Background: Levels fulfilling the seniority scheme and relevant isomers are commonly observed features in semimagic nuclei; for example, in Sn isotopes (Z = 50). Seniority isomers in Sn, with dominantly pure neutron configurations, directly probe the underlying neutron-neutron (νν) interaction. Furthermore, an addition of a valence proton particle or hole, through neutron-proton (νπ) interaction, affects the neutron seniority as well as the angular momentum.
Lifetimes of the excited states in the neutron-rich 52,54 Ti nuclei, produced in a multinucleon-transfer reaction, were measured by employing the Cologne plunger device and the recoil-distance Doppler-shift method. The experiment was performed at the Grand Accélérateur National d'Ions Lourds facility by using the Advanced Gamma Tracking Array for the γ-ray detection, coupled to the large-acceptance variable mode spectrometer for an event-by-event particle identification. A comparison between the transition probabilities obtained from the measured lifetimes of the 2 + 1 to 8 + 1 yrast states in 52,54 Ti and that from the shell-model calculations based on the
Lifetime measurements of excited states of the light N ¼ 52 isotones 88 Kr, 86 Se, and 84 Ge have been performed, using the recoil distance Doppler shift method and VAMOS and AGATA spectrometers for particle identification and gamma spectroscopy, respectively. The reduced electric quadrupole transition probabilities BðE2; 2 þ → 0 þ Þ and BðE2; 4 þ → 2 þ Þ were obtained for the first time for the hard-to-reach 84 Ge. While the BðE2; 2 þ → 0 þ Þ values of 88 Kr, 86 Se saturate the maximum quadrupole collectivity offered by the natural valence (3s, 2d, 1g 7=2 , 1h 11=2) space of an inert 78 Ni core, the value obtained for 84 Ge largely exceeds it, suggesting that shape coexistence phenomena, previously reported at N ≲ 49, extend beyond N ¼ 50. The onset of collectivity at Z ¼ 32 is understood as due to a pseudo-SU(3) organization of the proton single-particle sequence reflecting a clear manifestation of pseudospin symmetry. It is realized that Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.
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