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論文

Spallation and fragmentation cross sections for 168 MeV/nucleon $$^{136}$$Xe ions on proton, deuteron, and carbon targets

Sun, X. H.*; Wang, H.*; 大津 秀暁*; 櫻井 博儀*; Ahn, D. S.*; 合川 正幸*; 福田 直樹*; 磯部 忠昭*; 川上 駿介*; 小山 俊平*; et al.

Physical Review C, 101(6), p.064623_1 - 064623_12, 2020/06

 被引用回数:2 パーセンタイル:35.83(Physics, Nuclear)

理化学研究所RIビームファクトリーにて逆運動学法を使用し、核子当たり168MeVの陽子, 重陽子, 炭素イオン入射による$$^{136}$$Xeのスポレーションおよびフラグメンテーション反応からの同位体生成断面積を測定した。炭素イオンの場合は全運動エネルギーが高くなるため、質量数の小さな同位体の生成断面積が大きくなった。また、今回新たに測定されたデータを以前により高い入射エネルギーで測定されたデータと比較することで、同位体生成断面積の入射エネルギー依存性を調査した。さらに、測定データをPHITS, SPACS, EPAX, DEURACSの計算値と比較した。本研究で測定したデータは、理論計算の良いベンチマークになると考えられる。

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:7 パーセンタイル:61.99(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:28 パーセンタイル:94.69(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:15 パーセンタイル:79.72(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:15 パーセンタイル:79.72(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:19 パーセンタイル:85.24(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

 被引用回数:18 パーセンタイル:81.47(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.

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:24 パーセンタイル:87.68(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:118 パーセンタイル:97.94(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:20 パーセンタイル:81.46(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

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:21 パーセンタイル:78.3(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:45 パーセンタイル:90.05(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.

論文

Muon spin rotation measurements of heterogeneous field response in overdoped La$$_{2-x}$$Sr$$_{x}$$CuO$$_{4}$$

MacDougall, G. J.*; Savici, A. T.*; Aczel, A. A.*; Birgeneau, R. J.*; Kim, H.*; Kim, S.-J.*; 伊藤 利充*; Rodriguez, J. A.*; Russo, P. L.*; 植村 泰朋*; et al.

Physical Review B, 81(1), p.014508_1 - 014508_7, 2010/01

 被引用回数:9 パーセンタイル:43.25(Materials Science, Multidisciplinary)

Transverse-field muon spin rotation measurements of overdoped La$$_{2-x}$$Sr$$_{x}$$CuO$$_{4}$$ reveal a large broadening of the local magnetic field distribution in response to applied field, persisting to high temperatures. The field response is approximately Curie-Weiss-like in temperature and is largest for the highest doping investigated. Such behavior is contrary to the canonical Fermi-liquid picture commonly associated with the overdoped cuprates and implies extensive heterogeneity in this region of the phase diagram. A possible explanation for the result lies in regions of staggered magnetization about dopant cations, analogous to what is argued to exist in underdoped systems.

論文

Absence of broken time-reversal symmetry in the pseudogap state of the high temperature La$$_{2-x}$$Sr$$_{x}$$CuO$$_{4}$$ superconductor from muon-spin-relaxation measurements

MacDougall, G. J.*; Aczel, A. A.*; Carlo, J. P.*; 伊藤 利充*; Rodriguez, J.*; Russo, P. L.*; 植村 泰朋*; 脇本 秀一; Luke, G. M.*

Physical Review Letters, 101(1), p.017001_1 - 017001_4, 2008/07

 被引用回数:60 パーセンタイル:89.38(Physics, Multidisciplinary)

銅酸化物高温超伝導体に見られる擬ギャップの起源として、擬ギャップ温度以下で、時間反転対称性の破れた軌道電流パターンを持つ秩序状態が存在することが理論で提唱され、YBCOを用いた中性子回折実験によりその軌道電流から生まれるモーメントに起因すると考えられる磁気ピークが観測されている。本研究では、微小な内部磁場の観測に優れるミュウオンスピン緩和測定を用いて、La$$_{2-x}$$Sr$$_{x}$$CuO$$_{4}$$の組成を最適ドープから過剰ドープまで変化させて軌道電流秩序状態があるかを検証した。その結果、軌道電流秩序状態はすべての組成で存在せず、仮に存在したとしても内部磁場にして0.2G以下であり、中性子で報告されたモーメントの200分の1以下となる。よって、理論で提唱されているような時間反転対称性の破れた軌道電流パターンを持つ秩序状態は存在しないことを示した。

論文

Muon spin rotation study of field-induced magnetism in heavily overdoped La$$_{2-x}$$Sr$$_{x}$$CuO$$_{4}$$

MacDougall, G. J.*; Birgeneau, R. J.*; Kim, H.*; Kim, S.-J.*; Rodriguez, J.*; Russo, P. L.*; Savici, A. T.*; 植村 泰朋*; 脇本 秀一; Wiebe, C. R.*; et al.

Physica B; Condensed Matter, 374-375, p.211 - 214, 2006/03

 被引用回数:4 パーセンタイル:23.8(Physics, Condensed Matter)

高温超伝導体の研究において、単結晶試料育成や化学的ドーピングの困難から、過剰ドープ領域の研究はほとんどなされていなかった。本研究では、世界初となる過剰ドープしたLa$$_{2-x}$$Sr$$_{x}$$CuO$$_{4}$$単結晶の$$mu$$SR実験の結果を報告する。縦磁場$$mu$$SRの結果から、relaxation rateの温度依存性がCurie-Weiss則に従い、そのCurie constantが磁場の関数として$$Cproptoalpha H$$と書かれることが見いだされた。この現象は、内部磁場分布の異常が磁場により誘起されていることを示している。磁場誘起の度合を表す$$alpha$$$$x=0.12$$から既に現れ、過剰ドープ領域の$$x=0.30$$まで単調増加し、ドープ量に依存することがわかった。この磁場誘起による異常な内部磁場分布の原因の解明は、今後の重要な課題である。

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