The decay properties of ${}_{}{}^{153}{}_{}{}^{}\mathrm{Yb}$ and ${}_{}{}^{153}{}_{}{}^{}\mathrm{Tm}$, produced in ${}_{}{}^{64}{}_{}{}^{}\mathrm{Zn}$ bombardments of ${}_{}{}^{92}{}_{}{}^{}\mathrm{Mo}$, were investigated following on-line mass separation. A decay scheme, incorporating 34 transitions and 25 levels in ${}_{}{}^{153}{}_{}{}^{}\mathrm{Tm}$, was constructed for ${}_{}{}^{153}{}_{}{}^{}\mathrm{Yb}$. It establishes the $s_{1/2}$ proton level in ${}_{}{}^{153}{}_{}{}^{}\mathrm{Tm}$ to be isomeric at an excitation energy of 43.2 keV. The α-decay branch of the $h_{11/2}$ ${}_{}{}^{153}{}_{}{}^{}\mathrm{Tm}$ ground state was determined to be 91±3%. In addition, a partial decay scheme was put together for the 9% ${\beta }^{+}$ branch. About 66% of this ${\beta }^{+}$ decay proceeds to the $h_{9/2}$ neutron state located at 299.3 keV in ${}_{}{}^{153}{}_{}{}^{}\mathrm{Er}$. Only one transition, 266.5 keV, could be assigned to the ${\beta }^{+}$ decay of the ${}_{}{}^{153}{}_{}{}^{}\mathrm{Tm}$ $s_{1/2}$ isomer; it is suggested that the γ ray deexcites the $p_{3/2}$ neutron level to the $f_{7/2}$ ${}_{}{}^{153}{}_{}{}^{}\mathrm{Er}$ ground state. Based on the intensity of this 266.5-keV γ ray, the isomer’s α branch was estimated to be ∼93%.

• Received 26 September 1988

DOI:https://doi.org/10.1103/PhysRevC.39.636