Level densities and radiative strength functions in ${}^{171}\mathrm{Yb}$ and ${}^{170}\mathrm{Yb}$ nuclei have been measured using the ${}^{171}\mathrm{Yb}({}^3\mathrm{He},{}^3\mathrm{He}^{\prime }\gamma ){}^{171}\mathrm{Yb}$ and ${}^{171}\mathrm{Yb}({}^3\mathrm{He},\alpha \gamma ){}^{170}\mathrm{Yb}$ reactions. New data on ${}^{171}\mathrm{Yb}$ are compared to previous measurements for ${}^{171}\mathrm{Yb}$ from the ${}^{172}\mathrm{Yb}({}^3\mathrm{He},\alpha \gamma ){}^{171}\mathrm{Yb}$ reaction. The systematics of level densities and radiative strength functions in ${}^{170,171,172}\mathrm{Yb}$ are established. The entropy excess in ${}^{171}\mathrm{Yb}$ relative to the even-even nuclei ${}^{170,172}\mathrm{Yb}$ due to the unpaired neutron quasiparticle is found to be approximately $2k_B$. Results for the radiative strength function from the two reactions lead to consistent parameters characterizing the “pygmy” resonances. Pygmy resonances in the ${}^{170,172}\mathrm{Yb}$ populated by the $({}^3\mathrm{He},\alpha )$ reaction appear to be split into two components for both of which a complete set of resonance parameters is obtained.

• Received 23 July 2004

DOI:https://doi.org/10.1103/PhysRevC.70.054611