - 227, 2014/11

 被引用回数:14 パーセンタイル:19.65(Astronomy & Astrophysics)

The decay of an isomeric state in the neutron-rich nucleus $$^{129}$$Cd was observed via the detection of internal conversion and Compton electrons. This measurement provided the first experimental information on excited states in this nucleus. The isomer was populated in the projectile fission of a $$^{238}$$U beam at the RIBF facility at RIKEN. From the measured yields of $$gamma$$ rays and internal conversion electrons, E3 multipolarity was tentatively assigned to the isomeric transition. A half-life of 3.6(2) ms was determined for this new state which, by comparison with shell-model calculations, was tentatively assigned a spin of (21/2$$^+$$).

論文

Yrast 6$$^+$$ seniority isomers of $$^{136,138}$$Sn

Simpson, G. S.*; Gey, G.*; Jungclaus, A.*; Taprogge, J.*; 西村 俊二*; Sieja, K.*; Doornenbal, P.*; Lorusso, G.*; S$"o$derstr$"o$m, P.-A.*; 炭竃 聡之*; et al.

Physical Review Letters, 113(13), p.132502_1 - 132502_6, 2014/09

 被引用回数:39 パーセンタイル:7.38(Physics, Multidisciplinary)

Delayed $$gamma$$-ray cascades, originating from the decay of 6$$^+$$ isomeric states, in the very neutron-rich, semimagic isotopes $$^{136,138}$$Sn were observed following the projectile fission of a $$^{238}$$U beam at RIBF, RIKEN. The wave functions of these isomeric states are proposed to be predominantly a fully aligned pair of f$$_{7/2}$$ neutrons. Shell-model calculations, performed using a realistic effective interaction, reproduce well the energies of the excited states of these nuclei and the measured transition rates, with the exception of the $$B(E$$2;6$$^+ rightarrow 4^+$$) rate of $$^{136}$$Sn, which deviates from a simple seniority scheme. Empirically reducing the $$nu f$$$$_{7/2}^{2}$$ orbit matrix elements produces a 4+1 state with almost equal seniority 2 and 4 components, correctly reproducing the experimental $$B(E$$2;6$$^+ rightarrow 4^+$$) rate of $$^{136}$$Sn. These data provide a key benchmark for shell-model interactions far from stability.

論文

Monopole-driven shell evolution below the doubly magic nucleus $$^{132}$$Sn explored with the long-lived isomer in $$^{126}$$Pd

Watanabe, H.*; Lorusso, G.*; 西村 俊二*; Otsuka, T.*; Ogawa, K.*; Xu, Z. Y.*; 炭竃 聡之*; S$"o$derstr$"o$m, P.-A.*; Doornenbal, P.*; Li, Z.*; et al.

Physical Review Letters, 113(4), p.042502_1 - 042502_6, 2014/07

 被引用回数:13 パーセンタイル:26.29(Physics, Multidisciplinary)

A new isomer with a half-life of 23.0(8) ms has been identified in $$^{126}$$Pd at 2406 keV excitation. The proposed spin and parity configuration is 10$$^{+}$$, with maximally aligned configuration of two $$h$$$$_{11/2}$$ neutron hole. $$beta$$-decay from the long-lived isomer was also observed to populated excited states at high spins in $$^{126}$$Ag. The small energy difference between the 10$$^{+}$$ and 7$$^{-}$$ isomers in $$^{126}$$Pd was interpreted in the frame of the monopole shift of the 1$$h$$$$_{11/2}$$ neutron orbit. The effects of the monopole interaction on the evolution of single-neutron energies below $$^{132}$$Sn are discussed in terms of central and tensor forces.

論文

$$1p_{3/2}$$ proton-hole state in $$^{132}$$Sn and the shell structure along $$N$$=82

Taprogge, J.*; Jungclaus, A.*; Grawe, H.*; 西村 俊二*; Doornenbal, P.*; Lorusso, G.*; Simpson, G.*; S$"o$derstr$"o$m, P.-A.*; 炭竃 聡之*; Xu, Z. Y.*; et al.

Physical Review Letters, 112(13), p.132501_1 - 132501_6, 2014/04

 被引用回数:32 パーセンタイル:9.99(Physics, Multidisciplinary)

A low-lying state in $$^{131}$$In, the one-proton hole nucleus with respect to double magic $$^{132}$$Sn, was observed by its $$gamma$$ decay to the beta emitting isomer. The new state, which was populated both in the beta decay of $$^{131}$$Cd and after beta-delayed neutron emission from $$^{132}$$Cd, was identified, at an excitation energy of 1353 keV, as the previously unknown single-hole state with respect to the $$^{132}$$Sn core. Exploiting this crucial new experimental information, shell-model calculations were performed to study the structure of experimentally inaccessible $$N$$=82 isotones below $$^{132}$$Sn. The results evidence a surprising absence of proton subshell closures along the chain of $$N$$=82 isotones. This finding bears consequences on the evolution of the $$N$$=82 shell gap along the r-process path.

口頭

Spatial scale dependence of diffusion process in glass-forming liquids

古府 麻衣子; Faraone, A.*; Tyagi, M.*; 長尾 道弘*; 山室 修*

no journal, , 

液体中の分子の自己拡散はFickの法則に従うと考えられている。van Hoveの自己時空相関関数は空間$$r$$に対しガウス型、時間に対し指数関数で記述される(デバイ緩和)。この場合、緩和時間は$$tau propto Q^{-2}$$の関係式を満たす。しかしながら、ガラス形成液体の自己拡散は非デバイ型のKWW (Kohlrausch-Williams-Watts)関数、$$exp [-(t/tau)^{beta}]$$、で記述されることが多い。では、$$tau propto Q^{-2}$$の関係式は非デバイ型の拡散過程においても成り立つのだろうか?我々は、この問題に取り組むため、2種類の液体、分子液体(3メチルペンタン)とイオン液体(C4mimTFSI)の緩和時間の$$Q$$依存性を詳細に調べた。測定には、NISTに設置された中性子スピンエコー分光器、後方散乱分光器、チョッパー分光器の3台の装置を用いた。両方の液体において、2つのQ位置でクロスオーバーが観測された。1つ目のクロスオーバーは構造緩和とのカップリング、2つ目のクロスオーバーはガウス-非ガウス転移と考えられる。今回の結果は2つのクロスオーバーに関する初めての実験的証拠である。

口頭

ガラス形成液体における自己拡散過程の空間スケール依存性

古府 麻衣子; Faraone, A.*; Tyagi, M.*; 長尾 道弘*; 山室 修*

no journal, , 

液体中の自己拡散がFickの法則に従う場合、van Hoveの自己時空相関関数は空間$$r$$に対しガウス型、時間$$t$$に対し指数関数で記述される(デバイ緩和)。このとき、緩和時間$$tau$$$$Q^{-2}$$に比例する($$Q$$は散乱ベクトル)。しかしながら、多くのガラス形成液体の自己拡散は非デバイ型の伸長指数関数$$exp [-(t/tau)^{beta}]$$で記述され、$$tau propto Q^{-2}$$の関係は非自明である。これは、中性子散乱で観測する自己拡散とは何であるかという基本的な問いとも関連する。我々はこの問題に取り組むため、中性子準弾性散乱法を用い、2種類の液体について緩和挙動の$$Q$$依存性を詳細に調べた。試料は、分子液体である3-methylpentaneとイオン液体C4mimTFSIを選択した。2つの液体とも、緩和挙動が2つの$$Q$$位置($$Q_1 approx 0.2$$~$AA$^{-1}$$, $$Q_2 approx 0.8$$~$AA$^{-1}$$)で変化していることがわかった。$$Q_1$$での変化はFickの拡散から非Fick型の拡散へのクロスオーバーである。一方、$$Q_2$$でのクロスオーバーはガウス性の変化に関係すると考えられる。また、これらのクロスオーバー点で$$tau$$だけでなく$$beta$$も変化していることは興味深い。これらの振る舞いは2つの液体で同様であることから、この自己拡散挙動がガラス形成液体に普遍的なものであることを示唆している。

口頭

Dynamics of atomic hydrogen in bulk and nanocrystalline palladium

古府 麻衣子; 橋本 直樹*; 秋葉 宙*; 小林 浩和*; 北川 宏*; Tyagi, M.*; Faraone, A.*; Copley, J.*; Lohstorh, W.*; 飯田 一樹*; et al.

no journal, , 

パラジウム水素化物は代表的な金属水素化物であり、高い水素吸蔵性とパラジウム格子中の水素原子の高い拡散性などの特長をもつ。金属をナノ粒子化すると、表面効果や量子効果などにより物性が変わることが報告され、近年盛んに研究されている。中性子散乱手法は、金属中の水素原子を捉えるのに最も適したプローブである。我々は、パラジウム水素化物ナノ粒子の特性を明らかにするため、中性子回折, 中性子準弾性, 中性子非弾性散乱測定を行い、水素原子の配置, 拡散および振動挙動を調べた。その結果、ナノ粒子の表面付近では、水素原子はバルクとは異なる四面体サイトにも存在し(バルク試料では八面体サイトにのみ存在する)、速く拡散していることがわかった。また振動励起の解析から、表面付近の水素原子周りのポテンシャルは非調和性が大きいことも明らかにした。講演では、バルク試料で新たに検知された速い拡散についても報告し、過去の結果との比較を行う。

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