Study of fission time and prescission neutron multiplicity using four-dimensional Langevin equations

2014 ◽  
Vol 23 (12) ◽  
pp. 1450087 ◽  
Author(s):  
D. Naderi
Keyword(s):  
Stochastic Dynamics ◽  
Stochastic Approach ◽  
Degree Of Freedom ◽  
Neutron Multiplicity ◽  
Langevin Equations ◽  
Orientation Degree ◽  
Four Dimensions ◽  
Dissipation Coefficient ◽  
Mass Asymmetry ◽  
Neck Thickness

In this paper, four-dimensional stochastic approach is applied on dynamics of fission process to calculate mean fission time and prescission neutron multiplicity. Elongation, neck thickness, mass asymmetry and orientation degree of freedom (K-coordinate) are four dimensions in dynamical calculations. In order to investigate the influence of the dissipation coefficient of K-coordinate, the stochastic dynamics of the orientation degree of freedom using nonconstant dissipation coefficient was studied. Calculations were done for the 16 O +208 Pb and 16 O +232 Th reactions. Obtained results were compared with a constant dissipation coefficient (γK = 0.077( MeVzs )-1/2). The mean fission time and prescission neutron multiplicity for nonconstant dissipation case were lower than for the constant one.

INFLUENCE OF NUCLEAR DISSIPATION ON PRESCISSION NEUTRON MULTIPLICITY, FISSION PROBABILITY AND FISSION TIME FOR COMPOUND NUCLEUS 210Po

2012 ◽  
Vol 21 (01) ◽  
pp. 1250008 ◽  
Author(s):  
H. ESLAMIZADEH
Keyword(s):  
Compound Nucleus ◽  
Stochastic Approach ◽  
Neutron Multiplicity ◽  
Langevin Equations ◽  
Excitation Energies ◽  
One Dimensional ◽  
Reduction Coefficient ◽  
Fission Probability ◽  
Nuclear Dissipation ◽  
Good Agreement

A stochastic approach for fission dynamics based on one-dimensional Langevin equations was applied to investigate the effect of the nuclear dissipation on the prescission neutron multiplicity, fission probability and the fission time for the compound nucleus 210 Po in an intermediate range of excitation energies 30–120 MeV. A modified wall and window dissipation with a reduction coefficient, k s , has been used in the Langevin equations. It was shown that the results of the calculations are in good agreement with the experimental data by using values of k s in the range 0.28 ≤ k s ≤ 0.50.

Mass-split dependence of pre-scission neutron multiplicity by four-dimensional Langevin dynamics in 16,18O, 40Ar and 64Ni-induced fusion–fission reactions

2019 ◽  
Vol 28 (09) ◽  
pp. 1950077
Author(s):  
D. Naderi ◽  
S. A. Alavi ◽  
V. Dehghani
Keyword(s):  
Asymmetry Parameter ◽  
Reasonable Agreement ◽  
Neutron Emission ◽  
Level Density ◽  
Neutron Multiplicity ◽  
Density Parameter ◽  
Fission Reactions ◽  
Orientation Degree ◽  
Langevin Model ◽  
Neck Thickness

By using the multidimensional Langevin model, including elongation, neck thickness, asymmetry parameter and orientation degree of freedom, the fission dynamics of some [Formula: see text]O-, [Formula: see text]Ar- and [Formula: see text]Ni-induced fusion–fission reactions were investigated. We calculated mean pre-scission neutron kinetic energy, pre-scission neutron multiplicity and fission time. Mass-split dependence of pre-scission neutron multiplicity and sensitivity of multiplicity on different value of the level density parameter for fission and neutron emission of highly excited compound nuclei were studied. One can conclude reasonable agreement between theory and tentative results for different reactions.

Effects of isospin and dissipation coefficient of the K coordinate in simulation of fission dynamics of excited compound nuclei

2020 ◽  
Vol 29 (02) ◽  
pp. 2050007
Author(s):  
H. Eslamizadeh ◽  
M. Pirpour
Keyword(s):  
Angular Distribution ◽  
Cross Section ◽  
Compound Nucleus ◽  
Stochastic Approach ◽  
Neutron Multiplicity ◽  
Dynamical Model ◽  
Fusion Reactions ◽  
Energy Distributions ◽  
Dissipation Coefficient ◽  
Fission Fragments

A stochastic approach based on four-dimensional (4D) dynamical model has been used to simulate the fission process of the excited compound nuclei [Formula: see text]Fr, [Formula: see text]Fr and [Formula: see text]Fr produced in fusion reactions. Effects of isospin and dissipation coefficient of the [Formula: see text] coordinate, [Formula: see text], on estimation of the evaporation residue (ER) cross-section, the prescission neutron multiplicity, the variance of the mass and energy distributions of fission fragments and the anisotropy of fission fragments angular distribution have been investigated for the excited compound nuclei [Formula: see text]Fr, [Formula: see text]Fr and [Formula: see text]Fr. Three collective shape coordinates [Formula: see text] plus the projection of total spin of the compound nucleus to the symmetry axis, [Formula: see text], were considered in the 4D dynamical model. In the 4D dynamical model, the magnitude of the dissipation coefficient of [Formula: see text], [Formula: see text], was considered as a free parameter and its magnitude inferred by fitting measured data on the ER cross-section. Results of the extracted dissipation coefficients of [Formula: see text] for different isotopes of Fr were shown that the magnitude of the dissipation coefficient of [Formula: see text] increases with decreasing isospin of fissioning compound nucleus. It was also shown that the prescission neutron multiplicity and the anisotropy of fission fragments angular distribution increase with increasing isospin whereas the variance of the mass and energy distributions of fission fragments decrease with increasing isospin of fissioning compound nucleus. Furthermore, it was shown that the calculated values of prescission neutron multiplicity and the variance of the mass distribution of fission fragments for the excited compound nuclei [Formula: see text]Fr, [Formula: see text]Fr and [Formula: see text]Fr decrease with the dissipation strength of [Formula: see text], whereas the variance of the energy distribution of fission fragments and the anisotropy of fission fragments angular distribution increase with the dissipation strength of [Formula: see text].

DYNAMICAL SIMULATION OF FISSION FRAGMENTS AVERAGE KINETIC ENERGY IN HEAVY-ION FUSION–FISSION REACTIONS

2011 ◽  
Vol 26 (13) ◽  
pp. 975-985 ◽  
Author(s):  
M. R. PAHLAVANI ◽  
D. NADERI ◽  
S. M. MIRFATHI
Keyword(s):  
Kinetic Energy ◽  
Three Dimensional ◽  
Heavy Ion ◽  
Langevin Equations ◽  
Average Kinetic Energy ◽  
Mass Asymmetry ◽  
Fission Fragments ◽  
Neck Thickness ◽  
Dynamical Parameters ◽  
Heavy Ion Fusion

Monte Carlo simulation based on the three-dimensional Langevin equations and one-body dissipation mechanism has been applied to highly excited compound nucleus to investigate the kinetic energy distribution of fission fragments. The effect of center to center distance between nascent fragments and other dynamical parameters (elongation, neck thickness and mass asymmetry) on average kinetic energy of fragments also studied. Finally, obtained results using this approach are compared with earlier theoretical and experimental data for a few typical systems.

Degenerate classical minima and instantons

2021 ◽  
pp. 942-959
Author(s):  
Jean Zinn-Justin
Keyword(s):  
Field Theory ◽  
Ground State ◽  
Stochastic Dynamics ◽  
Minimum Energy ◽  
Two Dimensions ◽  
Quantum Theories ◽  
Four Dimensions ◽  
Quantum Tunnelling ◽  
Charge Conjugation Parity ◽  
Double Well Potential

Instantons play an important role in the following situation: quantum theories corresponding to classical actions that have non-continuously connected degenerate minima. The simplest examples are provided by one-dimensional quantum systems with symmetries and potentials with non-symmetric minima. Classically, the states of minimum energy correspond to a particle sitting at any of the minima of the potential. The position of the particle breaks (spontaneously) the symmetry of the system. By contrast, in quantum mechanics (QM), the modulus of the ground-state wave function is large near all the minima of the potential, as a consequence of barrier penetration effects. Two typical examples illustrate this phenomenon: the double-well potential, and the cosine potential, whose periodic structure is closer to field theory examples. In the context of stochastic dynamics, instantons are related to Arrhenius law. The proof of the existence of instantons relies on an inequality related to supersymmetric structures, and which generalizes to some field theory examples. Again, the presence of instantons again indicates that the classical minima are connected by quantum tunnelling, and that the symmetry between them is not spontaneously broken. Examples of such a situation are provided, in two dimensions, by the charge conjugation parity (CP) (N − 1) models and, in four dimensions, by SU(2) gauge theories.

scholarly journals Neutron excess dependence of fusion barrier parameters

2019 ◽  
Vol 11 ◽  
Author(s):  
N. G. Nicolis
Keyword(s):  
Barrier Height ◽  
Potential Application ◽  
Heavy Ion ◽  
Degree Of Freedom ◽  
Entrance Channel ◽  
Neutron Excess ◽  
Fusion Barrier ◽  
Mass Asymmetry ◽  
Heavy Ion Fusion

The neutron excess dependence of heavy ion fusion barrier parameters is investigated, guided by predictions of different heavy ion potentials. We develop parametrizations for the fusion barrier height and radius which explicitly involve the entrance channel mass asymmetry and neutron excess of the projectile and target. The developed expressions reproduce theoretical barrier parameters within 0.2%, which represents a big improvement over previous parametrizations. Furthermore, they provide a means to assess the importance of the neutron excess degree of freedom implied by each potential. Application of these expressions to systematics of experimental barrier parameters will be discussed.

Effect of the orientation degree of freedom on the rate and time of fission of highly excited nuclei

2011 ◽  
Vol 74 (3) ◽  
pp. 341-351 ◽  
Author(s):  
Yu. A. Anischenko ◽  
A. E. Gegechkori ◽  
G. D. Adeev
Keyword(s):  
Degree Of Freedom ◽  
Orientation Degree ◽  
Excited Nuclei
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