Fission mass yields of excited medium-heavy nuclei studied within the fragmentation theory - the 172Yb system as an example

The mass distributions resulting from the fission of excited medium-heavy nuclei are discussed on the basis of the fragmentation theory. It is shown that very asymmetric fission events can be expected with rates which are only a few orders of magnitude smaller than the rates for symmetric fission. As an example a calculation of the fission mass distribution of the excited 172Yb compound nucleus is presented. This mass distribution reveals observable structures over the entire range of the mass asymmetry due to valleys in the potential energy surface for fission fragments with closed proton and neutron shells. (author)