Two-particle two-hole configurations inBi208and theBim210(p,t)Bi208reaction

Abstract

Levels in $^{208}\mathrm{Bi}$ were studied using the $^{210}\mathrm{Bi}^{m}(p,t)^{208}\mathrm{Bi}$ reaction at 18.4 MeV. The target isomeric state employed in the reaction was the ${9}^{\ensuremath{-}}$, 271 keV, 3 \ifmmode\times\else\texttimes\fi{} ${10}^{6}$ year second-excited state of $^{210}\mathrm{Bi}$. The measured angular distributions for the positive parity ($\ensuremath{\pi}{h}_{\frac{9}{2}}$,${\ensuremath{\nu}}^{\ensuremath{-}1}$) particle-hole multiplets were well described by distorted-waves calculations using the shell model wave functions of Kuo. However, the data for the negative parity ($\ensuremath{\pi}{h}_{\frac{9}{2}}$,${\ensuremath{\nu}}^{\ensuremath{-}1}{i}_{\frac{13}{2}}$) levels were poorly reproduced by these calculations, and evidence was found for the presence of two-particle two-hole admixtures in the ${9}^{\ensuremath{-}}$, ${10}^{\ensuremath{-}}$, and ${11}^{\ensuremath{-}}$ members of this multiplet. In addition, a number of previously unobserved levels were identified in $^{208}\mathrm{Bi}$, and several of these were populated in the reaction with considerably enhanced cross sections. The excitation energies and differential cross sections for the latter group of levels were found to be characteristic of two-particle two-hole states in $^{208}\mathrm{Bi}$ consisting of $\ensuremath{\pi}{h}_{\frac{9}{2}}$, $\ensuremath{\nu}{g}_{\frac{9}{2}}$ particles coupled to the ${0}_{1}^{+}$ and ${2}_{1}^{+}$ excitations of $^{206}\mathrm{Pb}$.NUCLEAR REACTIONS $^{210}\mathrm{Bi}^{m}(p,t)^{208}\mathrm{Bi}$, $E=18.4$ MeV; measured $\ensuremath{\sigma}(\ensuremath{\theta})$. $^{208}\mathrm{Bi}$ deduced levels, $J$, $\ensuremath{\pi}$. Radioactive, enriched target. DWBA analysis, tested shell model wave functions.