Strongly Enhanced Low Energy Alpha-Particle Decay in Heavy Actinide Nuclei and Long-Lived Superdeformed and Hyperdeformed Isomeric States

摘要

Relatively low energy and very enhanced alpha-particle groups have beenobserved in various actinide fractions produced via secondary reactions in aCERN W target which had been irradiated with 24-GeV protons. In particular,5.14, 5.27 and 5.53 MeV alpha-particle groups with corresponding half-lives of3.8(+ -)1.0 y, 625(+ -)84 d and 26(+ -)7 d, have been seen in Bk, Es and Lr-Nosources, respectively. The measured energies are a few MeV lower than the knowng.s. to g.s. alpha-decays in the corresponding neutron-deficient actinidenuclei. The half-lives are 4 to 7 orders of magnitude shorter than expectedfrom the systematics of alpha-particle decay in this region of nuclei. Thededuced evaporation residue cross sections are in the mb region, about 4 ordersof magnitude higher than expected. A consistent interpretation of the data isgiven in terms of production of long-lived isomeric states in the second andthird wells of the potential-energy surfaces of the parent nuclei, which decayto the corresponding wells in the daughters. The possibility that the isomericstates in the third minimum are actually the true or very near the true groundstates of the nuclei, and consequences regarding the production of thelong-lived superheavy elements, are discussed.