Enhanced collectivity in 74Ni

Abstract

The neutron-rich nucleus 74Ni was studied with inverse-kinematics inelastic proton scattering using a 74Ni radioactive beam incident on a liquid hydrogen targetat a center-of-mass energy of 80 MeV. From the measured de-excitation gamma-rays, the population of the first 2+ state was quantified. The angle-integrated excitation cross section was determined to be 14(4) mb. A deformation length of delta = 1.04(16) fm was extracted in comparison with distorted wave theory, which suggests that the enhancement of collectivity established for 70Ni continues up to 74Ni. A comparison with results of shell model and quasi-particle random phase approximation calculations indicates that the magic character of Z = 28 or N = 50 is weakened in 74Ni

Direct Lifetime Measurements of the Excited States inNi72

“…In red we show the result for 72 Ni obtained from this experiment. This result is much lower than the previously indicated trend measured with Coulomb excitation for 70 Ni [1] and the (p, p ′ ) experiment for 74 Ni [3]. It is, however, closer (within the error bars) to the new result from Coulomb excitation measurement of 74 Ni [4], confirming the indication of normal rather than enhanced (as reported in [1]) corepolarization picture in neutron-rich nickel isotopes.…”

“…This experimental result was later interpreted with a theoretical shell model calculation [2]. The enhanced collectivity in nickel isotopes for N > 40 was also reported in 74 Ni (N = 46) [3] where a large transition strength was deduced from the deformation parameter measured in the 2 + inelastic scattering cross-section measurement. This value, however, was not confirmed in a recent Coulomb excitation measurement at 95.8A MeV where the reduced probability was found to be lower, posing a question about the degree of enhanced collectivity in this region [4].…”

Ab initiomultireference in-medium similarity renormalization group calculations of even calcium and nickel isotopes

“…Such a study is timely, because neutron-rich calcium isotopes have been the focus of ongoing experimental campaigns [23][24][25][26][27][28], and investigations of proton-rich Ca isotopes are planned for the near future. Likewise, there is continued interest in neutron-rich Ni isotopes [29][30][31][32][33][34][35][36].…”

Evolution of collectivity in the78Ni region: Coulomb excitation of74Ni at intermediate energies.

“…The analysis is under completion and a fine tuning of the experimental setup simulation is needed in order to finalize the result. Despite this, preliminary estimations do not show evidences of collectivity enhancement, displaying a B(E2) value about 40% lower than the one obtained in the (p,p') experiment by Aoi and collaborators in [1]. Figure 3 shows some theoretical expectations and the experimental evaluation performed in [11] for the neutron rich side of the Ni isotopic chain.…”

“…a proton scattering experiment (see [1]). Since this last technique is sensible to both the nuclear and Coulomb interactions, the 40% difference in the B(E2) that our data seems to indicate could be a hint of the neutron and proton shells de-coupling in presence of a strong neutron excess, leading to different proton/neutron core deformations.…”