Production of neutron-rich Bi isotopes by transfer reactions

Abstract

Production of neutron-rich Bi isotopes was investigated by irradiating Hg, Tl, and Pb targets with $^{18}\mathrm{O}$ ions in the 5-10 MeV/nucleon range. Following irradiation, bismuth was chemically separated and the yields of $^{211\ensuremath{-}213}\mathrm{Bi}$ isotopes were determined via $\ensuremath{\alpha}$-emitting Po daughters. Effective residual transfers of $^{3\ensuremath{-}5}\mathrm{H}$ to $^{208}\mathrm{Pb}$, $^{7,8}\mathrm{He}$ to $^{205}\mathrm{Tl}$, and $^{8}\mathrm{Li}$ to $^{204}\mathrm{Hg}$ were observed. Cross sections generally peaked in the 7-8 MeV/nucleon region and ranged from a high of \ensuremath{\sim}2 mb for $^{3}\mathrm{He}$ absorption to \ensuremath{\sim}0.6 nb for $^{8}\mathrm{He}$ absorption. Total $\ensuremath{\alpha}$- and $\ensuremath{\beta}$-decay branches of the ${J}^{\ensuremath{\pi}}={9}^{\ensuremath{-}},25$ min isomer of $^{212}\mathrm{Bi}$ were measured to be 67% and 33%, respectively, (3.2\ifmmode\pm\else\textpm\fi{}0.2)% of the decays being associated with $\ensuremath{\beta}$-delayed $\ensuremath{\alpha}$-particle emission. Production yields for the ${J}^{\ensuremath{\pi}}={1}^{\ensuremath{-}}$ ground state and ${9}^{\ensuremath{-}}$ and ${15}^{\ensuremath{-}}$ isomeric levels for $^{212}\mathrm{Bi}$ were extracted. The ratio of isomeric states to the ground state increased by more than two orders of magnitude over the energy range studied. However, the maximum value of the cross section ratio $\frac{\ensuremath{\sigma}({J}^{\ensuremath{\pi}}={15}^{\ensuremath{-}})}{\ensuremath{\sigma}({J}^{\ensuremath{\pi}}={9}^{\ensuremath{-}})}$ was only 0.04, implying a low angular momentum transfer. The reactions were analyzed using the Wilczy\ifmmode \acute{n}\else \'{n}\fi{}ski sum rule, which gave a rather poor fit to the results with respect to both the yield and the implied angular momentum transfer. The observed relatively high cross sections, modest angular momentum transfer, and broad excitation functions indicate that transfer processes provide a viable method for reaching neutron-rich nuclides in the heavy element region.