Alpha-Decay Properties of Some Thulium and Ytterbium Isotopes Near the 82-Neutron Closed Shell

The 84- and 85-neutron isotopes of Tm and Yb were produced by heavy-ion reactions on neutron-deficient rare-earth targets. These isotopes, which are 16 to 18 neutrons removed from the beta stability line, decay predominantly by alpha-particle emission. A search was made for proton emission in the decay of these nuclides and in ${\mathrm{Tm}}^{151}$ and ${\mathrm{Tm}}^{152}$, but none was observed. The alpha-decay properties of these nuclides were measured and compared with the systematics of alpha decay of the 84- and 85-neutron isotopes. Evidence was obtained for the existence of a long-lived alpha-emitting isomeric state in ${\mathrm{Tm}}^{154}$.