Onset of deformation in neutron-deficient Bi isotopes studied by laser spectroscopy

Abstract

In-source laser spectroscopy experiments for bismuth isotopes at the 306.77-nm atomic transition has been carried out at the Investigation of Radioactive Isotopes on Synchrocyclotron facility of Petersburg Nuclear Physics Institute. New data on isotope shifts and hyperfine structure for Bi ground states and isomers $(^{189,190\mathrm{m}1,190\mathrm{m}2,191,192,192\mathrm{m},194,194\mathrm{m},198\mathrm{m}}\mathrm{Bi})$ have been obtained. The changes in the mean-square charge radii $\ensuremath{\delta}\ensuremath{\langle}{r}^{2}\ensuremath{\rangle}$ and magnetic-moment values have been deduced. For Bi nuclei a marked deviation from the isotopic trend of $\ensuremath{\delta}\ensuremath{\langle}{r}^{2}\ensuremath{\rangle}$ in lead and thallium isotopic chains has been demonstrated at $N\phantom{\rule{0.16em}{0ex}}l\phantom{\rule{0.16em}{0ex}}111$. This has been interpreted as an indication of the onset of quadrupole deformation. Analysis of the magnetic moments for odd-odd Bi isotopes also points to the possible increase in deformation at $N\phantom{\rule{0.16em}{0ex}}l\phantom{\rule{0.16em}{0ex}}111$.