Proton bombardment of pure ${\mathrm{Tm}}_2$${\mathrm{O}}_3$, followed by ion-exchange separations, has yielded an activity with an 18.5-minute half-life. Determination of the excitation function and identification of the daughter ${\mathrm{Tm}}^{167}$ assigns the activity to ${\mathrm{Yb}}^{167}$. A gamma-ray spectrum shows it to decay by electron capture with a 0.118 Mev and possibly other gamma rays.

• Received 27 January 1954

DOI:https://doi.org/10.1103/PhysRev.94.968