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Beta-Delayed Fission in the Lead Region (The curios case of beta-delayed fission of 180Tl)

Andrei Andreyev, University of the West of Scotland, Paisley, UK
Vendredi 17 Septembre 2010 à 10h30 - Salle des Séminaires

Beta-delayed (EC/b+,b-) fission is a rare nuclear decay process in which the beta-decaying parent nuclide populates excited states in its daughter, which may then fission. In the first part of the talk, general features of nuclear fission and, in particular, of the beta-delayed fission will be discussed. This will be followed by a detailed presentation of the results of a recent fission study of the very neutron-deficient nucleus 180Hg, which possesses an unusual neutron-to-proton ratio of N/Z=1.25 (to be compared to N/Z=1.56 for the actinide region where most of the previous fission studies have been performed). The result was obtained in a study of the beta-delayed fission of 180Tl at ISOLDE(CERN). A novelty and key feature of this work was the production of a pure source of 180Tl using resonant laser ionization with subsequent mass separation by ISOLDE. In a strong contrast to generally accepted approaches, the fragment mass distribution of 180Hg is asymmetric. This asymmetry is even more surprising as a mass symmetric split of 180Hg would lead to two 90Zr fragments, with magic N=50 and semi-magic Z=40. Newest results on the beta-delayed fission of several other nuclei in this region of the Nuclide Chart will be presented.

*On behalf of Paisley-Leuven-Los-Alamos-Bratislava-Darmstadt-Geneva-Gent-Grenoble-Liverpool-Manchester-Orsay-Tokai collaboration