Flerov Laboratory of Nuclear Reactions

Seminar of Physical Sectors

Date and Time: Tuesday, 1 October 2019, at 3:30 PM

Venue: Conference Hall, Flerov Laboratory of Nuclear Reactions

Seminar topic: «Exploring fusion and quasifission in reactions populating heavy and medium heavy nuclei»

Speaker: E. Prasad (Central University of Kerala, India)

Abstract:

Heavy-ion fusion – the only established method that opens the doors to the world of superheavy elements – is a complex process that involves a large scale collective rearrangement of nuclear matter. The existence of super heavy elements (SHEs) beyond the macroscopic limit of the liquid drop model is believed to be due to the microscopic stabilization arising from shell structure. The heavy evaporation residues formation in heavy-ion fusion is often treated as a three-step process – the capture, the CN formation and the survival of the formed CN against fission. Unlike in lighter, mass asymmetric reactions, capture does not guarantee the formation of the CN in heavy, mass-symmetric systems. There is strong competition from quasifission in the entrance channel, which severely inhibits fusion. Being a dynamical process, and having a strong dependence on various quantities, an exact nature of quasifission is not fully known. Complete understanding of fusion and quasifission processes are essential to make reliable predictions for the best projectile-target combinations that would produce new heavy and super heavy nuclei.
To understand the mechanism of fusion and quasifission, a series of measurements were performed using the Indian and Australian facilities, forming nuclei in the ~ 175- 270 mass region. Fission fragment mass distribution and fission cross sections were measured for a number of reactions populating very heavy nuclei at ANU, Canberra. Fusion evaporation residue cross-sections of reactions forming medium-heavy compound systems were measured at the Indian facilities. Neutron multiplicities were measured for a number of reactions using the National Array of Neutron detectors. Attempts were also made to understand the mechanism of fission in sub-lead systems at very low excitation energies. Important experimental findings and results will be discussed in the talk.