Charge radii and electromagnetic moments of 214-218Bi: Exploring the "southern" border of the Z > 82 octupole-deformation region

Abstract

The changes in the mean-squared charge radii relative to 209Bi126 (δ(r 2) N,126), the magnetic dipole and electric quadrupole moments in214−218Bi have been measured using the in-source resonanceionization 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(r2)132,126 and δ(r2)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).