| 1. |
- Aktas, Özge, 1987-, et al.
(author)
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First observation of γ-ray transitions in 111Mo
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In: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X.
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Journal article (peer-reviewed)abstract
- Excited states in the extremely neutron-rich nuclei 109Mo and 111Mo have been studied following nucleon knock-out reactions. Seven $\gamma$-ray transitions, some of them in prompt mutual coincidence, have been identified for the first time in 11Mo using the DALI2 and MINOS detector systems at the BigRIPS and ZeroDegree electromagnetic fragments separator at the RIBF, RIKEN, Japan. Total Routhian surface (TRS) and Particle- Plus Rotor calculations have been performed to investigate the predicted shape coexistence and its effect on the structure of nuclei in this region of the nuclear chart. Following the results of the calculations, theoretical level schemes are proposed for positive and negative parity states and compared with the experimental findings.
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| 2. |
- Aktas, Özge, et al.
(author)
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Single-particle structures in 85,87Ge
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In: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X.
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Journal article (peer-reviewed)abstract
- Gamma-ray transitions have been identified for the first time in the extremely neutron-rich (N =Z + 25) nucleus 87 Ge following nucleon knockout reactions studied at the RIBF, RIKEN, Japan.New γ-ray transitions from excited states in 85 Ge were also observed and placed in a tentative levelscheme. The exclusive parallel momentum distribution was measured for the 1/2 + state for theneutron knockout reaction leading to 85 Ge which is compared with calculated distorted wave impulseapproximation (DWIA) distributions. The 85,87 Ge results are compared with large-scale shell-modelcalculations and potential energy surface calculations based on the total Routhian surface formalism.
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| 3. |
- Petrache, C. M., et al.
(author)
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Collective rotation of an oblate nucleus at very high spin
- 2019
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In: Physical Review C. - : American Physical Society (APS). - 2469-9985 .- 2469-9993. ; 99:4
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Journal article (peer-reviewed)abstract
- A sequence of nine almost equidistant quadrupole transitions is observed in Nd137. The sequence represents an extremely regular rotational band that extends to a spin of about 75/2 and an excitation energy of ≈4.5MeV above yrast. Cranked mean-field calculations of the Nilsson-Strutinsky type suggest an oblate shape for the band. They reproduce the observed I(I+1) dependence of the rotational energy whereas predicting a pronounced decrease in the deformation, which is the hallmark of antimagnetic rotation.
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| 4. |
- Chen, S., et al.
(author)
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Level structures of 56,58Ca cast doubt on a doubly magic 60Ca
- 2023
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In: Physics Letters B. - : Elsevier B.V.. - 0370-2693 .- 1873-2445. ; 843
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Journal article (peer-reviewed)abstract
- Gamma decays were observed in 56Ca and 58Ca following quasi-free one-proton knockout reactions from 57,59Sc beams at ≈200 MeV/nucleon. For 56Ca, a γ ray transition was measured to be 1456(12) keV, while for 58Ca an indication for a transition was observed at 1115(34) keV. Both transitions were tentatively assigned as the 21+→0gs+ decays, and were compared to results from ab initio and conventional shell-model approaches. A shell-model calculation in a wide model space with a marginally modified effective nucleon-nucleon interaction depicts excellent agreement with experiment for 21+ level energies, two-neutron separation energies, and reaction cross sections, corroborating the formation of a new nuclear shell above the N = 34 shell. Its constituents, the 0f5/2 and 0g9/2 orbitals, are almost degenerate. This degeneracy precludes the possibility for a doubly magic 60Ca and potentially drives the dripline of Ca isotopes to 70Ca or even beyond.
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| 5. |
- Juhasz, M. M., et al.
(author)
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First spectroscopic study of( 51)Ar by the (p,2p) reaction
- 2021
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In: Physics Letters B. - : ELSEVIER. - 0370-2693 .- 1873-2445. ; 814
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Journal article (peer-reviewed)abstract
- The nuclear structure of Ar-51, an uncharted territory so far, was studied by the (p,2p) reaction using gamma-ray spectroscopy for the bound states and the invariant mass method for the unbound states. Two peaks were detected in the gamma-ray spectrum and six peaks were observed in the Ar-50+n relative energy spectrum. Comparing the results to our shell-model calculations, two bound and six unbound states were established. Three of the unbound states could only be placed tentatively due to the low number of counts in the relative energy spectrum of events associated with the decay through the first excited state of Ar-50. The low cross sections populating the two bound states of Ar-51 could be interpreted as a clear signature for the presence of significant subshell closures at neutron numbers 32 and 34 in argon isotopes. It was also revealed that due to the two valence holes, unbound collective states coexist with individual-particle states in Ar-51.
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| 6. |
- Koiwai, T., et al.
(author)
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A first glimpse at the shell structure beyond Ca-54 : Spectroscopy of K-55, Ca-55, and Ca-57
- 2022
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In: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 827, s. 136953-
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Journal article (peer-reviewed)abstract
- States in the N = 35 and 37 isotopes Ca-55,Ca-57 have been populated by direct proton-induced nucleon removal reactions from Sc-56,Sc-58 and Ca-56 beams at the RIBF. In addition, the (p, 2p) quasi-free single-proton removal reaction from Ca-56 was studied. Excited states in K-55, Ca-55, and Ca-57 were established for the first time via in-beam gamma-ray spectroscopy. Results for the proton and neutron removal reactions from Ca-56 to states in K-55 and Ca-55 for the level energies, excited state lifetimes, and exclusive cross sections agree well with state-of-the-art theoretical calculations using different approaches. The observation of a short-lived state in Ca-57 suggests a transition in the calcium isotopic chain from single-particle dominated states at N = 35 to collective excitations at N = 37.
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| 7. |
- Liu, Hongna, et al.
(author)
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How Robust is the N=34 Subshell Closure? : First Spectroscopy of Ar-52
- 2019
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In: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 122:7
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Journal article (peer-reviewed)abstract
- The first gamma-ray spectroscopy of Ar-52, with the neutron number N = 34, was measured using the K-53(p, 2p) one-proton removal reaction at similar to 210 MeV/u at the RIBF facility. The 2(1)(+) excitation energy is found at 1656(18) keV, the highest among the Ar isotopes with N > 20. This result is the first experimental signature of the persistence of the N = 34 subshell closure beyond Ca-54, i.e., below the magic proton number Z = 20. Shell-model calculations with phenomenological and chiral-effective-field-theory interactions both reproduce the measured 2(1)(+) systematics of neutron-rich Ar isotopes, and support a N = 34 subshell closure in Ar-52.
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| 8. |
- Zhang, Wei, et al.
(author)
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Lifetime measurements of excited states in 169,171,173Os : Persistence of anomalous B(E2) ratios in transitional rare earth nuclei in the presence of a decoupled i13/2 valence neutron
- 2021
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In: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 820
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Journal article (peer-reviewed)abstract
- Lifetimes of low-lying excited states in the νi13/2+ bands of the neutron-deficient osmium isotopes 169,171,173Os have been measured for the first time using the recoil-distance Doppler shift and recoil-isomer tagging techniques. An unusually low value is observed for the ratio B(E2;21/2+→17/2+)/B(E2;17/2+→13/2+) in 169Os, similar to the “anomalously” low values of the ratio B(E2;41+→21+)/B(E2;21+→0gs+) previously observed in several transitional rare-earth nuclides with even numbers of neutrons and protons, including the neighbouring 168,170Os. Furthermore, the evolution of B(E2;21/2+→17/2+)/B(E2;17/2+→13/2+) with increasing neutron number in the odd-mass isotopic chain 169,171,173Os is observed to follow the same trend as observed previously in the even-even Os isotopes. These findings indicate that the possible quantum phase transition from a seniority conserving structure to a collective regime as a function of neutron number suggested for the even-even systems is maintained in these odd-mass osmium nuclei, with the odd valence neutron merely acting as a “spectator”. As for the even-even nuclei, the phenomenon is highly unexpected for nuclei that are not situated near closed shells.
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