Abstract
Fragment mass distributions for fission after full momentum transfer were measured in the reactions of 30 Si,34,36 S,31 P,40 Ar + 238 U at bombarding energies around the Coulomb barrier. Mass distributions change significantly as a function of incident beam energy. The asymmetric fission probability increases at sub-barrier energy. The phenomenon is interpreted as an enhanced quasifission probability owing to orientation effects on fusion and/or quasifission. The evaporation residue (ER) cross sections were measured in the reactions of 30 Si + 238 U and 34 S + 238 U to obtain information on fusion. In the latter reaction, significant suppression of fusion was implied. This suggests that fission events different from compound nucleus are included in the masssymmetric fragments. The results are supported by a model calculation based on a dynamical calculation using Langevin equation, in which the mass distribution for fusion-fission and quasifission fragments are separately determined.
Highlights
Experiments to produce superheavy nuclei (SHN) have been carried out by using heavy ion fusion reactions [1,2,3]
The reaction is considered to proceed in three steps; (1) penetration of the Coulomb barrier between two colliding nuclei, (2) formation of a compound nucleus after the system is captured inside the Coulomb barrier and (3) survival of the excited compound nucleus to produce evaporation residue (ER) against fission
The mass distributions and cross sections of fission fragments in the reactions of 30Si,34,36S,31P,40Ar + 238U were measured using beams supplied by the tandem accelerator of the Japan Atomic Energy Agency (JAEA) in Tokai, Japan
Summary
Experiments to produce superheavy nuclei (SHN) have been carried out by using heavy ion fusion reactions [1,2,3]. Development of a theoretical model to predict cross sections for nuclei located at the extreme end of heavy elements is important for the proper selection of target and projectile as well as the bombarding energy to produce these nuclei. Fusion reactions using actinide target nuclei are extensively used to investigate SHN [1]. The accurate prediction of the cross sections for actinide-based reactions is important to explore this field. Have investigated the effects of nuclear orientation on fusion and/or quasifission by measuring the fission fragment mass distributions in the reactions using 238U target nucleus. We measured the ER cross sections as a direct evidence for fusion to confirm the validity of the fusion probability obtained from fission measurement
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