Is seniority a partial dynamic symmetry in the first νg9/2 shell?
2018
The low-lying structures of the midshell νg9/2 Ni isotopes 72Ni and 74Ni have been investigated at the RIBF facility in RIKEN within the EURICA collaboration. Previously unobserved low-lying states were accessed for the first time following β decay of the mother nuclei 72Co and 74Co. As a result, we provide a complete picture in terms of the
seniorityscheme up to the first (8+) levels for both nuclei. The experimental results are compared to
shell-modelcalculations in order to define to what extent the
seniorityquantum number is preserved in the first neutron g9/2 shell. We find that the disappearance of the
seniorityisomerism in the View the
MathMLsource states can be explained by a lowering of the
seniority-four (6+) levels as predicted years ago. For 74Ni, the internal de-excitation pattern of the newly observed View the
MathMLsource state supports a restoration of the normal
seniorityordering up to spin J=4. This property, unexplained by the
shell-modelcalculations, is in agreement with a dominance of the single-particle spherical regime near 78Ni.
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