Anatoly E. Barzakh

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.

Electronic factors for the field and mass isotope shifts in the 6p ²P_3/2 → 7s ²S_1/2 (535 nm), 6p ²P_1/2 → 6d ²D_3/2 (277 nm) and 6p ²P_1/2 → 7s ²S_1/2 (378 nm) transitions in the neutral thallium were calculated within the high-order relativistic coupled cluster approach. These factors were used to reinterpret previous experimental isotope shift measurements in terms of charge radii of a wide range of Tl isotopes. Good agreement between theoretical and experimental King-plot parameters was found for the 6p ²P_3/2 → 7s ²S_1/2 and 6p ²P_1/2 → 6d ²D_3/2 transitions. It was shown that the value of the specific mass shift factor for the 6p ²P_3/2 → 7s ²S_1/2 transition is not negligible compared to the value of normal mass shift in contrary to what had been suggested previously. Theoretical uncertainties in mean square charge radii were estimated. They were substantially reduced compared to the previously ascribed ones and amounted to less than 2.6%. The achieved accuracy paves the way to a more reliable comparison of the charge radii trends in the lead region.