Beta Decay of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow /><mml:mrow><mml:mn>68</mml:mn><mml:mo>–</mml:mo><mml:mn>74</mml:mn></mml:mrow></mml:msup></mml:mrow><mml:mi>Ni</mml:mi></mml:math>and Level Structure of Neutron-Rich Cu Isotopes

Franchoo, S.; Huyse, M.; Kruglov, K.; Kudryavtsev, Yu. A.; Mueller, W. F.; Raabe, R.; Reusen, I.; Duppen, P. Van; Roosbroeck, J. Van; Vermeeren, L.; Wöhr, A.; Kratz, K. L.; Pfeiffer, B.; Walters, W. B.

doi:10.1103/physrevlett.81.3100

Cited by 141 publications

(119 citation statements)

References 25 publications

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“…Blocking cross-shell excitations above Z ¼ 28 inaccurately described the 1=2 − state systematics and the 71;73 Cu magnetic moments [10,11], whereas allowing proton excitations from the f 7=2 level gave a good description of the evolution of the 1=2 − state with N [12]. Similar conclusions resulted from the Coulomb-excitation study of the neighboring zinc isotopes: with an inert…”

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confidence: 64%

Doubly Magic Nickel

Bazin

2017

Physics

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The masses of the neutron-rich copper isotopes [75][76][77][78][79] Cu are determined using the precision mass spectrometer ISOLTRAP at the CERN-ISOLDE facility. The trend from the new data differs significantly from that of previous results, offering a first accurate view of the mass surface adjacent to the Z ¼ 28, N ¼ 50 nuclide 78 Ni and supporting a doubly magic character. The new masses compare very well with large-scale shell-model calculations that predict shape coexistence in a doubly magic 78Ni and a new island of inversion for Z < 28. A coherent picture of this important exotic region begins to emerge where excitations across Z ¼ 28 and N ¼ 50 form a delicate equilibrium with a spherical mean field. DOI: 10.1103/PhysRevLett.119.192502 The Z ¼ 28, N ¼ 50 region of the nuclear chart is a focus of today's experimental and theoretical nuclearstructure research with the nuclide 78Ni representing a frontier. Over the years experiments with radioactive-ion beams have shown that the stability of nuclear magic numbers breaks down in light, exotic nuclei as reviewed in Ref. [1]. The stakes for 78Ni are double, as it lies at the intersection of the classical proton and neutron shell closures Z ¼ 28 and N ¼ 50, respectively. Whether the exotic 78 Ni retains the exceptional stability of the classic closed-shell nuclides is an open question, upon which depends the correct description of medium-mass, neutronrich nuclei.Crucial for developing more reliable solutions to the nuclear many-body problem is the understanding of the mechanism driving shell evolution in exotic nuclei. In the shell model, the tensor force has been proposed as a fundamental ingredient [2]. With the advances in effective field theory and in-medium similarity renormalization group methods [3], shell-closure signatures become important links between shell-model and ab initio approaches, as recently illustrated for the purported magic numbers N ¼ 32 [4][5][6] and N ¼ 34 [7]. This complementarity was recently highlighted with the structure of 78 Ni described using two such approaches: a large-scale shell-model calculation [8] and a coupled-cluster calculation using a chiral Hamiltonian [9]. The two calculations agree on the excitation energy of the first 2 þ state, suggesting doubly magic character. However, the shell-model calculations also predict an intruder 0 þ 2 state at a lower excitation energy than the 2 þ state, hinting at a new (fifth) island of inversion following those at N ¼ 8, 20, 28, and 40 [8]. While these predictions cannot yet be tested directly with the concerned N ¼ 50 isotones, the copper isotopes in the vicinity of 78Ni provide an excellent proxy, as the ensemble of ground-state properties and spectroscopy is very sensitive to the two-body matrix elements promoting protons across Z ¼ 28 and neutrons across N ¼ 50. Blocking cross-shell excitations above Z ¼ 28 inaccurately described the 1=2 − state systematics and the 71;73 Cu magnetic moments [10,11], whereas allowing proton excitations from the f 7=2 level gave a good descr...

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confidence: 64%

Doubly Magic Nickel

Bazin

2017

Physics

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“…spin I ¼ 3=2 for all odd-A Ga isotopes. However, in the Cu isotones with two protons fewer, it has been demonstrated that the proton SP ordering changes when neutrons start occupying the g 9=2 orbital around N ¼ 40 [5][6][7][8][9][10][11][12][13][14][15]. An inversion of the p 3=2 and f 5=2 SP levels was established recently in 75 Cu at N ¼ 46 [11], where the 5=2 À g.s.…”

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Nuclear Spins and Moments of Ga Isotopes Reveal Sudden Structural Changes betweenN=40andN=50

et al. 2010

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Collinear laser spectroscopy was performed on Ga (Z ¼ 31) isotopes at ISOLDE, CERN. A gas-filled linear Paul trap (ISCOOL) was used to extend measurements towards very neutron-rich isotopes (N ¼ 36-50 Nuclear structure has for some time been described by the single-particle (SP) states of nucleons in the shell model. The evolution and reordering of these levels along isotopic chains is explored at radioactive ion beam facilities to provide information on the nature of the nucleonnucleon interaction. Key to these studies is the determination of the value of the nuclear spin of each state, which provides a means of level identification. Whereas the spin may sometimes be inferred from nuclear decay and -spectroscopy data, laser spectroscopy [1,2] permits a measurement of the nuclear spin, in addition to the state's magnetic dipole and electric quadrupole moments. The latter two observables are very sensitive to the wave function and thus to the SP shell evolution. The sensitivity of the laser technique has been critically enhanced using bunched beams from a gas-filled linear rf quadrupole known as an ion beam cooler [3]. In this Letter we report the application of ISCOOL [4]-an ion beam cooler recently installed at ISOLDE-for collinear laser spectroscopy on Ga isotopes from stable to the magic N ¼ 50 shell gap, located 15 isotopes away from stability. For the first time g.s. spins have been measured, revealing sudden changes not observed in earlier experiments.The Ga isotopes have three protons outside the Z ¼ 28 shell gap. In a normal shell-model ordering, the three protons would occupy the p 3=2 level, leading to a g.s. spin I ¼ 3=2 for all odd-A Ga isotopes. However, in the Cu isotones with two protons fewer, it has been demonstrated that the proton SP ordering changes when neutrons start occupying the g 9=2 orbital around N ¼ 40 [5][6][7][8][9][10][11][12][13][14][15]. An inversion of the p 3=2 and f 5=2 SP levels was established recently in 75 Cu at N ¼ 46 [11], where the 5=2 À g.s. is near degenerate with a 3=2 À and 1=2 À state [11]. In this Letter we establish the g.s. spins and structure of the odd-A Ga isotopes from N ¼ 36 up to the N ¼ 50 shell closure, and we investigate the systematics of the 1=2 À , 3=2 À and 5=2 À levels.Fission fragments were produced in a thick UC x target (45 g=cm 2 ) using 1.4 GeV protons at an average current of $2 A. A proton-neutron converter [16] was used to suppress the Rb production. The Ga yield was selectively enhanced by a factor of 100 using the Resonant Ionization Laser-Ion Source [17], extracted and accelerated to 30 keV and mass selected. The ions were cooled and bunched by the newly-installed ISCOOL [4] and delivered to the collinear laser spectroscopy setup [18]. The ion beam was

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“…This region presents a key proving ground for the latest shell-model interactions, since it offers an attractively simple structure of the excited states in terms of particle-particle or particle-hole couplings. A compelling question in this region is related to the rapid reduction in energy of the 5/2 − state as the νg 9/2 orbital is filled in the Cu isotopes [1,2]. Given that this state remains static at approximately 1 MeV as neutrons fill the fp shell, its abrupt change at N = 40 garnered a great deal of interest and motivated further experimental and theoretical attention [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17].…”

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Experimental determination of anIπ=2−ground state inCu72

et al. 2010

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This article reports on the ground-state spin and moments measured in 72,74 Cu using collinear laser spectroscopy at the CERN On-Line Isotope Mass Separator (ISOLDE) facility. From the measured hyperfine coefficients, the nuclear observables µ( 72 Cu) = −1.3472(10)µ N , µ( 74 Cu) = −1.068(3)µ N , Q( 72 Cu) = +8(2) efm 2 , Q( 74 Cu) = +26(3) efm 2 , I ( 72 Cu) = 2, and I ( 74 Cu) = 2 have been determined. Through a comparison of the measured magnetic moments with different models, the negative moment reveals a strong πf 5/2 ⊗ νg 9/2 component in the ground-state wave function. Consequently, a negative parity has been assigned to the ground states of 72,74 Cu. Large-scale shell-model calculations illustrate the strong sensitivity of the nuclear moments to configuration mixing and to the effective interaction employed. The neutron-rich nuclei surrounding the Z = 28 and N = 50 shell closures have received a great deal of experimental and theoretical attention in the last decade. This region presents a key proving ground for the latest shell-model interactions, since it offers an attractively simple structure of the excited states in terms of particle-particle or particle-hole couplings. A compelling question in this region is related to the rapid reduction in energy of the 5/2 − state as the νg 9/2 orbital is filled in the Cu isotopes [1,2]. Given that this state remains static at approximately 1 MeV as neutrons fill the fp shell, its abrupt change at N = 40 garnered a great deal of interest and motivated further experimental and theoretical attention [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. A major step in understanding the evolution of nuclear structure in this region was the suggestion to include the monopole term from the tensor force interaction [18,19]. This work predicted a reduction in energy of the 5/2 − state and an inversion with the 3/2 − state in the mid-shell region, which was recently confirmed to occur at N = 46 in the odd-Cu isotopes [20]. Effective shell-model interactions which include this effect have recently been developed in the fpg model space. Two of these interactions start from a 56 Ni core [21,22], while the most recent one also includes excitations of protons from the πf 7/2 orbit across Z = 28 [23]. The odd-odd Cu isotopes are an ideal testing ground for these models, as their properties are extremely sensitive to the proton-neutron interaction.Recent beta-decay studies of 72 Ni [8] have tentatively assigned a spin I = 2 to the ground state (gs) of 72 Cu. Shell-model calculations, based on effective and realistic interactions, could not reproduce such gs spin [8], but placed the 2 − and 2 + states around 400 keV. A gs spin I = 2 is particularly interesting since the spins of 71,73 Cu now have been measured as I = 3/2, and their magnetic moments are compatible with a leading πp 3/2 configuration [20]. However, a [πp 3/2 ⊗ νg 3 9/2 , σ = 1] cannot couple to spin 2, so this configuration cannot be the leading term in the gs wave function of 72 Cu. Alternatively it could be...

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Beta Decay of68–74Niand Level Structure of Neutron-Rich Cu Isotopes

Cited by 141 publications

References 25 publications

Doubly Magic Nickel

Doubly Magic Nickel

Nuclear Spins and Moments of Ga Isotopes Reveal Sudden Structural Changes betweenN=40andN=50

Experimental determination of anIπ=2−ground state inCu72

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