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Title: Quantum diffusion approach to the formation of a heavy compound nucleus by heavy-ion fusion reactions

Abstract

We discuss quantum effects in the diffusion process which is used to describe the shape evolution from the touching configuration of fusing two nuclei to a compound nucleus. Applying the theory with quantum effects to the case where the potential field, the mass and the friction parameters are adapted to realistic values of heavy-ion collisions, we show that the quantum effects play significant roles at low temperatures which are relevant to the synthesis of superheavy elements. We also discuss the mass distribution of the quasi-fission fragments calculated in the two-dimensional quantum Langevin approach.

Authors:
;  [1];  [2]
  1. Department of Physics, Tohoku University, 980-8578 Sendai (Japan)
  2. Physics Department, Tennessee Technological University, Cookeville, Tennessee 38505 (United States)
Publication Date:
OSTI Identifier:
21056771
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 891; Journal Issue: 1; Conference: 6. Symposium on nuclear physics, Tours (France), 5-8 Sep 2006; Other Information: DOI: 10.1063/1.2713546; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; COMPOUND NUCLEI; DIFFUSION; FISSION FRAGMENTS; FRICTION; HEAVY ION FUSION REACTIONS; HEAVY NUCLEI; MASS DISTRIBUTION; NUCLEAR TEMPERATURE; POTENTIALS; QUASI-FISSION; TRANSACTINIDE ELEMENTS; TWO-DIMENSIONAL CALCULATIONS

Citation Formats

Washiyama, Kouhei, Takigawa, Noboru, and Ayik, Sakir. Quantum diffusion approach to the formation of a heavy compound nucleus by heavy-ion fusion reactions. United States: N. p., 2007. Web. doi:10.1063/1.2713546.
Washiyama, Kouhei, Takigawa, Noboru, & Ayik, Sakir. Quantum diffusion approach to the formation of a heavy compound nucleus by heavy-ion fusion reactions. United States. doi:10.1063/1.2713546.
Washiyama, Kouhei, Takigawa, Noboru, and Ayik, Sakir. Mon . "Quantum diffusion approach to the formation of a heavy compound nucleus by heavy-ion fusion reactions". United States. doi:10.1063/1.2713546.
@article{osti_21056771,
title = {Quantum diffusion approach to the formation of a heavy compound nucleus by heavy-ion fusion reactions},
author = {Washiyama, Kouhei and Takigawa, Noboru and Ayik, Sakir},
abstractNote = {We discuss quantum effects in the diffusion process which is used to describe the shape evolution from the touching configuration of fusing two nuclei to a compound nucleus. Applying the theory with quantum effects to the case where the potential field, the mass and the friction parameters are adapted to realistic values of heavy-ion collisions, we show that the quantum effects play significant roles at low temperatures which are relevant to the synthesis of superheavy elements. We also discuss the mass distribution of the quasi-fission fragments calculated in the two-dimensional quantum Langevin approach.},
doi = {10.1063/1.2713546},
journal = {AIP Conference Proceedings},
number = 1,
volume = 891,
place = {United States},
year = {Mon Feb 26 00:00:00 EST 2007},
month = {Mon Feb 26 00:00:00 EST 2007}
}
  • We discuss quantum effects in the diffusion process which is used to describe the shape evolution from the touching configuration of fusing two nuclei to a compound nucleus. Applying the theory with quantum effects to the case where the potential field, the mass and friction parameters are adapted to realistic values of heavy-ion collisions, we show that the quantum effects play significant roles at low temperatures which are relevant to the synthesis of superheavy elements.
  • The alpha-particle spectra and the proton spectra at different laboratory angles from the fusion reactions {sup 16}O+{sup 64}Zn at 95 Mev and {sup 32}S+{sup 48}Ti at 125 MeV were measured. Both systems have zero channel spin and lead to the compound nucleus {sup 80}Sr{sup *} with the same value of l{sub max}=43({Dirac_h}/2{pi}). The observed spectra from the asymmetric reaction {sup 16}O+{sup 64}Zn reaction can be reproduced with the statistical model calculations using rotating liquid drop model values of moment of inertia and transmission coefficients for spherical nuclei. However, the charged particle spectra in case of the symmetric {sup 32}S+{sup 48}Timore » reaction are not in agreement with the predictions of the statistical model. In order to explain the experimental spectra for the {sup 32}S+{sup 48}Ti reaction, the analysis was done using the dynamical model of Feldmeier et al. [Rep. Prog. Phys. 50, 915 (1987)]. This analysis shows that the effective l{sub max} value for fusion to take place in the case of the symmetric system is lowered to 30({Dirac_h}/2{pi}). The statistical model calculations for the dynamical model predicted the l{sub max} value reproduced the observed spectra reasonably well indicating entrance channel effects on the decay of the compound nucleus.« less
  • We study the effect of the nuclear macroscopic energy, nuclear dissipation, and shape parametrization on dynamical thresholds for compound-nucleus formation in symmetric heavy-ion reactions. This is done by solving numerically classical equations of motion for head-on collisions to determine whether the dynamical trajectory in a multidimensional deformation space passes inside the fission saddle point and forms a compound nucleus, or whether it passes outside the fission saddle point and reseparates. Specifying the nuclear shape in terms of smoothly joined portions of three quadratic surfaces of revolution, we take into account three symmetric deformation coordinates. However, in some cases we reducemore » the number of coordinates to two by requiring the ends of the fusing system to be spherical in shape. The nuclear potential energy of deformation is determined in terms of a Coulomb energy and a nuclear macroscopic energy that is usually taken to be a double volume energy of a Yukawa-plus-exponential folding function, although a double volume integral of a single-Yukawa folding function and ordinary surface energy are also considered. The collective kinetic energy is calculated for incompressible, nearly irrotational flow by means of the Werner-Wheeler approximation. Four possibilities are studied for the transfer of collective kinetic energy into internal single-particle excitation energy: (1) zero dissipation, (2) ordinary two-body viscosity, (3) one-body wall-formula dissipation, and (4) one-body wall-and-window dissipation. For systems with Z/sup 2//A larger than a threshold value (Z/sup 2//A)/sub thr/ which depends somewhat upon dissipation, the center-of-mass bombarding energy must exceed the maximum in the one-dimensional interaction barrier by an amount ..delta..E in order to form a compound nucleus.« less
  • The entrance-channel mass-asymmetry dependence of the compound nucleus formation time in light heavy-ion reactions has been investigated within the framework of semiclassical dissipative collision models. The model calculations have been applied successfully to the formation of the {sup 38}Ar compound nucleus as populated via the {sup 9}Be+{sup 29}Si, {sup 11}B+{sup 27}Al, {sup 12}C+{sup 26}Mg, and {sup 19}F+{sup 19}F entrance channels. The shape evolution of several other light composite systems appears to be consistent with the so-called {open_quote}{open_quote}Fusion Inhibition Factor{close_quote}{close_quote} which has been observed experimentally. As found previously in more massive systems for the fusion-evaporation process, the entrance-channel mass-asymmetry degree ofmore » freedom appears to determine the competition between the different mechanisms as well as the time scales involved. {copyright} {ital 1996 The American Physical Society.}« less
  • The compound-nucleus formation cross sections were calculated for a number of reactions. The information about the parameters of nuclear interaction between nuclei, which was obtained fromn the quasi-classical analysis of experiments on heavy ion elastic scattering, was used. It was established that the account of such an interaction is important. (auth)