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1.
  • Aktas, Özge, 1987-, et al. (författare)
  • First observation of γ-ray transitions in 111Mo
  • Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X.
  • Tidskriftsartikel (refereegranskat)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 (författare)
  • Gamma-ray Spectroscopy ofNeutron-rich 111 Mo, 85,87 Ge andSelf-Conjugate 88 Ru Far From Stability
  • 2021
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • The neutron-deficient self-conjugate (N=Z) nucleus 8844 Ru 44 was populatedvia the heavy ion fusion evaporation reaction 54 Fe( 36 Ar, 2n) 88 Ru in an ex-periment performed at the GANIL accelerator laboratory in France. Usingthe AGATA γ-ray spectrometer together with ancillary detectors, promptγ − γ − 2n coincidence and charge particle anticoincidence analysis was per-formed for the low-lying energy spectrum of 88 Ru. The results confirm thepreviously assigned γ-ray cascade and extend it to the 14 + level. The levelscheme is consistent with a deformed rotational system. However, the rota-tional frequency of the alignment of the valence nucleons has a significantlyhigher value than what is predicted by theoretical calculations performedwithout isoscalar neutron-proton pairing. By including isoscalar pairing, anagrement is obtained with the experimentally observed delayed rotationalalignment.Excited states in the neutron-rich nuclei 109 Mo and 111 Mo were studiedfollowing nucleon knock-out reactions. Seven γ-ray transitions, some of themin prompt mutual coincidence, were identified for the first time in 111 Mo usingthe DALI2 and MINOS detector systems at the BigRIPS and ZeroDegree elec-tromagnetic fragment separator at the RIBF, RIKEN, Japan. Total Routhiansurface (TRS) and Particle-Plus-Rotor calculations have been performed toinvestigate the predicted shape coexistence and its effect on the structure ofnuclei in this region of the nuclear chart. Following the results of the calcula-tions, theoretical level schemes are proposed for positive and negative paritystates and compared with the experimental findings.Gamma-ray transitions have been identified for the first time in the ex-tremely neutron-rich (N = Z + 25) nucleus 87 Ge following nucleon knockoutreactions studied at the RIBF, RIKEN, Japan. Previously unknown γ-raytransitions between excited states in 85 Ge were also observed and placed ina tentative level scheme. The results are compared with large-scale shell-model calculations and potential energy surface calculations based on thetotal Routhian surface formalism. The neutron-rich titanium isotopes havebeen studied, and preliminary results are presented in this work. For the odd-even 57,59,61 Ti isotopes several gamma-ray transitions has been identified forthe first time. For the even-even isotopes 56,58,60 Ti the previously knowndecays from 2 + and 4 + spin-parity states, are confirmed with the currentpreliminary analysis.
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3.
  • Aktas, Özge, et al. (författare)
  • Single-particle structures in 85,87Ge
  • Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X.
  • Tidskriftsartikel (refereegranskat)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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4.
  • Browne, F., et al. (författare)
  • Pairing Forces Govern Population of Doubly Magic Ca-54 from Direct Reactions
  • 2021
  • Ingår i: Physical Review Letters. - : American Physical Society (APS). - 0031-9007 .- 1079-7114. ; 126:25
  • Tidskriftsartikel (refereegranskat)abstract
    • Direct proton-knockout reactions of Sc-55 at similar to 220 MeV/nucleon were studied at the RIKEN Radioactive Isotope Beam Factory. Populated states of Ca-54 were investigated through -ray and invariant-mass spectroscopy. Level energies were calculated from the nuclear shell model employing a phenomenological intemucleon interaction. Theoretical cross sections to states were calculated from distorted-wave impulse approximation estimates multiplied by the shell model spectroscopic factors, which describe the wave function overlap of the Sc-55 ground state with states in Ca-54. Despite the calculations showing a significant amplitude of excited neutron configurations in the ground-state of Sc-55, valence proton removals populated predominantly the ground state of Ca-54. This counterintuitive result is attributed to pairing effects leading to a dominance of the ground-state spectroscopic factor. Owing to the ubiquity of the pairing interaction, this argument should be generally applicable to direct knockout reactions from odd-even to even-even nuclei.
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5.
  • Cederwall, Bo, 1964-, et al. (författare)
  • Isospin Properties of Nuclear Pair Correlations from the Level Structure of the Self-Conjugate Nucleus Ru 88
  • 2020
  • Ingår i: Physical Review Letters. - : American Physical Society (APS). - 0031-9007 .- 1079-7114. ; 124:6
  • Tidskriftsartikel (refereegranskat)abstract
    • The low-lying energy spectrum of the extremely neutron-deficient self-conjugate (N = Z) nuclide 88Ru has been measured using the combination of the Advanced Gamma Tracking Array (AGATA)spectrometer, the NEDA, and Neutron Wall neutron detector arrays, and the DIAMANT charged particle detector array. Excited states in 88 Ru were populated via the 54 Feð 36 Ar; 2nγÞ 88 Ru fusion-evaporationreaction at the Grand Accélérateur National d’Ions Lourds (GANIL) accelerator complex. The observed γ-ray cascade is assigned to 88 Ru using clean prompt γ-γ-2-neutron coincidences in anticoincidence with the detection of charged particles, confirming and extending the previously assigned sequence of low-lying excited states. It is consistent with a moderately deformed rotating system exhibiting a band crossing at a rotational frequency that is significantly higher than standard theoretical predictions with isovector pairing, as well as observations in neighboring N > Z nuclides. The direct observation of such a “delayed” rotational alignment in a deformed N 1⁄4 Z nucleus is in agreement with theoretical predictions related to the presence of strong isoscalar neutron-proton pair correlations.
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6.
  • Cederwall, Bo, 1964-, et al. (författare)
  • Lifetime Measurements of Excited States in Pt-172 and the Variation of Quadrupole Transition Strength with Angular Momentum
  • 2018
  • Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 121:2
  • Tidskriftsartikel (refereegranskat)abstract
    • Lifetimes of the first excited 2(+) and 4(+) states in the extremely neutron -deficient nuclide Pt-172 have been measured for the first time using the recoil-distance Doppler shift and recoil-decay tagging techniques. An unusually low value of the ratio B(E2: 4(1)(+) -> 2(1)(+)/B(E2: 2(1)(+) -> 0(gs)(+)) = 0.55(19) was found, similar to a handful of other such anomalous cases observed in the entire Segre chart. The observation adds to a cluster of a few extremely neutron -deficient nuclides of the heavy transition metals with neutron numbers N approximate to 90-94 featuring the effect. No theoretical model calculations reported to date have been able to explain the anomalously low B(E2: 4(1)(+) -> 2(1)(+)/B(E2: 2(1)(+) -> 0(gs)(+)) ratios observed in these cases. Such low values cannot, e.g., be explained within the framework of the geometrical collective model or by algebraic approaches within the interacting boson model framework. It is proposed that the group of B(E2: 4(1)(+) -> 2(1)(+)/B(E2: 2(1)(+) -> 0(gs)(+)) ratios in the extremely neutron-deficient even-even W, Os, and Pt nuclei around neutron numbers N approximate to 90-94 reveal a quantum phase transition from a seniority-conserving structure to a collective regime as a function of neutron number. Although a system governed by seniority symmetry is the only theoretical framework for which such an effect may naturally occur, the phenomenon is highly unexpected for these nuclei that are not situated near closed shells.
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7.
  • Chen, S., et al. (författare)
  • Level structures of 56,58Ca cast doubt on a doubly magic 60Ca
  • 2023
  • Ingår i: Physics Letters B. - : Elsevier B.V.. - 0370-2693 .- 1873-2445. ; 843
  • Tidskriftsartikel (refereegranskat)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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8.
  • Chen, S., et al. (författare)
  • Quasifree Neutron Knockout from Ca-54 Corroborates Arising N=34 Neutron Magic Number
  • 2019
  • Ingår i: Physical Review Letters. - : AMER PHYSICAL SOC. - 0031-9007 .- 1079-7114. ; 123:14
  • Tidskriftsartikel (refereegranskat)abstract
    • Exclusive cross sections and momentum distributions have been measured for quasifree one-neutron knockout reactions from a Ca-54 beam striking on a liquid hydrogen target at similar to 200 MeV/u. A significantly larger cross section to the p(3/2), state compared to the f(5/2) state observed in the excitation of Ca-53 provides direct evidence for the nature of the N = 34 shell closure. This finding corroborates the arising of a new shell closure in neutron-rich calcium isotopes. The distorted-wave impulse approximation reaction formalism with shell model calculations using the effective GXPF1Bs interaction and ab initio calculations concur our experimental findings. Obtained transverse and parallel momentum distributions demonstrate the sensitivity of quasifree one-neutron knockout in inverse kinematics on a thick liquid hydrogen target with the reaction vertex reconstructed to final state spin-parity assignments.
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9.
  • Cortes, M. L., et al. (författare)
  • N=32 shell closure below calcium : Low-lying structure of Ar-50
  • 2020
  • Ingår i: Physical Review C. - : American Physical Society. - 2469-9985 .- 2469-9993. ; 102:6
  • Tidskriftsartikel (refereegranskat)abstract
    • Low-lying excited states in the N = 32 isotope Ar-50 were investigated by in-beam gamma-ray spectroscopy following proton- and neutron-knockout, multinucleon removal, and proton inelastic scattering at the RIKEN Radioactive Isotope Beam Factory. The energies of the two previously reported transitions have been confirmed, and five additional states are presented for the first time, including a candidate for a 3(-) state. The level scheme built using gamma gamma coincidences was compared to shell-model calculations in the sd-pf model space and to ab initio predictions based on chiral two- and three-nucleon interactions. Theoretical proton- and neutron-knockout cross sections suggest that two of the new transitions correspond to 2(+) states, while the previously proposed 4(1)(+) state could also correspond to a 2(+) state.
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10.
  • Cortes, M. L., et al. (författare)
  • Shell evolution of N=40 isotones towards Ca-60 : First spectroscopy of Ti-62
  • 2020
  • Ingår i: Physics Letters B. - : ELSEVIER. - 0370-2693 .- 1873-2445. ; 800
  • Tidskriftsartikel (refereegranskat)abstract
    • Excited states in the N = 40 isotone Ti-62 were populated via the V-63( p, 2p)Ti-62 reaction at similar to 200MeV/nucleonat the Radioactive Isotope Beam Factory and studied using gamma-ray spectroscopy. The energies of the 2(1)(+) -> 0(gs)(+) and 4(1)(+) -> 2(1)(+) transitions, observed here for the first time, indicate a deformed Ti-62 ground state. These energies are increased compared to the neighboring Cr-64 and Fe-66 isotones, suggesting a small decrease of quadrupole collectivity. The present measurement is well reproduced by large-scale shell-model calculations based on effective interactions, while ab initio and beyond mean-field calculations do not yet reproduce our findings. The shell-model calculations for Ti-62 show a dominant configuration with four neutrons excited across the N = 40 gap. Likewise, they indicate that the N = 40 island of inversion extends down to Z = 20, disfavoring a possible doubly magic character of the elusive Ca-60.
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11.
  • Das, Biswarup, et al. (författare)
  • Broken seniority symmetry in the semimagic proton mid-shell nucleus Rh 95
  • 2024
  • Ingår i: Physical Review Research. - : American Physical Society (APS). - 2643-1564. ; 6:2
  • Tidskriftsartikel (refereegranskat)abstract
    • Lifetime measurements of low-lying excited states in the semimagic (N=50) nucleus Rh95 have been performed by means of the fast-timing technique. The experiment was carried out using γ-ray detector arrays consisting of LaBr3(Ce) scintillators and germanium detectors integrated into the DESPEC experimental setup commissioned for the Facility for Antiproton and Ion Research (fair) Phase-0, Darmstadt, Germany. The excited states in Rh95 were populated primarily via the β decays of Pd95 nuclei, produced in the projectile fragmentation of a 850 MeV/nucleon Xe124 beam impinging on a 4g/cm2Be9 target. The deduced electromagnetic E2 transition strengths for the γ-ray cascade within the multiplet structure depopulating from the isomeric Iπ=21/2+ state are found to exhibit strong deviations from predictions of standard shell model calculations which feature approximately conserved seniority symmetry. In particular, the observation of a strongly suppressed E2 strength for the 13/2+→9/2+ ground state transition cannot be explained by calculations employing standard interactions. This remarkable result may require revision of the nucleon-nucleon interactions employed in state-of-the-art theoretical model calculations, and might also point to the need for including three-body forces in the Hamiltonian.
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12.
  • Das, B., et al. (författare)
  • Nature of seniority symmetry breaking in the semimagic nucleus Ru-94
  • 2022
  • Ingår i: Physical Review C. - : AMER PHYSICAL SOC. - 2469-9985 .- 2469-9993. ; 105:3
  • Tidskriftsartikel (refereegranskat)abstract
    • Direct lifetime measurements via gamma -gamma coincidences using a fast timing detector array consisting of LaBr3(Ce) scintillators has been applied to determine the lifetime of low-lying states in the semimagic (N = 50) nucleus Ru-94. The experiment was carried out as the first in a series of "FAIR-0" experiments with the DESPEC experimental setup at the Facility for Antiproton and Ion Research (FAIR). Excited states in Ru-94 were populated primarily via the beta-delayed proton emission of Pd-95 nuclei, produced in the projectile fragmentation of an 850 MeV/nucleon Xe-124 beam impinging on a 4 g/cm(2) Be-9 target. While the deduced E2 strength for the 2(+) -> 0(+) transition in the yrast cascade follows the expected behavior for conserved seniority symmetry, the intermediate 4(+) -> 2(+) transition exhibits a drastic enhancement of transition strength in comparison with pure-seniority model predictions as well as standard shell model predictions in the f pg proton hole space with respect to doubly magic Sn-100. The anomalous behavior is ascribed to a subtle interference between the wave function of the lowest seniority v = 2, I-pi = 4(+) state and that of a close-lying v = 4 state that exhibits partial dynamic symmetry. In addition, the observed strongly prohibitive 6(+) -> 4(+) transition can be attributed to the same mechanism but with a destructive interference. It is noted that such effects may provide stringent tests of the nucleon-nucleon interactions employed in state-of-the-art theoretical model calculations.
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13.
  • Elekes, Z., et al. (författare)
  • "Southwestern" boundary of the N=40 island of inversion : First study of low-lying bound excited states in 59V and 61V
  • 2022
  • Ingår i: Physical Review C. - : American Physical Society (APS). - 2469-9985 .- 2469-9993. ; 106:6
  • Tidskriftsartikel (refereegranskat)abstract
    • The low-lying level structure of 59V and 61V was investigated for the first time. The neutron knockout reaction and inelastic proton scattering were applied for 61V while the neutron knock-out reaction provided the data for 59V. Four and five new transitions were determined for 59V and 61V, respectively. Based on the comparison to our shell-model calculations using the Lenzi-Nowacki-Poves-Sieja (LNPS) interaction, three of the observed ?? rays for each isotope could be placed in the level scheme and assigned to the decay of the first 11/2??? and 9/2??? levels. The (p, p') excitation cross sections for 61V were analyzed by the coupled-channels formalism assuming quadrupole plus hexadecapole deformations. Due to the role of the hexadecapole deformation, 61V could not be unambiguously placed on the island of inversion.
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14.
  • Enciu, M., et al. (författare)
  • Extended p3/2 Neutron Orbital and the N=32 Shell Closure in 52Ca
  • 2022
  • Ingår i: Physical Review Letters. - : American Physical Society (APS). - 0031-9007 .- 1079-7114. ; 129:26
  • Tidskriftsartikel (refereegranskat)abstract
    • The one-neutron knockout from 52Ca in inverse kinematics onto a proton target was performed at similar to 230 MeV/nucleon combined with prompt 7 spectroscopy. Exclusive quasifree scattering cross sections to bound states in 51Ca and the momentum distributions corresponding to the removal of 1f7=2 and 2p3=2 neutrons were measured. The cross sections, interpreted within the distorted-wave impulse approximation reaction framework, are consistent with a shell closure at the neutron number N = 32, found as strong as at N = 28 and N = 34 in Ca isotopes from the same observables. The analysis of the momentum distributions leads to a difference of the root-mean-square radii of the neutron 1f7=2 and 2p3=2 orbitals of 0.61(23) fm, in agreement with the modified-shell-model prediction of 0.7 fm suggesting that the large root-mean-square radius of the 2p3=2 orbital in neutron-rich Ca isotopes is responsible for the unexpected linear increase of the charge radius with the neutron number.
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15.
  • Ertoprak, Aysegul, et al. (författare)
  • Evidence for octupole collectivity in 172Pt
  • 2020
  • Ingår i: European Physical Journal A. - : Springer. - 1434-6001 .- 1434-601X. ; 56:2
  • Tidskriftsartikel (refereegranskat)abstract
    • Excited states in the extremely neutron-deficient nucleus 172Pt were populated via 96Ru(78Kr,2p) and 92Mo(83Kr,3n) reactions. The level scheme has been extended up to an excitation energy of  ~ 5 MeV and tentative spin-parity assignments up to Iπ = 18+. Linear polarization and angular distribution measurements were used to determine the electromagnetic E1 character of the dipole transitions connecting the positive-parity ground-state band with an excited side-band, firmly establishing it as a negative-parity band. The lowest member of this negative-parity structure was firmly assigned spin-parity 3-. In addition, we observed an E3 transition from this 3- state to the ground state, providing direct evidence for octupole collectivity in 172Pt. Large-scale shell model (LSSM) and total Routhian surface (TRS) calculations have been performed, supporting the interpretation of the 3- state as a collective octupole-vibrational state.
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16.
  • Ghazi Moradi, Farnaz, 1976-, et al. (författare)
  • Character of particle-hole excitations in Ru-94 deduced from gamma-ray angular correlation and linear polarization measurements
  • 2014
  • Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 89:1, s. 014301-
  • Tidskriftsartikel (refereegranskat)abstract
    • Linear polarization and angular correlations of gamma-rays depopulating excited states in the neutron-deficient nucleus Ru-94(44)50 have been measured, enabling firm spin-parity assignments for several excited states in this nucleus. The deduced multipolarities of strong transitions in the yrast structure were found to be mostly of stretched M1, E1, and E2 types and, in most cases, in agreement with previous tentative assignments. The deduced multipolarity of the 1869 keV and the connecting 257 and 1641 keV transitions indicates that the state at 6358 keV excitation energy has spin parity 12(1)(-) rather than 12(3)(+) as proposed in previous works. The presence of a 12(1)(-) state is interpreted within the framework of large-scale shell-model calculations as a pure proton-hole state dominated by the pi(p(1/2)(-1)circle times g(9/2)(-5)) and pi(p(3/2)(-1) g(9/2)(-5)) configurations. A new positive-parity state is observed at 6103 keV and is tentatively assigned as 12(2)(+). The 14(1)(-) state proposed earlier is reassigned as 13(4)(-) and is interpreted as being dominated by neutron particle-hole core excitations. The strengths of several E1 transitions have been measured and are found to provide a signature of core-excited configurations.
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17.
  • Ghazi Moradi, Farnaz, et al. (författare)
  • Spectroscopy of the neutron-deficient N=50 nucleus Rh-95
  • 2014
  • Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 89:4, s. 044310-
  • Tidskriftsartikel (refereegranskat)abstract
    • The neutron-deficient semimagic (neutron number N = 50) Rh-95 nucleus has been produced at high spins using the projectile-target system Ca-40 + Ni-58 at 125 MeV beam energy. The gamma-decays of levels populated by the 3p fusion evaporation reaction channel were studied using gamma-gamma coincidences, and 20 new gamma-ray transitions involving 15 new positive-and negative-parity states were observed. Spin and parity for many of the excited states were firmly deduced for the first time using the combined directional angular correlation and direction-polarization techniques. The observed structures are discussed within the framework of large-scale shell model calculations. E1 transition strengths were deduced and used together with the results of the shell model calculations to study the contribution of different particle-hole configurations, in particular for analyzing contributions from core-excited configurations.
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18.
  • Juhasz, M. M., et al. (författare)
  • First spectroscopic study of( 51)Ar by the (p,2p) reaction
  • 2021
  • Ingår i: Physics Letters B. - : ELSEVIER. - 0370-2693 .- 1873-2445. ; 814
  • Tidskriftsartikel (refereegranskat)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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19.
  • Juhasz, M. M., et al. (författare)
  • First spectroscopic study of V-63 at the N=40 island of inversion
  • 2021
  • Ingår i: Physical Review C. - : AMER PHYSICAL SOC. - 2469-9985 .- 2469-9993. ; 103:6
  • Tidskriftsartikel (refereegranskat)abstract
    • The low-lying level structure of V-63 was studied for the first time by the inelastic proton scattering and the proton knock-out reaction in inverse kinematics. The comparison of the newly observed gamma-ray transitions at 696(8) keV and 889(16) keV with our shell-model calculations using the Lenzi-Nowacki-Poves-Sieja interaction established two excited states proposed to be the first 11/2(-) and 9/2(-) levels. The (p, p') excitation cross sections were analyzed by the coupled channel formalism assuming pure quadrupole as well as quadrupole+hexadecapole deformations. This resulted in large deformation parameters placing V-63 in the island of inversion located below Ni-68.
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20.
  • Koiwai, T., et al. (författare)
  • A first glimpse at the shell structure beyond Ca-54 : Spectroscopy of K-55, Ca-55, and Ca-57
  • 2022
  • Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 827, s. 136953-
  • Tidskriftsartikel (refereegranskat)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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21.
  • Koseoglou, P., et al. (författare)
  • Spectroscopy of neutron-rich scandium isotopes
  • 2020
  • Ingår i: Xxiii International School On Nuclear Physics, Neutron Physics And Applications. - : IOP Publishing. ; , s. 012026-
  • Konferensbidrag (refereegranskat)abstract
    • Within the SEASTAR III campaign at the Radioactive Isotope Beam Factory, at the RIKEN Nishina Center, neutron-rich isotopes in the vicinity of K-53 were produced from the fragmentation of the primary Zn-70 beam on a Be-9 target. After nucleon knockout reactions on the secondary liquid hydrogen MINOS target the known gamma rays of the neutron-rich Sc-55 isotope were observed (shown in this proceedings) and gamma rays from Sc-57,Sc-59 isotopes have been identified for the first time. The evolution of the occupied nucleon orbitals of these nuclei in the ground and excited state is investigated under the prism of the tensor force.
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22.
  • Li, P. J., et al. (författare)
  • Spectroscopy of deeply bound orbitals in neutron-rich Ca isotopes
  • 2024
  • Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 855
  • Tidskriftsartikel (refereegranskat)abstract
    • The calcium isotopes are an ideal system to investigate the evolution of shell structure and magic numbers. Although the properties of surface nucleons in calcium have been well studied, probing the structure of deeply bound nucleons remains a challenge. Here, we report on the first measurement of unbound states in Ca-53 and (55) Ca, populated from (54,56) Ca( p, pn) reactions at a beam energy of around 216 MeV/nucleon at the RIKEN Radioactive Isotopes Beam Factory. The resonance properties, partial cross sections, and momentum distributions of these unbound states were analyzed. Orbital angular momentum I assignments were extracted from momentum distributions based on calculations using the distorted wave impulse approximation (DWIA) reaction model. The resonances at excitation energies of 5516(41) keV in (53) Ca and 6000(250) keV in (55) Ca indicate a significant l = 3 component, providing the first experimental evidence for the v(0) f (7/2) single-particle strength of unbound hole states in the neutron-rich Ca isotopes. The observed excitation energies and cross-sections point towards extremely localized and well separated strength distributions, with some fragmentation for the v(0) f (7/2) orbital in (55) Ca. These results are in good agreement with predictions from shell-model calculations using the effective GXPF1Bs interaction and ab initio calculations and diverge markedly from the experimental distributions in the nickel isotones at Z = 28.
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23.
  • Linh, B. D., et al. (författare)
  • Onset of collectivity for argon isotopes close to N=32
  • 2024
  • Ingår i: Physical Review C. - : American Physical Society (APS). - 2469-9985 .- 2469-9993. ; 109:3
  • Tidskriftsartikel (refereegranskat)abstract
    • The shell closure at N = 32 has been investigated by a first spectroscopy of the N = 31 nucleus 49Ar at the Radioactive Isotope Beam Factory. Using the 50Ar(p, pn) reaction channel in inverse kinematics, 50Ar projectiles at 217 MeV/nucleon impinged on a 150 mm long liquid hydrogen target, part of the MINOS device. Prompt deexcitation gamma rays were measured with the NaI(Tl) array DALI2+. Reaction products were analyzed with the SAMURAI spectrometer, which allowed the measurement of the momentum distributions and angular momentum transfer. Data were compared to state-of-the-art theoretical predictions, including shell -model, energy -density functional, and ab initio calculations. An onset of collectivity is suggested besides the spherical configuration typical of a closed shell nucleus, such as for 52Ca.
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24.
  • Liu, Hongna, et al. (författare)
  • How Robust is the N=34 Subshell Closure? : First Spectroscopy of Ar-52
  • 2019
  • Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 122:7
  • Tidskriftsartikel (refereegranskat)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.
  •  
25.
  • Liu, Xiaoyu, et al. (författare)
  • Evidence for enhanced neutron-proton correlations from the level structure of theN = Z + 1 nucleus 87Tc
  • Ingår i: PHYSICAL REVIEW C.
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • The low-lying excited states in the neutron-deficient N = Z + 1 nucleus 8743 Tc 44 have been studiedvia the fusion-evaporation reaction 54 Fe( 36 Ar, 2n1p) 87 Tc at the Grand Accélérateur National d’IonsLourds (GANIL), France. The AGATA spectrometer was used in conjunction with the auxiliaryNEDA, Neutron Wall, and DIAMANT detector arrays to measure coincident prompt γ-rays, neutrons, and charged particles emitted in the reaction. A level scheme of 87 Tc from the (9/2 +g.s. ) state to the (33/2 +)statewasestablishedbasedon6mutuallycoincidentγ-ray transitions. The con-1structed level structure exhibits a rotational behavior with a sharp back bending at ~ω ≈ 0.50 MeV. A decrease in alignment frequency and increase in alignment sharpness in the odd-mass isotonic chains around N = 44 is proposed as an effect of the enhanced isoscalar neutron-proton interactions in odd-mass nuclei when approaching the N = Z line.
  •  
26.
  • Liu, X., et al. (författare)
  • Evidence for enhanced neutron-proton correlations from the levelstructure of the N= Z+ 1 nucleus 8743Tc44
  • 2021
  • Ingår i: Physical Review C. - : American Physical Society. - 2469-9985 .- 2469-9993. ; 104:2
  • Tidskriftsartikel (refereegranskat)abstract
    • The low-lying excited states in the neutron-deficient N = Z + 1 nucleus (87)(43)Tcc(44) have been studied via the fusion-evaporation reaction Fe-54(Ar-36, 2n1p)Tc-87 at the Grand Accelerateur National d'Ions Lourds (GANIL), France. The AGATA spectrometer was used in conjunction with the auxiliary NEDA, Neutron Wall, and DIAMANT detector arrays to measure coincident prompt gamma rays, neutrons, and charged particles emitted in the reaction. A level scheme of Tc-87 from the (9/2(g.s.)(+)) state to the (33/2(1)(+)) state was established based on six mutually coincident gamma-ray transitions. The constructed level structure exhibits a rotational behavior with a sharp backbending at (h) over bar omega approximate to 0.50 MeV. A decrease in alignment frequency and increase in alignment sharpness in the odd-mass isotonic chains around N = 44 is proposed as an effect of the enhanced isoscalar neutron-proton interactions in odd-mass nuclei when approaching the N = Z line.
  •  
27.
  • Liu, Xiaoyu, et al. (författare)
  • Evidence for Spherical-Oblate Shape Coexistence in 87Tc
  • Ingår i: THE EUROPEAN PHYSICAL JOURNAL A.
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • Excited states in the neutron-deficient nucleus 87 Tc have been studied via the fusion-evaporation reaction 54 Fe( 36 Ar, 2n1p) 87 Tc at 115 MeV beam energy. The AGATA γ-ray spectrometer coupled to the DIAMANT, NEDA, and Neutron Wall detector arrays for light-particle detection was used to measure the prompt coincidence of γ rays and light particles. Six transitions from the de-excitation of excited states belonging to a new band in 87 Tc were identified by comparing γ-ray intensities in the spectra gated under different reaction channel selection conditions. The constructed level structure was compared with the shell model and total Routhian surface calculations. The results indicate that the new band structure in 87 Tc is built on a spherical configuration, which is different from that assigned to the previously identified oblate yrast rotational band
  •  
28.
  • Liu, Xiaoyu, et al. (författare)
  • Evidence for spherical-oblate shape coexistence in Tc-87
  • 2022
  • Ingår i: Physical Review C. - : American Physical Society. - 2469-9985 .- 2469-9993. ; 106:3
  • Tidskriftsartikel (refereegranskat)abstract
    • Excited states in the neutron-deficient nucleus Tc-87 have been studied via the fusion-evaporation reaction 54Fe(36Ar, 2n1p) Tc-87 at 115 MeV beam energy. The AGATA gamma-ray spectrometer coupled to the DIAMANT, NEDA, and Neutron Wall detector arrays for light-particle detection was used to measure the prompt coincidence of gamma rays and light particles. Six transitions from the deexcitation of excited states belonging to a new band in Tc-87 were identified by comparing gamma-ray intensities in the spectra gated under different reaction channel selection conditions. The constructed level structure was compared with the shell model and total Routhian surface calculations. The results indicate that the new band structure in 87Tc is built on a spherical configuration, which is different from that assigned to the previously identified oblate yrast rotational band.
  •  
29.
  • Lv, B. F., et al. (författare)
  • Refined description of the positive-parity bands and the extent of octupole correlations in Ba-120
  • 2022
  • Ingår i: Physical Review C. - : American Physical Society (APS). - 2469-9985 .- 2469-9993. ; 105:4
  • Tidskriftsartikel (refereegranskat)abstract
    • Three new negative-parity bands have been identified in 120Ba, two of them forming a strongly coupled band. The previously known negative-parity band is significantly extended to high spin, while the lower part of the yrare positive-parity band has been modified. From the analysis of the band properties and comparison with the neighboring nuclei a coherent description of all bands is achieved. In particular, a simple explanation of the evolution of the positive-parity bands at high spin is proposed, including the possible occupation of the ??f7/2[541]1/2??? intruder orbital. Cranked Nilsson-Strutinsky calculations reveal similar quadrupole deformations but different triaxiality of the bands, while particle number conserving cranked shell model calculations qualitatively reproduce the experimental data and support the assigned configurations. The new measured ratios of reduced transition probabilities B(E1)/B(E2) complete the systematics in the 118???124Ba nuclei, exhibiting a decrease with decreasing neutron number, and are compared with the known values in the 116???120Xe nuclei, which are larger. Extended calculations with the quadrupole and octupole collective Hamiltonian based on the relativistic Hartree-Bogoliubov model employing the relativistic DD-PC1 density functional nicely reproduce the decreasing trend towards lower neutron numbers for Ba and Xe nuclei, as well as the larger values in Xe nuclei, but are much larger in amplitude than the experimental values. On the other hand, particle number conserving cranked shell model calculations without octupole deformation overestimate the low-spin values, while those with octupole deformation included reproduce the experimental values in 120Ba, suggesting the possible existence of moderate octupole collectivity in the negative-parity bands of nuclei in this mass region.
  •  
30.
  • Mistry, A. K., et al. (författare)
  • The DESPEC setup for GSI and FAIR
  • 2022
  • Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 1033, s. 166662-
  • Tidskriftsartikel (refereegranskat)abstract
    • The DEcay SPECtroscopy (DESPEC) setup for nuclear structure investigations was developed and commissioned at GSI, Germany in preparation for a full campaign of experiments at the FRS and Super-FRS. In this paper, we report on the first employment of the setup in the hybrid configuration with the AIDA implanter coupled to the FATIMA LaBr3(Ce) fast-timing array, and high-purity germanium detectors. Initial results are shown from the first experiments carried out with the setup. An overview of the setup and function is discussed, including technical advancements along the path. 
  •  
31.
  • Petrache, C. M., et al. (författare)
  • Collective rotation of an oblate nucleus at very high spin
  • 2019
  • Ingår i: Physical Review C. - : American Physical Society (APS). - 2469-9985 .- 2469-9993. ; 99:4
  • Tidskriftsartikel (refereegranskat)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. 
  •  
32.
  • Petrache, C. M., et al. (författare)
  • Evidence of chiral bands in even-even nuclei
  • 2018
  • Ingår i: Physical Review C. - : American Physical Society. - 2469-9985 .- 2469-9993. ; 97:4
  • Tidskriftsartikel (refereegranskat)abstract
    • Evidence for chiral doublet bands has been observed for the first time in the even-even nucleus Nd136. One chiral band was firmly established. Four other candidates for chiral bands were also identified, which can contribute to the realization of the multiple pairs of chiral doublet bands (MχD) phenomenon. The observed bands are investigated by the constrained and tilted axis cranking covariant density functional theory (TAC-CDFT). Possible configurations have been explored. The experimental energy spectra, angular momenta, and B(M1)/B(E2) values for the assigned configurations are globally reproduced by TAC-CDFT. Calculated results support the chiral interpretation of the observed bands, which correspond to shapes with maximum triaxiality induced by different multiquasiparticle configurations in Nd136.
  •  
33.
  • Petrache, C. M., et al. (författare)
  • High- K three-quasiparticle isomers in the proton-rich nucleus Nd 129
  • 2023
  • Ingår i: Physical Review C. - : American Physical Society (APS). - 2469-9985 .- 2469-9993. ; 108:1
  • Tidskriftsartikel (refereegranskat)abstract
    • Three three-quasiparticle isomers, one at an excitation energy of 2.3 MeV with T1/2=0.48(4)μs, and two shorter-lived with unknown half-lives at slightly lower energies have been identified in Nd129 using the MARA + JUROGAM 3 setup and the recoil tagging technique. All three isomers present decay patterns characteristic of high-K isomers. The known 6.7 s β-decaying isomer previously assigned to the 5/2+ level is now assigned to the new 7/2- ground state. A new low-spin 5/2+ isomeric state with a half-life of a few tens of nanoseconds has been identified, while a previously known 2.6 s β-decay activity was assigned to the band head of the ν1/2+[411] band. The transitions depopulating the high-K isomers to low-lying states also establish the relative energies of three low-lying one-quasiparticle bands, leading to a new spin-parity assignment of 7/2- to the ground state of Nd129. The partial half-lives of the depopulating transitions suggest spin-parities 21/2+, 19/2+, and 17/2+ for the three high-K isomers. The properties of the band built on the 21/2+ isomeric state suggest a one neutron-two proton configuration. Based on the results of extensive calculations with different models, we also assign one neutron-two proton configurations to the 19/2+ and 17/2+ isomeric states. The assigned configurations of the 17/2+ and 21/2+ isomeric states involve the π9/2+[404] orbital, which is identified in three-quasiparticle bands of proton-rich A≈130 nuclei.
  •  
34.
  • Petrache, C. M., et al. (författare)
  • Highly deformed bands in Nd nuclei : New results and consistent interpretation within the cranked Nilsson-Strutinsky formalism
  • 2019
  • Ingår i: Physical Review C. - : American Physical Society (APS). - 2469-9985 .- 2469-9993. ; 100:5
  • Tidskriftsartikel (refereegranskat)abstract
    • Three new highly-deformed (HD) bands are identified in Nd136 and the highly deformed band of Nd137 is extended at higher spin by four transitions, revealing a band crossing associated with the occupation of the second νi13/2 intruder orbital. Extended cranked Nilsson-Strutinsky calculations are performed for all HD bands observed in Nd134, Nd136, and Nd137, achieving for the first time a consistent interpretation of all HD bands in the Nd nuclei. The new interpretation has significant consequences, like the change of parity of the yrast HD bands of Nd134 and Nd136, and the involvement of two negative-parity neutron intruder orbitals in the configurations of most HD bands. The present experimental results and their theoretical interpretation represent an important step forward in the understanding of the second-minimum excitations in the Nd nuclei.
  •  
35.
  • Polettini, M., et al. (författare)
  • DESPEC Phase-0 campaign at GSI
  • 2021
  • Ingår i: NUOVO CIMENTO C-COLLOQUIA AND COMMUNICATIONS IN PHYSICS. - : SOC ITALIANA FISICA. - 2037-4909. ; 44:2-3
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper reports preliminary results of the DESPEC campaign at GSI, focused on the study of neutron-deficient nuclei approaching Sn-100. The results presented show the isomeric decays of excited states with I-pi = 14(+) and 8(+) in Pd-96 and Pd-94, respectively. The detailed characterisation of the DESPEC set-up and analysis methodologies, proven in this experimental run, are crucial for the future campaigns.
  •  
36.
  • Recchia, F., et al. (författare)
  • Isomer spectroscopy in odd–even Ti isotopes : Approaching n = 40
  • 2019
  • Ingår i: Acta Physica Polonica B. - : Jagellonian University. - 0587-4254 .- 1509-5770. ; 50:3, s. 669-674
  • Tidskriftsartikel (refereegranskat)abstract
    • Our understanding of the evolution of the shell structure in nuclei far from stability is based on the study of some key nuclei. Nuclei at or next to double shell closures play a special role in this. Presently, a lot of discussion is concentrated on the neutron-rich calcium isotopes, which provide a rich testing ground for various nuclear models with several traditional and new magic numbers. 60 Ca is now almost within reach with the most advanced radioactive beam facilities. In order to investigate the evolution of the shell gap at N = 40, the configuration of states in the odd–even titanium isotopes up to N = 37 ( 59 Ti) have been studied. In order to experimentally access the shell gap at N = 40, it is nowadays within the reach of the most advanced facility the investigation of neutron hole configuration states in odd–even titanium isotopes up to N = 37, in the 59 Ti nucleus. Such states correspond to relatively simple configurations that constitute a challenging testing ground for effective nuclear interactions. The new data obtained in our experiment allows to place the present predictions concerning the shell closure at N = 40 in the calcium region on a more solid ground. 
  •  
37.
  • Sun, Y. L., et al. (författare)
  • Restoration of the natural E(1/2(1)(+)) - E(3/2(1)(+)) energy splitting in odd -K isotopes towards N=40
  • 2020
  • Ingår i: Physics Letters B. - : ELSEVIER. - 0370-2693 .- 1873-2445. ; 802
  • Tidskriftsartikel (refereegranskat)abstract
    • We report on the first gamma-ray spectroscopy of K-51,K-53 produced via the Ca-52,Ca-54(p,2p) reactions at similar to 250 MeV/nucleon. Unambiguous final-state angular-momentum assignments were achieved for beam intensities down to few particles per second by using a new technique based on reaction vertex tracking combined with a thick liquid-hydrogen target. Through gamma-ray spectroscopy and exclusive parallel momentum distribution analysis, 3/(2)+ ground states and 1/2(+) first excited states in K-51,K-53 were established quantifying the natural ordering of the 1d(3/2) and 2s(1/2) proton-hole states that are restored at N = 32 and 34. State-of-the-art ab initio calculations and shell-model calculations with improved phenomenological effective interactions reproduce the present data and predict consistently the increase of the E(1/4)- E(3/4) energy differences towards N = 40.
  •  
38.
  • Wimmer, K., et al. (författare)
  • First spectroscopy of Ti-61 and the transition to the Island of Inversion at N=40
  • 2019
  • Ingår i: Physics Letters B. - : Elsevier. - 0370-2693 .- 1873-2445. ; 792, s. 16-20
  • Tidskriftsartikel (refereegranskat)abstract
    • Isomeric states in Ti-59,Ti-61 have been populated in the projectile fragmentation of a 345 AMeV( 238)U beam at the Radioactive Isotope Beam Factory. The decay lifetimes and delayed gamma-ray transitions were measured with the EURICA array. Besides the known isomeric state in Ti-59, two isomeric states in Ti-61 are observed for the first time. Based on the measured lifetimes, transition multipolarities as well as tentative spins and parities are assigned. Large-scale shell model calculations based on the modified LNPS interaction show that both Ti-59 and Ti-61 belong to the Island of Inversion at N = 40 with ground state configurations dominated by particle-hole excitations to the g(9/2 )and d(5/2) orbits.
  •  
39.
  • Wimmer, K., et al. (författare)
  • Isomeric states in neutron-rich nuclei near N=40
  • 2021
  • Ingår i: Physical Review C. - : American Physical Society (APS). - 2469-9985 .- 2469-9993. ; 104:1
  • Tidskriftsartikel (refereegranskat)abstract
    • Neutron-rich nuclei in the vicinity of the N = 40 island of inversion are characterized by shell evolution and exhibit deformed ground states. In several nuclei isomeric states have been observed and attributed to excitations to the intruder neutron 1g(9/2) orbital. In the present paper we searched for isomeric states in nuclei around N = 40, Z = 22 produced by projectile fragmentation at the Radioactive Isotope Beam Factory. Delayed. rays were detected by the Euroball RIKEN Cluster Array germanium detector array gamma High statistics data allowed for an updated decay scheme of V-60. The lifetime of an isomeric state in V-64 was measured for the first time in the present experiment. A previously unobserved isomeric state was discovered in Sc-58. The measured lifetime suggests a parity changing transition, originating from an odd number of neutrons in the 1g(9/2) orbital. The nature of the isomeric state in Sc-58 is, thus, different from isomers in the less exotic V and Sc nuclei.
  •  
40.
  • Yaneva, A., et al. (författare)
  • FAST-TIMING MEASUREMENT IN 96Pd: IMPROVED ACCURACY FOR THE LIFETIME OF THE 4+1 STATE
  • 2023
  • Ingår i: Acta Physica Polonica B, Proceedings Supplement. - : Jagiellonian University. - 1899-2358 .- 2082-7865. ; , s. 1-1
  • Konferensbidrag (refereegranskat)abstract
    • Direct lifetime measurements via γ–γ coincidences using the FATIMA fast-timing LaBr3(Ce) array were performed for the excited states below previously reported isomers. In the N = 50 semi-magic 96Pd nucleus, lifetimes below the Iπ = 8+ seniority isomer were addressed as a benchmark for further analysis. The results for the Iπ = 2+ and 4+ states confirm the published values. Increased accuracy for the lifetime value was achieved for the 4+ state.
  •  
41.
  • Yaneva, A., et al. (författare)
  • The shape of the Tz = +1 nucleus 94Pd and the role of proton-neutron interactions on the structure of its excited states
  • 2024
  • Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 855
  • Tidskriftsartikel (refereegranskat)abstract
    • Reduced transition probabilities have been extracted between excited, yrast states in the N=Z+2 nucleus 94Pd. The transitions of interest were observed following decays of the Iπ=14+, Ex=2129-keV isomeric state, which was populated following the projectile fragmentation of a 124Xe primary beam at the GSI Helmholtzzentrum für Schwerionenforschung accelerator facility as part of FAIR Phase-0. Experimental information regarding the reduced E2 transition strengths for the decays of the yrast 8+ and 6+ states was determined following isomer-delayed Eγ1−Eγ2−△T2,1 coincidence method, using the LaBr3(Ce)-based FATIMA fast-timing coincidence gamma-ray array, which allowed direct determination of lifetimes of states in 94Pd using the Generalized Centroid Difference (GCD) method. The experimental value for the half-life of the yrast 8+ state of 755(106) ps results in a reduced transition probability of B(E2:8→+6+) = 205−25+34 e2 fm4, which enables a precise verification of shell-model calculations for this unique system, lying directly between the N=Z line and the N=50 neutron shell closure. The determined B(E2) value provides an insight into the purity of (g9/2)n configurations in competition with admixtures from excitations between the (lower) N=3pf and (higher) N=4gds orbitals for the first time. The results indicate weak collectivity expected for near-zero quadrupole deformation and an increasing importance of the T=0 proton-neutron interaction at N=48.
  •  
42.
  • Zhang, W., et al. (författare)
  • Decay spectroscopy of 171,172Os and 171,172,174Ir
  • 2023
  • Ingår i: Physical Review C. - : American Physical Society (APS). - 2469-9985 .- 2469-9993. ; 107:1
  • Tidskriftsartikel (refereegranskat)abstract
    • We report on a study of the α-decay fine structure and the associated Eα−Eγ correlations in the decays of 171,172Os and 171,172,174Ir. In total, 13 new α-decay energy lines have been resolved, and three new γ-ray transitions have been observed following the new decay branches to 168Re and 167W. The weak α-decay branch from the bandhead of the νi13/2 band in 171Os observed in this work highlights an unusual competition between α, β, and electromagnetic decays from this isomeric state. The nucleus 171Os is therefore one of few nuclei observed to exhibit three different decay modes from the same excited state. The nuclei of interest were produced in 92Mo(83Kr,xpyn) fusion-evaporation reactions at the Accelerator Laboratory of the University of Jyväskylä, Finland. The fusion products were selected using the gas-filled ion separator RITU and their decays were characterized using an array of detectors for charged particles and electromagnetic radiation known as GREAT. Prompt γ-ray transitions were detected and correlated with the decays using the JUROGAM II germanium detector array surrounding the target position. Results obtained from total Routhian surface (TRS) calculations suggest that α-decay fine structure and the associated hindrance factors may be a sensitive probe of even relatively small shape changes between the final states in the daughter nucleus.
  •  
43.
  • Zhang, Wei, et al. (författare)
  • Identification of excited states in Te55 52107
  • 2021
  • Ingår i: Physical Review C. Nuclear Physics. - : American Physical Society. - 0556-2813 .- 1089-490X. ; 104:6
  • Tidskriftsartikel (refereegranskat)abstract
    • Excited states in the extremely neutron-deficient nucleus Te107 have been identified from two separate experiments using the recoil-decay tagging technique. Two connected structures were observed on the basis of γγ-coincidence relations and tentatively assigned as built on the mixed-parentage νg7/2d5/2 and νh11/2 intruder configurations. The observed structures were compared with large-scale shell-model calculations and total Routhian surface calculations. Collective behavior was discovered to persist in the νh11/2 band of Te107 which highlights the shape-polarizing effect of a single valence neutron occupying the h11/2 intruder orbit as the N=50 shell closure is approached.
  •  
44.
  • Zhang, Wei, et al. (författare)
  • 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
  • Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 820
  • Tidskriftsartikel (refereegranskat)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.
  •  
45.
  • Zhang, Wei, et al. (författare)
  • Observation of the proton emitter 11657La59
  • 2022
  • Ingår i: Communications Physics. - : Springer Science and Business Media LLC. - 2399-3650. ; 5:1
  • Tidskriftsartikel (refereegranskat)abstract
    • The quantum tunneling and emission of a single constituent nucleon provide a beautifully simple and unique window into the complex properties of atomic nuclei at the extreme edge of nuclear existence. In particular, for odd-odd proton emitting nuclides, the associated decay energy and partial half-life can be used to probe the correlations between the valence neutrons and protons which have been theoretically predicted to favour a new type of nuclear superfluidity, isoscalar neutron-proton pairing, for which the experimental “smoking gun" remains elusive. In the present work, proton emission from the lanthanum isotope 1165757116La59, 23 neutrons away from the only stable isotope 1395757139La82, is reported. 116La nuclei were synthesised in the fusion-evaporation reaction 58Ni(64Zn, p5n)116La and identified via their proton radioactivity using the mass spectrometer MARA (Mass Analysing Recoil Apparatus) and the silicon detectors placed at its focal plane. Comparisons of the measured proton energy (Ep = 718 ± 9 keV) and half-life (T1/2 = 50 ± 22 ms) with values calculated using the Universal Decay Law approach indicate that the proton is emitted with an orbital angular momentum l = 2 and that its emission probability is enhanced relative to its closest, less exotic, odd-even lanthanum isotope (1175757117La60) while the proton-emission Q-value is lower. We propose this to be a possible signature for the presence of strong neutron-proton pair correlations in this exotic, neutron deficient system. The observations of γ decays from isomeric states in 116La and 117La are also reported.
  •  
46.
  • Zhang, Wei, et al. (författare)
  • Observation of the proton emitter La-116(57)59
  • 2022
  • Ingår i: Communications Physics. - : Springer Nature. - 2399-3650. ; 5:1
  • Tidskriftsartikel (refereegranskat)abstract
    • The quantum tunneling and emission of a single constituent nucleon provide a beautifully simple and unique window into the complex properties of atomic nuclei at the extreme edge of nuclear existence. In particular, for odd-odd proton emitting nuclides, the associated decay energy and partial half-life can be used to probe the correlations between the valence neutrons and protons which have been theoretically predicted to favour a new type of nuclear superfluidity, isoscalar neutron-proton pairing, for which the experimental "smoking gun" remains elusive. In the present work, proton emission from the lanthanum isotope La-116(57)59, 23 neutrons away from the only stable isotope La-139(57)82, is reported. La-116 nuclei were synthesised in the fusion-evaporation reaction Ni-58(Zn-64, p5n)La-116 and identified via their proton radioactivity using the mass spectrometer MARA (Mass Analysing Recoil Apparatus) and the silicon detectors placed at its focal plane. Comparisons of the measured proton energy (E-p = 718 +/- 9 keV) and half-life (T-1/2 = 50 +/- 22 ms) with values calculated using the Universal Decay Law approach indicate that the proton is emitted with an orbital angular momentum l = 2 and that its emission probability is enhanced relative to its closest, less exotic, odd-even lanthanum isotope (La-117(57)60) while the proton-emission Q-value is lower. We propose this to be a possible signature for the presence of strong neutron-proton pair correlations in this exotic, neutron deficient system. The observations of. decays from isomeric states in La-116 and La-117 are also reported.
  •  
47.
  • Zheng, K. K., et al. (författare)
  • Candidate revolving chiral doublet bands in Cs-119
  • 2022
  • Ingår i: European Physical Journal A. - : Springer Nature. - 1434-6001 .- 1434-601X. ; 58:3
  • Tidskriftsartikel (refereegranskat)abstract
    • Two rotational hands are identified in Cs-119, one of which having very similar pattern to that of the strongly-coupled pi g(9/2)[404]9/2(+) band. The properties of the bands with similar patterns extracted from the experimental data are in agreement with a chiral interpretation. Tilted axis cranking covariant density functional theory with pairing correlations and particle-number conserving cranked shell model calculations are employed to determine the deformation and to investigate the band configurations, respectively. It results that the backbending is induced by the rotational alignment of two h(11/2 )protons, whose angular momenta reorient from the short to the intermediate axis, in a plane orthogonal to the angular momentum of the strongly-coupled g(9/2) proton which keeps aligned along the long axis. The total spin points in 3D, inducing the breaking of the chiral symmetry. This is the first observation of candidate chiral bands built on a configuration with three protons, one in the strongly coupled [404]9/2(+) orbital which does not change orientation with increasing rotational frequency, and two in the h(1)(1/)(2) orbital which reorients to the rotation axis. The bands are observed in the transient backbending regime, showing that the chirality in nuclei is a general phenomenon, being robust and present not only in nuclei with nearly maximal triaxiality and pure configurations, but also in nuclei with moderate triaxiality and mixed configurations which gradually evolve from one to three-quasiparticle configurations, like in the backbending region.
  •  
48.
  • Zheng, K. K., et al. (författare)
  • Complete set of proton excitations in Cs-119
  • 2021
  • Ingår i: Physical Review C. - : American Physical Society (APS). - 2469-9985 .- 2469-9993. ; 104:4
  • Tidskriftsartikel (refereegranskat)abstract
    • The very neutron-deficient strongly deformed Cs-119 nucleus has been studied using the Ni-58(Zn-64, 3p) reaction and the JUROGAM 3 gamma-ray detector array coupled to the MARA recoil-mass separator setup. The excitation energies of all observed bands have been determined, spins and parities have been firmly assigned to most of the observed states. The previously known and the newly identified rotational bands have been extended to very high spin and excitation energy. The configurations of the observed bands are discussed using the particle number conserving cranked shell model. The present study establishes the largest set of rotational bands observed in the proton-rich A approximate to 120 mass region.
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49.
  • Zheng, K. K., et al. (författare)
  • Evidence of oblate-prolate shape coexistence in the strongly-deformed nucleus Cs-119
  • 2021
  • Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 822
  • Tidskriftsartikel (refereegranskat)abstract
    • Prolate-oblate shape coexistence close to the ground state in the strongly-deformed proton-rich A approximate to 120nuclei is reported for the first time. One of the four reported bands in Cs-119, built on a 11/2- state at 670 keV, consists of nearly degenerate signature partners, and has properties which unequivocally indicate the strongly-coupled pi h(11/2)[505]11/2(-) configuration associated with oblate shape. Together with the decoupled pi h(11/2[)541]3/2(-) band built on the 11/2- prolate state at 110 keV, for which a half-life of T-1/2 = 55(5) mu shas been measured, the new bands bring evidence of shape coexistence at low spin in the proton-rich strongly deformed A approximate to 120 nuclei, a phenomenon predicted since long time, but not yet observed. Calculations using the particle-number conserving cranked shell model and two dimensional tilted axis cranking covariant density functional theory support and well reproduce the observed oblate and prolate coexisting low-energy states in Cs-119.
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50.
  • Zheng, K. K., et al. (författare)
  • Neutron excitations in Ba-119
  • 2021
  • Ingår i: Physical Review C. - : American Physical Society (APS). - 2469-9985 .- 2469-9993. ; 104:1
  • Tidskriftsartikel (refereegranskat)abstract
    • The neutron-deficient Ba-119 nucleus has been studied using the Ni-58(Zn-64, 2pn) reaction and the JUROGAM 3 y -ray detector array coupled to the MARA recoil-mass separator setup. One new rotational band and several low-lying states are newly identified. A half-life of T112 = 0.36(2) mu s has been measured for the 5/2(-) bandhead of the nu h(11/2) band. The two previously known rotational bands are confirmed, except for the higher part of the +1/2 signature partner of the positive-parity band. Configurations are assigned based on the analysis of the observed quasiparticle alignments whose nature is unveiled by the calculations using the particle number conserving cranked shell model.
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