The A≈100 mass region is of special interest due to a rapid shape transition, observed by going from neutron number 58 to 60, especially pronounced in the Zr isotopes, where 98Zr is weakly and 100Zr is strongly deformed. To further examine this intricate phenomenon, in this work lifetimes of low-lying excited states in the nuclei 99Zr and 99Nb were determined using fast-timing techniques and an experimental setup consisting of four LaBr3(Ce) detectors. Neutron rich A=99 fragments were produced in neutron induced fission and separated by the spectrometer LOHENGRIN at the Institut Laue-Langevin in Grenoble, France. Experimental values are compared to two different calculations in the framework of the interacting boson-fermion model and discussed in the context of shape coexistence.

Lifetimes of the low-lying yrast states 2+,4+, and 6+ of the unstable nucleus 182Os were measured using digital fast-timing techniques. The lifetimes of the 4+ and 6+ states were determined for the first time. The remeasured value for the lifetime of the 2_1+ state was taken into account to evaluate the discrepancy between two inconsistent literature values. The lifetimes and extracted B(E2) values are presented and discussed in terms of collective signatures and transitional phenomena. The B(E2;4_1+→2_1+)/B(E2;2_1+→0_1+) ratio of 1.39(7) supports the interpretation of 182Os as a rigid rotor. This value is discussed in the context of these of the neighboring isotopes and isotones and calculations in the framework of the interacting boson model 1. Additionally, competing influences from the near lying collective deformed region,γ-soft rotors, X(5) symmetry, and neighboring regions of shape coexistence in low excitation states are assumed to influence the structure of the nucleus of interest: The trend of the excitation energies of the γ- and Kπ=0–bands in the osmium isotopic chain change remarkably at 182Os. This consideration helps to us delimit and understand the structural transitions in the isotopic and isotonic chains that intersect at 182Os.

Low-lying states in 206Po were investigated using the fast-timing technique with LaBr3(Ce) and high-purity germanium detectors. The excited states in this nucleus were populated via two consecutive electron capture decays from 206Rn. The parent isotope was produced in the 194Pt(16O,4n)206Rn fusion-evaporation reaction at the FN-Tandem facility at the Institute for Nuclear Physics, University of Cologne. The previously known value for the lifetime of the 4_1+ state in 206Po was confirmed using the generalized centroid difference (GCD) method. The lifetime of the 6_1+ state was determined from β decay in the first application of the GCD method for x-ray–γ coincidences. A Monte Carlo based approach was applied to address the indirect population of the 6_1+ state by the decay of 206At. The experimental results were examined in the context of the transition of single-particle excitations to collective behavior in the neutron-deficient Po isotopes. The obtained B(E2;6_1+→4_1+) value suggests that for the 6_1+ states in even-even Po isotopes the transition from a noncollective regime at N=126 to a collective regime occurs at N≤120.