  The rearrangement step of nuclear fission occurs within 0.17 yoctosecond, in
a new state of nuclear matter characterized by the formation of closed shells
of nucleons. The determination of its lifetime is now based on the prompt
neutron emission law. The width of isotopic distributions measures the
uncertainty in the neutron number of the fragments. Magic mass numbers, 82 and
126, play a major role in the mass distributions. Arguments are presented in
favour of an all-neutron state. The boson field responsible for the new
collective interaction has to be searched for.
