The electron-capture decay of the ${}^{168}{\mathrm{Lu}}^m$ ${(T}_{1/2}=6.7\mathrm{}\hspace{0.5em}\min ,$ $J^{\pi }{=3\mathrm{}}^{+})$ isomer was studied with high purity sources, obtained by using a new radiochemical method consisting of fast continous on-line separation of reaction products. A complex spectrum composed of about 200 $\gamma$ rays was observed. From these, 162 transitions were assigned to a level scheme of 39 excited levels of ${}^{168}\mathrm{Yb}$, primarily by $\gamma -\gamma$ coincidence spectroscopic measurements. About 60 transitions were placed for the first time and $>90\%$ of the decay intensity was clearly identified. The structure of the levels directly fed by the electron-capture decay was reviewed as particle-hole excitations of the core.

• Received 18 February 1999

DOI:https://doi.org/10.1103/PhysRevC.60.024304