Search for. cap alpha. -decay of high spin isomers in rare earth nuclei

Using a decay-in-flight technique, a search for 1--100 nsec ..cap alpha.. decay has been conducted in a variety of rare earth nuclei made in energetic heavy ion reaction. Assuming spherical rigid rotation and ..cap alpha.. particle formation factors similar to those of the ground state, this lifetime range corresponds to nuclear spins of 30 --50 h-bar where very high spin isomerism has been predicted theoretically. No evidence for ..cap alpha.. decay was observed. ..cap alpha.. decay cross section limits are set for 14 systems in which high spin isomers (I>10 h-bar) are known with lifetimes in the range studied. Comparison to theoretical total cross sections allows ..cap alpha..-branching ratio estimates to be made.