A New Type of Asymmetric Fission in Proton-Rich Nuclei (The curios case of beta-delayed fission of 180Tl)
by
Andrei ANDREYEV(University of the West of Scotland, Paisley, UK)
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Description
Beta-delayed (EC/β+,β-) 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 presentation, I will discuss the results of a recent detailed 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.
We claim the discovery of a new, non-fragment-shell-driven, asymmetric fission mode. By calculating the potential surface as a function of five shape variables, we establish that subtle microscopic effects near the saddle, clearly not related to fragment structure, drive the system to asymmetric fission.
*On behalf of Paisley-Leuven-Los-Alamos-Bratislava-Darmstadt-Geneva-Gent-Grenoble-Liverpool-Manchester-Orsay-Tokai collaboration