B. Andel

The K -isomeric states in the heaviest nuclei are among the interesting topics in superheavy-element research. In the present work, we report on the discovery of µ s isomers in Sg 258 , 259 , 260 which deexcite with half-lives of 120 − 55 + 578 µ s , 85 ± 6 µ s , and 8 . 5 − 1.8 + 3.1 µ s , respectively, and are attributed to high- K states formed in multiquasiparticle couplings. In Sg 261 , activity with 12 . 6 − 1.6 + 2.2 µ s half-life was observed and it is suggested to originate from decays of a high- K multiquasiparticle and/or single-particle isomeric states.

The production of Os 159 , 160 , 161 and Re 159 , 160 , 161 was investigated in experiments performed at the Accelerator Laboratory of the University of Jyväskylä. The nuclei of interest were produced using fusion-evaporation reactions induced by beams of 275–353 MeV Ni 58 ions bombarding a Cd 106 target. The evaporation residues were separated in flight using the recoil separator MARA and implanted into a double-sided silicon strip detector, which was used to measure their decays. Cross sections for the production of these nuclides were measured and the relative population of the 8 + isomeric states and ground states of the N =84 isotones Hf 156 , W 158 , and Os 160 were deduced. New decay chains assigned to Os 160 were identified at beam energies of 310 and 330 MeV. These findings are compared with previous studies claiming the observation of Os 160 and W 156 . The α decays of Os 161 were observed, confirming previous results for this nuclide and its β -decaying daughter, W 157 . The α -decay branch of Re 159 was also confirmed, but no delayed decays of this nuclide were observed that would be a signature of the β decays of the as yet unknown nuclide Os 159 .

A search for a β -delayed fission ( β DF ) decay branch of isomerically pure samples of Au g 178 and Au m 178 was performed at the ISOLDE-CERN facility. Two complementary detection systems capable of registering α decays and fission fragments, the ISOLDE Decay Station and the ASET (Alpha SETup), were used. Despite very high statistics of produced Au 178 nuclei, no fission fragments were detected. Upper limits of β DF probabilities of P β DF ( Au g 178 ) < 1.11 ( 2 ) × 10 − 8 and P β DF ( Au m 178 ) < 9.7 ( 2 ) × 10 − 9 were determined. Corresponding lower limits of β DF partial half-lives were deduced as well, and the results are discussed in the context of experimental systematics of β DF in the neutron-deficient region of the nuclear chart.

The changes in the mean-squared charge radii relative to Bi 126 209 ( δ 〈 r 2 〉 N , 126 ) and the magnetic dipole and electric quadrupole moments in Bi 214 − 218 have been measured using the in-source resonance-ionization spectroscopy technique at ISOLDE (CERN). Magnetic moments of odd-odd bismuth nuclei have been analyzed by the additivity relation. Previous tentative spin-parity and configuration assignments based on the β -decay feeding patterns have been supported. A normal odd-even staggering in charge radii of bismuth isotopes with N > 126 has been observed. The new data for the δ 〈 r 2 〉 of bismuth isotopes allow a study of the isotonic dependencies in the charge radii, revealing jumps in δ 〈 r 2 〉 132 , 126 and δ 〈 r 2 〉 134 , 126 at Z = 84 . This pattern could be explained by a sudden onset of octupole deformation at N = 132 and 134 when going from polonium ( Z = 84 ) to astatine ( Z = 85 ).

An α - and β -decay study of a pure source of laser-ionized and mass-separated Au 182 ( Z = 79, N = 103) was carried out at the ISOLDE Decay Station at the ISOLDE-CERN facility. Detailed γ − γ analysis following EC / β + decay of Au 182 was performed, and the level scheme of daughter nuclide Pt 182 was considerably extended via the identification of 125 new levels and 336 new γ -ray transitions. The nonexistence of a relatively long-lived isomeric state in Au 182 and influence of the pandemonium effect on β -decay feeding intensities are discussed. Differences in feeding for two coexisting bands in Pt 182 were investigated. The α -decay scheme of Au 182 was extended and an α -decay branching ratio of 0.129 ( 11 ) % was measured. Hindrance factors for α -decay branches were calculated and I π = ( 1 + , 2 + , 3 + ) assignment for the Ir 178 ground state was proposed.

The process of β -delayed fission ( β DF ) of Fr 230 , 232 and Ac 230 , 232 , 234 was studied in an experiment performed at the ISOLDE facility at CERN. As no fission fragments were observed for any of the nuclei investigated, upper limits for their β DF probability ( P β DF ) were determined. The experimental results were compared with theoretical calculations that were first benchmarked on Tl 178 , 180 P β DF experimental values. The P β DF values were calculated using the code TALYS to which β -strength functions obtained from the D1M Gogny parametrization and from the Skyrme functional SKO' were given as input together with fission paths obtained with BSkG3 and BSk14 models. Sensitivity studies of different β -strength functions, and fission paths scaling on the P β DF values were conducted, suggesting a stronger dependence of the P β DF on the fission paths rather than on the β -strength function used. Published by the American Physical Society 2025

Polonium isotopes having two protons above the shell closure at Z = 82 show a wide variety of low-lying, high-spin isomeric states across the whole chain. The structure of neutron-deficient isotopes up to Po 210 ( N = 126 ) is well established as they are easily produced through various methods. However, there is not much information available for the neutron-rich counterparts for which only selective techniques can be used for their production. We report on the first fast-timing measurements of yrast states up to the 8 + level in Po 214 , 216 , 218 isotopes produced in the β − decay of Bi 214 , 216 , 218 at ISOLDE, CERN. In particular, our new half-life value of 607(14) ps for the 8 1 + state in Po 214 is nearly 20 times shorter than the value available in the literature and comparable with the newly measured half-lives of 409(16) and 628(25) ps for the corresponding 8 1 + states in Po 216 , 218 , respectively. The measured B ( E 2 ; 8 1 + → 6 1 + ) transition probability values follow an increasing trend relative to isotope mass, reaching a maximum for Po 216 . The increase contradicts the previous claims of isomerism for the 8 + yrast states in neutron-rich Po 214 and beyond. Together with the other measured yrast transitions, the B ( E 2 ) values provide a crucial test of the different theoretical approaches describing the underlying configurations of the yrast band. The new experimental results are compared to shell-model calculations using the KHPE and H208 effective interactions and their pairing-modified versions, showing an increase in configuration mixing when moving toward the heavier isotopes.