Nuclear orientation in the reaction S34+U238 and synthesis of the new isotope Hs268

The synthesis of isotopes of the element hassium was studied using the reaction S34+U238→Hs272^*. At a kinetic energy of 163.0MeV in the center-of-mass system we observed one α-decay chain starting at the isotope Hs267. The cross section was 1.8-1.5+4.2 pb. At 152.0MeV one decay of the new isotope Hs268 was observed. It decays with a half-life of 0.38-0.17+1.8 s by 9479±16keV α-particle emission. Spontaneous fission of the daughter nucleus Sg264 was confirmed. The measured cross section was 0.54-0.45+1.3 pb. In-beam measurements of fission-fragment mass distributions were performed to obtain information on the fusion probability at various orientations of the deformed target nucleus. The distributions changed from symmetry to asymmetry when the beam energy was changed from above-barrier to sub-barrier values, indicating orientation effects on fusion and/or quasifission. It was found that the distribution of symmetric mass fragments originates not only from fusion-fission, but has a strong component from quasifission. The result was supported by a calculation based on a dynamical description using the Langevin equation, in which the mass distributions for fusion-fission and quasifission fragments were separately determined.