APH N.S., Heavy Ion Physics 18/2–4 (2003) 331–332 HEAVY ION PHYSICS c Akad´ emiai Kiad´ o Relationship between Hyperdeformation, Fission Resonances and Clustering in 233 Th N. Nenoff, 1 H. Beer, 2 P. Bringel, 1 S. Chmel, 1 M. Csatl´ os, 3 S. Dababneh, 2 M. Heil, 2 H. H¨ ubel, 1 F. K¨ appeler, 2 A. Krasznahorkay, 3 E. Mergel, 1 R. Plag 2 and R. Reifarth 2 1 Helmholtz-Institut f¨ ur Strahlen- und Kernphysik, Univ. Bonn D-53115 Bonn, Germany 2 Forschungszentrum Karlsruhe, Institut f¨ ur Kernphysik D-76021 Karlsruhe, Germany 3 Institute of Nuclear Research of the Hungarian Academy of Science H-4001 Debrecen, Hungary Received 10 January 2003 Abstract. The mass distribution of nuclides produced in the reaction 232 Th(n,f) with neutron energies below and within the resonance region was investigated using the activation method. The results confirm the theoretical predictions of the existence of hyperdeformed octupole shapes in 233 Th. Keywords: fission resonances, hyperdeformation, cluster states in nuclei PACS: 25.85.Ec, 24.30.-v, 21.10.Gv, 21.60.Gx, 27.90.+b High-precision measurements of fission resonances [1–3] in the actinide region show structures that have been interpreted as excited states in a hyperdeformed (HD) potential-energy minimum. In 233 Th two broad fission resonances were observed already 45 years ago in excitation functions of neutron-induced fission of 232 Th at neutron energies around 1.6 and 1.7 MeV (Refs. cited in [3]). Recent experimental investigations of the 232 Th(n,f) and 232 Th(d,pf) reactions [3] with better energy resolution show that these two broad resonances split into several narrow resonances which can be associated with rotational band structures with alternating parity built on vibrational states in the third minimum. The appearance of alternating-parity bands in 233 Th suggests a pear-like HD shape. Minima with a large stable octupole shape have been predicted theoretically by Nilsson–Strutinsky calculations [4]. The HD octupole shape is stabilized by shell effects, resulting in a two-cluster system of the doubly-magic nucleus 132 Sn and a deformed nucleus, e.g. 100 Zr. In an alternative approach, it was suggested [5] that a HD di-nuclear configuration can be formed in 232 Th. 1219-7580/03/ $ 20.00 c  2003 Akad´ emiai Kiad´ o, Budapest