ESTIMATION OF THE TIME-SCALE OF LAST CHANCE ALPHA-EMISSION USING AN ATOMIC CLOCK

The probability of filling a K-vacancy, created on the incoming part o f the collision, before alpha-particle emission is used to time the de cay of Yb compound nuclei. These nuclei were produced in the fusion re action 250 MeV Ni-60 + Mo-100. In general the nuclear decays are too f ast to be timed by this clock, however, alpha-particle emitting compou nd nucleus states have lifetimes sufficiently long for this technique to work when both the alpha-particle has low energy and the compound n ucleus spin is large. This supports the existence of last, or near las t, chance alpha-particle emission in the deexcitation of high spin com pound nuclei.