Nuclear orientation in the reactionS34+U238and synthesis of the new isotopeHs268

Abstract

The synthesis of isotopes of the element hassium was studied using the reaction S34+U238→Hs272*. At a kinetic energy of 163.0 MeV 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 152.0 MeV 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±16 keV 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.Received 2 July 2010DOI:https://doi.org/10.1103/PhysRevC.82.024611©2010 American Physical Society