Investigating fusion dynamics at high angular momentum via fission cross sections

Department of Nuclear Physics, Research School of Physical Sciences and Engineering, The Australian National University, Canberra, ACT 2601, Australia

^* e-mail: asckj1@yahoo.co.in; Present Address: Department of Nuclear and Atomic Physics, Tata Institute of Fundamental Research, Mumbai-400 005, India
^** e-mail: David.Hinde@anu.edu.au

Published online: 22 November 2017

Abstract

A quantitative understanding of fusion dynamics at high angular momentum is attempted employing experimental fission cross sections as a probe and carrying out a simultaneous description of the fusion and fission cross sections at above barrier energies. For this, experimental fission fragment angular distributions for three systems: ¹⁶O+¹⁴⁸Sm, ²⁸Si+¹³⁶Ba and ⁴⁰Ca+¹²⁴Sn, all forming the same compound nucleus ¹⁶⁴Yb at similar excitation energies, have been measured at four beam energies above their respective capture barriers. A simultaneous description of the angle integrated fission cross sections and evaporation residue/fusion cross sections available in literature for the systems is carried out using coupled-channels and statistical model calculations. Fission cross sections, which are most sensitive to the changes in angular momentum, provide very stringent constraints for model calculations thus indicating the need of precision evaporation residue as well as fission cross sections in such studies. A large diffuseness (a_o>0.65 fm) of the nuclear potential gives the best reproduction of the experimental data. In addition, different coupling schemes give very different angular momentum distributions, which, in turn, give very different fission cross section predictions. Both these observations hint at the explanation that depending on energy dissipation of the interacting nuclei occurring inside or outside the fusion pocket, very different fission cross sections can result due to heavily altered angular momentum and thus justifies the sensitivity of fission cross sections used as probes in the present work.