Abstract
The gamma-ray decay of excited states of the one-valence-proton nucleus 133Sb has been studied using cold-neutron induced fission of 235U and 241Pu targets, during the EXILL campaign at the ILL reactor in Grenoble. By using a highly efficient HPGe array, coincidences between gamma-rays prompt with the fission event and those delayed up to several tens of microseconds were investigated, allowing to observe, for the first time, high-spin excited states above the 16.6 micros isomer. Lifetimes analysis, performed by fast-timing techniques with LaBr3(Ce) scintillators, reveals a difference of almost two orders of magnitude in B(M1) strength for transitions between positive-parity medium-spin yrast states. The data are interpreted by a newly developed microscopic model which takes into account couplings between core excitations (both collective and non-collective) of the doubly magic nucleus 132Sn and the valence proton, using the Skyrme effective interaction in a consistent way. The results point to a fast change in the nature of particle-core excitations with increasing spin.
Highlights
The γ -ray decay of excited states of the one-valence-proton nucleus 133Sb has been studied using coldneutron induced fission of 235U and 241Pu targets, during the EXILL campaign at the ILL reactor in Grenoble
The data are interpreted by a newly developed microscopic model which takes into account couplings between core excitations of the doubly magic nucleus 132Sn and the valence proton, using
Ideal systems to investigate this duality should be nuclei composed of one valence particle and a doubly magic core in which the coupling between collective core excitations and the valence nucleon strongly influences the structure of the system [1]
Summary
By using a highly efficient HPGe array, coincidences between γ -rays prompt with the fission event and those delayed up to several tens of microseconds were investigated, allowing to observe, for the first time, high-spin excited states above the 16.6 μs isomer. Taking into account the decay branchings from the two levels [33], B(M1) values were extracted for the 15/2+ → 13/2+ and 13/2+ → 11/2+ transitions, yielding > 0.24 W.u. and 0.0042(15) W.u., respectively This large difference, of almost two orders of magnitude, is clearly intriguing and brings a signature of some non-trivial change of configuration mixing in the 11/2+, 13/2+ and 15/2+ states of 133Sb. In order to interpret the experimental findings, a new microscopic model has been developed with the aim of describing states with different degrees of collectivity. Our calculation has no free parameters and is self-consistent in the sense that both single-particle states and phonons come out
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