- D. Ackermann, GSI Helmholtzzentrum für Schwerionenforschung GmbH

Thursday, June 6, 11:00 AM - Research Discussion

NSCL Lecture Hall

The spherical shell stabilized superheavy elements (SHE) predicted at the extreme of high Z and A are a nuclear structure phenomenon. They owe their existence to shell effects, an energy contribution of quantum mechanical origin to the nuclear potential, without which they would not be bound. Experimental activities in this field, apart from attempts to directly synthesize new elements, have to investigate reaction mechanism studies and, in particular, they have to pursue nuclear structure investigations to study the development of single particle levels towards the expected gap for the proton (at Z = 114, 120 or 126) and neutron (at N = 184) shell closures in the region of the spherical SHE. A number of exciting results in terms of the synthesis of new elements [1,2,3] have lead us at the border of that region. In particular, the results obtained at the Flerov Laboratory of Nuclear Reactions (FLNR) for a rich number of decay patterns for 48Ca induced reactions on actinide targets [2] have by now been confirmed GSI [4,5,6], and LBNL [7]. Efficient experimental set-ups, including separators and advanced particle and photon detection arrangements, allow for detailed nuclear structure studies for nuclei at and beyond Z=100. A review of recent achievements is given in ref. [8]. Among the most interesting features is the observation of K-isomeric states, partly also as a tool to track the development of deformation towards the spherical SHE. The heaviest example for such a nuclear structure feature was found in 270Ds. In a recent experiment we could extend the knowledge on this nucleus and its decay products largely. For 266Hs we detected the sf branch with a surprisingly large branching ratio of 0.24 0.09, and revealed strong indications for a K-isomer for the first Z=108 isotope. The α-decay branch found in 262Sg establishes the missing link to 254No for which we measured a precise mass value with SHIPTRAP [9], yielding an experimental mass value for the whole decay chain up to 270Ds, an anchor point for theoretical models in mass and binding energy for the heaviest nuclei. These new results, their implications for the superheavy element research and the future perspectives of the field including the possible use of rare isotope beams will be discussed. References [1] S. Hofmann and G. Münzenberg, Rev. Mod. Phys. 72, 733 (2000). [2] Yu.Ts. Oganessian, J. Phys. G 34, R165 (2007). [3] K. Morita et al., J. Phys. Soc. Jpn. 73, 2593 (2004). [4] S. Hofmann et al., Eur. Phys. J. A 32, 251 (2007). [5] C.E. Düllmann et al, Phys. Rev. Lett. 104, 252701 (2010). [6] S. Hofmann et al., EPJ A 48, 62 (2012). [7] L. Stavstera, Phys. Rev. Lett. 103, 132502 (2009). [8] R.-D. Herzberg and P.T. Greenlees, Prog. Part. Nuc. Phys. 61, 674 (2008). [9] M. Block et al., Nature 463, (2010) 785.