Charge distributions of fission fragments of low- and high-energy fission of Fm, No, and Rf isotopes

The charge (mass) distributions of fission fragments resulting from low- and high-energy fission of the even-even nuclei Fm-254-260,Fm-264, No258-264, and (262-266)Rf are studied with the statistical scission-point model. The calculated results are compared with the available experimental data. In contrast to the experimental data, the calculated mass distribution for Fm-258(s.f.) is strikingly similar to the experimental one for Fm-257(s.f.). The transformation of the shape of charge distribution with increasing isospin and excitation energy occurs gradually and in a similar fashion like that of the mass distribution, but slower. For Fm-254(i.f.), Fm-257(n(th),f), and Fm-260(s.f.), the unexpected difference (symmetric or asymmetric) between the shapes of charge and mass distributions is predicted for the first time. At some critical excitation energy, the saturation of the symmetric component of charge (mass) yields is demonstrated.