Large-amplitude Dynamical Motion and Fluctuations in Nuclear Fission and Heavy-ion Reactions
Large-amplitude Dynamical Motion and Fluctuations in Nuclear Fission and Heavy-ion Reactions

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Published: 1981

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In studies of the dynamics of large-amplitude nuclear motion, a useful starting point is the separation of the total degrees of freedom into two types: a few collective degrees of freedom describing the shape of the nuclear surface that are treated explicitly and the remaining relatively large number of internal degrees of freedom that are treated implicitly. Once such a separation has been made, it is necessary to describe the transfer of energy between the collective and internal degrees of freedom, as well as the Brownian fluctuations in the collective degrees of freedom arisng from an implicit treatment of the internal degrees of freedom. The goal of the present work is, unlike previous efforts, to describe simultaneously both the average dynamical motion and the Brownian fluctuations in terms of quantities that are calculated from specified nuclear models. The general approach is described, but no results have been obtained as yet. (RWR).

Dynamical Calculations of Nuclear Fission and Heavy-ion Reactions
Dynamical Calculations of Nuclear Fission and Heavy-ion Reactions

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Published: 1984

Total Pages:

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With the goal of determining the magnitude and mechanism of nuclear dissipation from comparisons of predictions with experimental data, we describe recent calculations in a unified macroscopic-microscopic approach to large-amplitude collective nuclear motion such as occurs in fission and heavy-ion reactions. We describe the time dependence of the distribution function in phase space of collective coordinates and momenta by a generalized Fokker-Planck equation. The nuclear potential energy of deformation is calculated as the sum of repulsive Coulomb and centrifugal energies and an attractive Yukawa-plus-exponential potential, the inertia tensor is calculated for a superposition of rigid-body rotation and incompressible, nearly irrotational flow by use of the Werner-Wheeler method, and the dissipation ensor that describes the conversion of collective energy into single-particle excitation energy is calculated for two prototype mechanisms that represent opposite extremes of large and small dissipation. We solve the generalized Hamilton equations of motion for the first moments of the distribution function to obtain the mean translational fission-fragment kinetic energy and mass of a third fragment that sometimes forms between the two end fragments, as well as dynamical thresholds, capture cross sections, and ternary events in heavy-ion reactions. 33 references.

Dynamics of Nuclear Fission and Heavy-ion Reactions
Dynamics of Nuclear Fission and Heavy-ion Reactions

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Published: 1979

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Large-amplitude collective motion in fission and heavy-ion reactions is studied by solving classical equations of motion for the time evolution of the nuclear shape. In the nuclear potential energy of deformation, the generalized surface energy was calculated by means of a double volume integral of a Yukawa-plus-exponential function, which was obtained by requiring that two semi-infinite slabs of constant-density nuclear matter have minimum energy at zero separation. The collective kinetic energy is calculated for nuclear flow that is a superposition of incompressible, nearly irrotational collective-shape motion and rigid-body rotation. Nuclear dissipation is included by means of the Rayleigh dissipation function, which depends upon the physical mechanism that converts collective energy into internal energy. For both ordinary two-body viscosity and a combined wall and window one-body dissipation, fission-fragment kinetic energies are calculated for the fission of nuclei throughout the periodic table and compare with experimental results. Finally, the one-body dynamics of nucleons inside a cylinder colliding with a moving piston is explicitly studied by solving exactly the collisionless Boltzmann equation for the distribution function. By examining the relative phases of the pressure at the piston and the piston's velocity, a dissipative force and an elastic restoring force can be separately identified. 9 references.

Dynamics of Fission and Heavy Ion Reactions
Dynamics of Fission and Heavy Ion Reactions

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Published: 1984

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Recent advances in a unified macroscopic-microscopic description of large-amplitude collective nuclear motion such as occurs in fission and heavy ion reactions are discussed. With the goal of finding observable quantities that depend upon the magnitude and mechanism of nuclear dissipation, one-body dissipation and two-body viscosity within the framework of a generalized Fokker-Planck equation for the time dependence of the distribution function in phase space of collective coordinates and momenta are considered. Proceeding in two separate directions, the generalized Hamilton equations of motion for the first moments of the distribution function with a new shape parametrization and other technical innovations are first solved. This yields the mean translational fission-fragment kinetic energy and mass of a third fragment that sometimes forms between the two end fragments, as well as the energy required for fusion in symmetric heavy-ion reactions and the mass transfer and capture cross section in asymmetric heavy-ion reactions. In a second direction, we specialize to an inverted-oscillator fission barrier and use Kramers' stationary solution to calculate the mean time from the saddle point to scission for a heavy-ion-induced fission reaction for which experimental information is becoming available. 25 references.

Large-scale Collective Motion Of Atomic Nuclei - Proceedings Of The International Symposium
Large-scale Collective Motion Of Atomic Nuclei - Proceedings Of The International Symposium

Author: Giorgio Giardina

Publisher: World Scientific

Published: 1997-07-01

Total Pages: 762

ISBN-13: 9814546461

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The scope of the international meeting covered a broad range of the recent developments in nuclear physics, from heavy-ion collisions from Coulomb barrier through relativisitc energies (using stable and radioactive beams), to some applications of nuclear physics and other research fields. The lectures given at the meeting range from the most recent progress to future prospects in nuclear physics research.This volume focuses on recent developments in nuclear physics, with emphasis on the investigation of processes connected with large-amplitude collective motion in nuclei, such as heavy-ion fusion, giant multipole resonances, and nuclear fission and fragmentation.

Energy Research Abstracts
Energy Research Abstracts

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Published: 1994

Total Pages: 1032

ISBN-13:

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Semiannual, with semiannual and annual indexes. References to all scientific and technical literature coming from DOE, its laboratories, energy centers, and contractors. Includes all works deriving from DOE, other related government-sponsored information, and foreign nonnuclear information. Arranged under 39 categories, e.g., Biomedical sciences, basic studies; Biomedical sciences, applied studies; Health and safety; and Fusion energy. Entry gives bibliographical information and abstract. Corporate, author, subject, report number indexes.

Theoretical Approaches of Heavy Ion Reaction Mechanisms
Theoretical Approaches of Heavy Ion Reaction Mechanisms

Author: M. Martinot

Publisher: Elsevier

Published: 2016-06-03

Total Pages: 443

ISBN-13: 148325710X

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Theoretical Approaches of Heavy Ion Reaction Mechanisms provides information pertinent to heavy ion reactions and nuclear fission at low energies. This book discusses the features of the time-dependent solution of the Kramer–Chandrasekhar equation. Organized into 27 chapters, this book begins with an overview of the deexcitation process of a highly excited nucleus by means of its decay into two fragments. This text then presents a microscopic description to extract the characteristics features of the collective dynamics of the fission process at low energy. Other chapters consider nuclear fission as a transport process over the fission barrier. This book discusses as well the microscopic foundations of the phenomenological collective models. The final chapter deals with the composition of the baryons and mesons in terms of gluons and quarks. This book is a valuable resource for nuclear and high energy physicists. Experimentalists, theoreticians, and research workers will also find this book useful.

Stochastic Approaches to Dynamics of Heavy Ion Collisions, the Case of Thermal Fission
Stochastic Approaches to Dynamics of Heavy Ion Collisions, the Case of Thermal Fission

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Publisher:

Published: 1994

Total Pages: 12

ISBN-13:

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In order to study the influence of fluctuations on various phenomena linked to heavy ion collisions, a Langevin equation has been derived from a microscopic model. Parameters entering this equation are completely determined from microscopic quantities characterizing nuclear matter. This equation has been applied to various phenomena at intermediate energies. This paper focuses on large amplitude motions and especially thermal fission. Fission rate is calculated and compared to experimental results.