Fission of superheavy nuclei: Fragment mass distributions and their dependence on excitation energy

The mass and total kinetic energy distributions of the fission fragments in the fission of even-even isotopes of superheavy elements from Hs (Z = 108) to Og (Z = 118) are estimated using a prescission point model. We restrict to nuclei for which spontaneous fission has been experimentally observed. The potential energy surfaces are calculated with Strutinsky's shell correction procedure. The parametrization of the nuclear shapes is based on Cassini ovals. For the just-before-scission configuration we fix alpha = 0.98, which corresponds to r(neck) approximate to 2 fm, and take into account another four deformation parameters: alpha(1), alpha(3), alpha(4), alpha(6). The fragment-mass distributions are estimated supposing they are due to thermal fluctuations in the mass asymmetry degree of freedom just before scission. The influence of the excitation energy of the fissioning system on these distributions is studied. The distributions of the total kinetic energy (TKE) of the fragments are also calculated (in the point-charge approximation). In Hs, Ds, and Cn isotopes a transition from symmetric to asymmetric fission is predicted with increasing neutron number N (at N approximate to 168). Supersymmetric fission occurs at N approximate to 160. When the excitation energy increases from 0 to 30 MeV, the peaks (one or two) of the mass distributions become only slightly wider. The first two moments of the TKE distributions are displayed as a function of the mass number A of the fissioning nucleus. A slow decrease of the average energy and a minimum of the width (at N approximate to 162) is found.