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Shell evolution of $$N$$ = 40 isotones towards $$^{60}$$Ca; First spectroscopy of $$^{62}$$Ti

Cort$'e$s, M. L.*; Rodriguez, W.*; Doornenbal, P.*; Obertelli, A.*; Holt, J. D.*; Lenzi, S. M.*; Men$'e$ndez, J.*; Nowacki, F.*; 緒方 一介*; Poves, A.*; et al.

Physics Letters B, 800, p.135071_1 - 135071_7, 2020/01

 被引用回数:3 パーセンタイル:13.44(Astronomy & Astrophysics)

ガンマ線分光による$$N$$=40同調体である$$^{62}$$Tiの分光学研究を$$^{63}$$V($$p$$,$$2p$$)$$^{62}$$TiをRIBFで行った。今回初めて測定された$$2_1^+ rightarrow 0_{rm gs}^+$$$$4_1^+ rightarrow 2_1^+$$の遷移はTiの基底状態が変形していることを示唆した。これらのエネルギーは近傍核の$$^{64}$$Crや$$^{66}$$Feと比較して大きく、したがって四重極集団運動が小さくなっていることが示唆される。今回の結果は大規模殻模型計算によって良く再現される一方、第一原理計算や平均場模型では今回の結果は再現されなかった。


Quasifree neutron knockout from $$^{54}$$Ca corroborates arising $$N=34$$ neutron magic number

Chen, S.*; Lee, J.*; Doornenbal, P.*; Obertelli, A.*; Barbieri, C.*; 茶園 亮樹*; Navr$'a$til, P.*; 緒方 一介*; 大塚 孝治*; Raimondi, F.*; et al.

Physical Review Letters, 123(14), p.142501_1 - 142501_7, 2019/10

 被引用回数:8 パーセンタイル:16.18(Physics, Multidisciplinary)

$$^{54}$$Caでは中性子魔法数34が現れると考えられているが、その直接的な実験的証拠を得るため、$$^{54}$$Caからの中性子ノックアウト反応$$^{54}$$Ca($$p,pn$$)$$^{53}$$Caによって生成される状態を理化学研究所のRI Beam Factoryによって調べた。基底状態および2.2MeVの励起状態が強く生成され、1.7MeVの励起状態の生成量は小さかった。$$^{53}$$Caの運動量分布から、基底状態および2.2MeVの励起状態は$$p$$軌道の中性子を叩き出して得られた状態であることが明らかになった。DWIA計算によって得られた分光学的因子から、$$^{54}$$Caは$$p$$軌道がほぼ完全に占有された閉殻構造を持つことが明らかになり、中性子魔法数34の出現が確実なものとなった。


Nuclear structure of $$^{76}$$Ni from the ($$p$$,$$2p$$) reaction

Elekes, Z.*; Kripk$'o$, $'A$*; Sohler, D.*; Sieja, K.*; 緒方 一介*; 吉田 数貴; Doornenbal, P.*; Obertelli, A.*; Authelet, G.*; 馬場 秀忠*; et al.

Physical Review C, 99(1), p.014312_1 - 014312_7, 2019/01

 被引用回数:3 パーセンタイル:27.46(Physics, Nuclear)

($$p$$,$$2p$$)反応による$$^{76}$$Niの核構造の探索実験を行った。Lenzi, Nowacki, Poves, Sieja相互作用を用いた殻模型計算では実験結果を説明しうる陽子空孔状態が得られており、理論的な断面積計算は実験値とよい一致を与えた。実験で得られたすべての状態を理論的に一意に決定することはできなかったが、過去の実験結果と同様にNi同位体でのZ = 28の大きなshell gapを示す結果が得られた。


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

 被引用回数:13 パーセンタイル:13.18(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.


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

 被引用回数:21 パーセンタイル:11.07(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.


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

 被引用回数:15 パーセンタイル:10.36(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.


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

 被引用回数:23 パーセンタイル:9.8(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.


Fast-timing study of the $$l$$-forbidden 1/2$$^+$$ $$rightarrow$$ 3/2$$^+$$ $$M1$$ transition in $$^{129}$$Sn

Lic$u{a}$, R.*; Mach, H.*; Fraile, L. M.*; Gargano, A.*; Borge, M. J. G.*; M$u{a}$rginean, N.*; Sotty, C. O.*; Vedia, V.*; Andreyev, A.; Benzoni, G.*; et al.

Physical Review C, 93(4), p.044303_1 - 044303_7, 2016/04

 被引用回数:5 パーセンタイル:48.22(Physics, Nuclear)

The levels in $$^{129}$$Sn populated from the $$beta^-$$ decay of $$^{129}$$In isomers were investigated at the ISOLDE facility of CERN using the newly commissioned ISOLDE Decay Station. The lowest 1/2$$^+$$ state and the 3/2$$^+$$ ground state in $$^{129}$$Sn are expected to have configurations dominated by the neutron $$s_{1/2}$$ ($$l$$=0) and $$d_{3/2}$$ ($$l$$=2) single-particle states, respectively. Consequently, these states should be connected by a somewhat slow $$l$$-forbidden $$M1$$ transition. Using fast-timing spectroscopy we have measured the half-life of the 1/2$$^+$$ 315.3-keV state, $$T_{1/2}$$ = 19(10) ps, which corresponds to a moderately fast $$M1$$ transition. Shell-model calculations using the CD-Bonn effective interaction, with standard effective charges and $$g$$ factors, predict a 4-ns half-life for this level. We can reconcile the shell-model calculations to the measured $$T_{1/2}$$ value by the renormalization of the $$M1$$ effective operator for neutron holes.


Cluster-transfer reactions with radioactive beams; A Spectroscopic tool for neutron-rich nuclei

Bottoni, S.*; Leoni, S.*; Fornal, B.*; Raabe, R.*; Rusek, K.*; Benzoni, G.*; Bracco, A.*; Crespi, F. C. L.*; Morales, A. I.*; Bednarczyk, P.*; et al.

Physical Review C, 92(2), p.024322_1 - 024322_8, 2015/08

 被引用回数:14 パーセンタイル:21.8(Physics, Nuclear)

An exploratory experiment was performed at REX-ISOLDE CERN to test the potential of cluster-transfer reactions at the Coulomb barrier as a mechanism to explore the structure of exotic neutron-rich nuclei. The transfer of triton and alpha particles in a reaction of a beam of $$^{98}$$Rb onto a $$^7$$Li target were studied through particle-$$gamma$$ coincidence measurements. The results indicate that such cluster transfer reactions can be an efficient method to investigate the structure of neutron-rich nuclei at medium-high excitation energies and spins.


Experimental study of the $$^{66}$$Ni($$d$$,$$p$$)$$^{67}$$Ni one-neutron transfer reaction

Diriken, J.*; Patronis, N.*; Andreyev, A.; Antalic, S.*; Bildstein, V.*; Blazhev, A.*; Darby, I. G.*; De Witte, H.*; Eberth, J.*; Elseviers, J.*; et al.

Physical Review C, 91(5), p.054321_1 - 054321_15, 2015/05

 被引用回数:8 パーセンタイル:38.21(Physics, Nuclear)

Excited states up to an excitation energy of 5.8 MeV were populated in the neutron-rich isotope $$^{67}$$Ni via the $$^{66}$$Ni(d,p) transfer reaction at REX-Isolde, CERN. In particular, single-neutron states above the N=40 sub-shell gap were populated, and the relative spectroscopic factors were extracted using distorted-wave Born approximation analysis. The positive parity g$$_{9/2}$$, d$$_{5/2}$$ and s$$_{1/2}$$ neutron orbits above the shell closure are assumed to induce strong quadrupole collectivity in neutron-rich Fe and Cr isotopes. The extracted relative spectroscopic factors show that the strength of the d$$_{5/2}$$ orbit is mostly split over two states, hinting to substantial mixing of the neutron d$$_{5/2}$$ configuration with collective modes of the core. The size of the N=50 shell gap was also estimated, and found to be 2.6 MeV near $$^{68}$$Ni, as also determined in lighter Ni isotopes.


$$^{12}$$C + p resonant elastic scattering in the Maya active target

Sambi, S.*; Raabe, R.*; Borge, M. J. G.*; Caamano, M.*; Damoy, S.*; Fern$'a$ndez-Dom$'i$nguez, B.*; Flavigny, F.*; Fynbo, H.*; Gibelin, J.*; Grinyer, G. F.*; et al.

European Physical Journal A, 51(3), p.25_1 - 25_7, 2015/03

 被引用回数:5 パーセンタイル:53.41(Physics, Nuclear)

In a proof-of-principle experiment, the Maya active target detector was employed to study the $$^{12}$$C(p,p) resonant elastic scattering reaction in inverse kinematics. The excitation energy region from 0 to 3 MeV above the proton-breakup threshold in $$^{13}$$N was investigated in a single experiment. The excitation spectrum of $$^{13}$$N was fitted using R-matrix formalism. The level parameters extracted are in good agreement with previous studies. The active target proved its potential for the study of resonant elastic scattering in inverse kinematics with radioactive beams, when detection efficiency is of primary importance.


Single-neutron orbits near $$^{78}$$Ni; Spectroscopy of the N=49 isotope $$^{79}$$Zn

Orlandi, R.; M$"u$cher, D.*; Raabe, R.*; Jungclaus, A.*; Pain, S. D.*; Bildstein, V.*; Chapman, R.*; de Angelis, G.*; Johansen, J. G.*; Van Duppen, P.*; et al.

Physics Letters B, 740, p.298 - 302, 2015/01

 被引用回数:19 パーセンタイル:14.17(Astronomy & Astrophysics)

Single-neutron states in $$^{79}$$Zn have been populated using the reaction $$^{78}$$Zn(d,p) at REX-Isolde, CERN. The analysis reveals that the lowest excited states in $$^{79}$$Zn lie at approximately 1 MeV, and involve neutron orbits above the N=50 shell gap. A 5/2$$^{+}$$ configuration was assigned to the 983-keV state. Comparison with large-scale shell model calculations supports a robust neutron N=50 shell closure for $$^{78}$$Ni. These data constitute an important step towards the understanding the magicity of $$^{78}$$Ni and the structure of nuclei in the region.


Study of the deformation-driving $$nu$$d$$_{5/2}$$ orbital in $$_{28}^{67}$$Ni$$_{39}$$ using one-neutron transfer reactions

Diriken, J.*; Patronis, N.*; Andreyev, A. N.*; Antalic, S.*; Bildstein, V.*; Blazhev, A.*; Darby, I. G.*; De Witte, H.*; Eberth, J.*; Elseviers, J.*; et al.

Physics Letters B, 736, p.533 - 538, 2014/09

 被引用回数:12 パーセンタイル:29.27(Astronomy & Astrophysics)

The neutron orbits $$g_{9/2}$$, d$$_{5/2}$$ and s$$_{1/2}$$ are assumed to be responsible for the swift onset of collectivity observed in the region below $$^{68}$$Ni. In order to gather information on the single-particle energies and spectroscopic factors of these orbitals, single-particle states in the nucleus $$^{67}$$Ni were populated using the reaction $$^{66}$$Ni(d,p), in inverse kinematics, at REX-ISOLDE, CERN. The new isotope was studied using combined particle-$$gamma$$ spectroscopy. Comparison with DWBA calculations, permitted the identification of positive parity states with a substantial amount of $$nu$$d$$_{9/2}$$ (1007 keV) and $$nu$$d$$_{5/2}$$ (2207 and 3277 keV) single-particle strength. Comparisons with extended Shell-Model calculations was also performed to confirm the single-particle nature of these states, and to deduce general properties around $$^{68}$$Ni.


Limited asymmetry dependence of correlations from single nucleon transfer

Flavigny, F.*; Gillibert, A.*; Nalpas, L.*; Obertelli, A.*; Keeley, N.*; Barbieri, C.*; Beaumel, D.*; Boissinot, S.*; Burgunder, G.*; Cipollone, A.*; et al.

Physical Review Letters, 110(12), p.122503_1 - 122503_5, 2013/03

 被引用回数:50 パーセンタイル:8.84(Physics, Multidisciplinary)

陽子や中性子が過剰ないわゆるエキゾチック核の一粒子的性質などを調べるために、直接反応は有力な手法として知られている。入射エキゾチック核から陽子や中性子を1, 2個叩き出す、ノックアウト反応から導き出された分光学的因子は、殻模型によるものに比べて減少していることが知られ、また、その減少の因子は入射核の陽子/中性子比に強く依存するとされてきた。この研究では、フランスGANILで$$^{14}$$Oの核子移行反応を行い、そこから分光学的因子を得た。その結果、減少因子は、ノックアウト反応ほどは陽子/中性子比に強く依存しないとがわかった。これまで、核構造の観点から減少因子を理解しようとされてきたが、この研究により、反応機構にも大きな不定性があることが示された。


Low-energy states in $$^{79}$$Zn and the structure of $$^{78}$$Ni

Orlandi, R.; M$"u$cher, D.*; Raabe, R.*; Jungclaus, A.*; Pain, S. D.*; Bildstein, V.*; Chapman, R.*; de Angelis, G.*; Johansen, J. G.*; Van Duppen, P.*; et al.

no journal, , 

Single-neutron states in the $$N$$ = 49 isotope $$^{79}$$Zn were populated in the $$^{78}$$Zn(d,p)$$^{79}$$Zn transfer reaction at REX-ISOLDE, CERN. The combined detection of protons ejected in the reaction and of $$gamma$$ rays emitted by $$^{79}$$Zn permitted the identification of the lowest-lying 5/2$$^+$$ and 1/2$$^+$$ excited states. The analysis of proton angular distributions links these states to a significant amount of single-particle strength around 1 MeV, and specifically to the $$nu$$d$$_{5/2}$$ and $$nu$$s$$_{1/2}$$ neutron orbits, which lie above the $$N$$ = 50 neutron shell gap. Comparison with large-scale-shell-model calculations supports a robust $$N$$ = 50 shell-closure for $$^{78}$$Ni. These data constitute a considerable step towards the understanding of the magicity of $$^{78}$$Ni and of the structure of isotopes in the region.

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