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Title: Competition between fusion and quasifission in a heavy fusing system: Diffusion of nuclear shapes through a dynamical collective potential energy landscape

Abstract

A theory of the competition between fusion and quasifission in a heavy fusing system is proposed, which is based on a master equation and the two-center shell model. Fusion and quasifission arise from a diffusion process in an ensemble of nuclear shapes, each of which evolves toward the thermal equilibrium. The fusing system moves on a dynamical (time-dependent) collective potential energy surface that is initially diabatic and gradually becomes adiabatic. Calculations for several reactions leading to {sup 256}No are performed within a simplified two-dimensional model. Among other important conclusions, the results indicate that (i) the diabatic effects play a very important role in the onset of fusion hindrance for heavy systems and (ii) very asymmetric reactions induced by closed-shell nuclei seem to be the best suited to synthesize the heaviest compound nuclei.

Authors:
 [1]
  1. Department of Nuclear Physics, Research School of Physical Sciences and Engineering, Australian National University, Canberra, ACT 0200 (Australia) and Institut fuer Theoretische Physik der Johann Wolfgang Goethe-Universitaet Frankfurt, Max von Laue Str. 1, D-60438 Frankfurt (Germany)
Publication Date:
OSTI Identifier:
20864206
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. C, Nuclear Physics; Journal Volume: 74; Journal Issue: 6; Other Information: DOI: 10.1103/PhysRevC.74.064601; (c) 2006 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; ASYMMETRY; COMPOUND NUCLEI; DIFFUSION; HEAVY ION FUSION REACTIONS; NOBELIUM 256; POTENTIAL ENERGY; QUASI-FISSION; SHELL MODELS; THERMAL EQUILIBRIUM; TIME DEPENDENCE; TWO-DIMENSIONAL CALCULATIONS

Citation Formats

Diaz-Torres, Alexis. Competition between fusion and quasifission in a heavy fusing system: Diffusion of nuclear shapes through a dynamical collective potential energy landscape. United States: N. p., 2006. Web. doi:10.1103/PHYSREVC.74.064601.
Diaz-Torres, Alexis. Competition between fusion and quasifission in a heavy fusing system: Diffusion of nuclear shapes through a dynamical collective potential energy landscape. United States. doi:10.1103/PHYSREVC.74.064601.
Diaz-Torres, Alexis. Fri . "Competition between fusion and quasifission in a heavy fusing system: Diffusion of nuclear shapes through a dynamical collective potential energy landscape". United States. doi:10.1103/PHYSREVC.74.064601.
@article{osti_20864206,
title = {Competition between fusion and quasifission in a heavy fusing system: Diffusion of nuclear shapes through a dynamical collective potential energy landscape},
author = {Diaz-Torres, Alexis},
abstractNote = {A theory of the competition between fusion and quasifission in a heavy fusing system is proposed, which is based on a master equation and the two-center shell model. Fusion and quasifission arise from a diffusion process in an ensemble of nuclear shapes, each of which evolves toward the thermal equilibrium. The fusing system moves on a dynamical (time-dependent) collective potential energy surface that is initially diabatic and gradually becomes adiabatic. Calculations for several reactions leading to {sup 256}No are performed within a simplified two-dimensional model. Among other important conclusions, the results indicate that (i) the diabatic effects play a very important role in the onset of fusion hindrance for heavy systems and (ii) very asymmetric reactions induced by closed-shell nuclei seem to be the best suited to synthesize the heaviest compound nuclei.},
doi = {10.1103/PHYSREVC.74.064601},
journal = {Physical Review. C, Nuclear Physics},
number = 6,
volume = 74,
place = {United States},
year = {Fri Dec 15 00:00:00 EST 2006},
month = {Fri Dec 15 00:00:00 EST 2006}
}
  • A realistic microscopically-based quantum approach to the competition between fusion and quasi-fission in a heavy fusing system is applied to several reactions leading to 256No. Fusion and quasi-fission are described in terms of a diffusion process of nuclear shapes through a dynamical collective potential energy landscape which is initially diabatic and gradually becomes adiabatic. The microscopic ingredients of the theory are obtained with a realistic two-center shell model based on Woods-Saxon potentials. The results indicate that (i) the diabatic effects play a very important role in the onset of fusion hindrance for heavy systems, and (ii) very asymmetric reactions inducedmore » by closed shell nuclei seem to be the best suited to synthesize the heaviest compound nuclei.« less
  • A model based on the dinuclear system concept is suggested for the calculation of the competition between complete fusion and quasifission in reactions with heavy nuclei. The fusion rate through the inner fusion barrier in mass asymmetry is found by using the Kramers-type expression. The calculated cross sections for the heaviest nuclei are in a good agreement with the experimental data. The experimentally observed rapid fall-off of the cross section of the cold fusion with increasing charge number Z of the compound nucleus is explained.
  • Cited by 20
  • The angular distributions of fission fragments for the {sup 32}S+{sup 184}W reaction at center-of-mass energies of 118.8, 123.1, 127.3, 131.5, 135.8, 141.1, and 144.4 MeV are measured. The experimental fission excitation function is obtained. The anisotropy (A{sub exp}) is found by extrapolating each fission fragment angular distribution. The measured fission cross sections of the {sup 32}S+{sup 182,184}W reaction are decomposed into fusion-fission, quasifission, and fast-fission contributions by the dinuclear system model (DNS). The angular momentum distributions of the dinuclear system and compound nucleus calculated by the DNS model are used to reproduce the experimental capture and fusion excitation functions formore » both reactions and quantities K{sub 0}{sup 2}, <l{sup 2}>, and A{sub exp}, which characterize angular distributions of the fission products at the considered range of beam energy. The total evaporation residue excitation function for the {sup 32}S+{sup 184}W reaction calculated in the framework of the advanced statistical model is close to the available experimental data only up to about E{sub c.m.}approx =160 MeV. The underestimation of the experimental data at high excitation energies E{sub c.m.}>160 MeV is explained by the fact that the statistical model cannot reproduce the cross section of evaporation residues formed by the nonequilibrium mechanism, that is, without formation of the compound nucleus in the statistical equilibrium state.« less