Lifetime measurements of excited states in 169,171,173Os : Persistence of anomalous B(E2) ratios in transitional rare earth nuclei in the presence of a decoupled i13/2 valence neutron

Lifetimes of low-lying excited states in the νi13/2+ bands of the neutron-deficient osmium isotopes 169,171,173Os have been measured for the first time using the recoil-distance Doppler shift and recoil-isomer tagging techniques. An unusually low value is observed for the ratio B(E2; 21/2+ →17/2+)/B(E2; 17/2+ → 13/2+) in 169Os, similar to the “anomalously” low values of the ratio B(E2; 41+ → 21+)/B(E2; 21+ → 0+gs) previously observed in several transitional rare-earth nuclides with even numbers of neutrons and protons, including the neighbouring 168,170Os. Furthermore, the evolution of B(E2; 21/2+ → 17/2+)/B(E2; 17/2+ → 13/2+) with increasing neutron number in the odd-mass isotopic chain 169,171,173Os is observed to follow the same trend as observed previously in the even-even Os isotopes. These findings indicate that the possible quantum phase transition from a seniority conserving structure to a collective regime as a function of neutron number suggested for the even-even systems is maintained in these odd-mass osmium nuclei, with the odd valence neutron merely acting as a “spectator”. As for the even-even nuclei, the phenomenon is highly unexpected for nuclei that are not situated near closed shells.peerReviewe

Lifetime measurements of excited states in 163W and the implications for the anomalous B(E2) ratios in transitional nuclei

© 2019 The Authors This letter reports lifetime measurements of excited states in the odd-N nucleus 163W using the recoil-distance Doppler shift method to probe the core polarising effect of the i13/2 neutron orbital on the underlying soft triaxial even-even core. The ratio B(E2:21/2+→17/2+)/B(E2:17/2+→13/2+) is consistent with the predictions of the collective rotational model. The deduced B(E2) values provide insights into the validity of collective model predictions for heavy transitional nuclei and a geometric origin for the anomalous B(E2) ratios observed in nearby even-even nuclei is proposed

Decay spectroscopy of <math><mmultiscripts><mi>Os</mi><mprescripts/><none/><mrow><mn>171</mn><mo>,</mo><mn>172</mn></mrow></mmultiscripts></math> and <math><mmultiscripts><mi>Ir</mi><mprescripts/><none/><mrow><mn>171</mn><mo>,</mo><mn>172</mn><mo>,</mo><mn>174</mn></mrow></mmultiscripts></math>

International audienceWe report on a study of the α-decay fine structure and the associated Eα-Eγ correlations in the decays of Os171,172 and Ir171,172,174. In total, 13 new α-decay energy lines have been resolved, and three new γ-ray transitions have been observed following the new decay branches to Re168 and W167. The weak α-decay branch from the bandhead of the νi13/2 band in Os171 observed in this work highlights an unusual competition between α, β, and electromagnetic decays from this isomeric state. The nucleus Os171 is therefore one of few nuclei observed to exhibit three different decay modes from the same excited state. The nuclei of interest were produced in Mo92(Kr83,xpyn) fusion-evaporation reactions at the Accelerator Laboratory of the University of Jyväskylä, Finland. The fusion products were selected using the gas-filled ion separator RITU and their decays were characterized using an array of detectors for charged particles and electromagnetic radiation known as GREAT. Prompt γ-ray transitions were detected and correlated with the decays using the JUROGAM II germanium detector array surrounding the target position. Results obtained from total Routhian surface (TRS) calculations suggest that α-decay fine structure and the associated hindrance factors may be a sensitive probe of even relatively small shape changes between the final states in the daughter nucleus