Coulomb Excitation ofBi209and the Weak-Coupling Model

Abstract

Some relative and absolute $\gamma$-ray transition probabilities have been measured for the low-lying levels in ${}_{}{}^{209}{}_{}{}^{}\mathrm{Bi}$ by observing the Coulomb excitation and subsequent decay of the states. Thick bismuth targets were bombarded with 19-MeV $\alpha$ particles, and $\gamma$-ray yields at 0°, 30°, 45°, 60°, and 90° were observed with a 25-${\mathrm{cm}}^3$ LiGe detector. Determinations have been made of the transition strengths to the $f_{\frac{7}{2}}$ (0.897-MeV), the $i_{\frac{13}{2}}$ (1.608-MeV), and the $f_{\frac{5}{2}}$ (2.822-MeV), and the septuplet of levels near 2.6 MeV, formed by coupling an $h_{\frac{9}{2}}$ particle to the $3^{-}$ octupole state in ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$, excited by $E2\mathrm{}$, $E3\mathrm{}$, $E2\mathrm{}$, and $E3\mathrm{}$ Coulomb excitation, respectively, Approximate $E1\mathrm{}$ transition strengths for ground-state decays of the 2.563-, 2.581-, and 2.598-MeV levels have been determined from the Doppler broadening of the $\gamma$ peaks. Branches are observed corresponding to decays from the 2.741- and 2.600-MeV states to the 1.608 (${\frac{13}{2}}^{+}$) level, and from the 2.822-, 2.615-, and 2.581-MeV levels to the 0.897 (${\frac{7}{2}}^{-}$) state. The $\gamma$-ray strengths and relative transition rates are compared with the predictions of a particle-vibration coupling model.