Nuclear fission with diffusive dynamics

Cha, Dongwoo; Bertsch, G. F.

doi:10.1103/physrevc.46.306

Cited by 14 publications

(4 citation statements)

References 17 publications

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“…It is, there-fore, extremely interesting to derive the one-body friction or its equivalent by microscopic theories. Recent microscopic calculations of diffusion coefficient [16] and friction constant [17], however, appear to give too strong dissipation for nuclear collective motions. Yamaji et al [18], on the other hand, obtained a friction coefficient comparable with the wall formula using the linear response theory.…”

Section: \/N(t)][dn(t)/dt]mentioning

confidence: 99%

One-body dissipation in agreement with prescission neutrons and fragment kinetic energies

1993

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Fission dynamics of hot nuclei have been investigated using the two-dimensional Langevin equation. Including particle evaporation in the continuous limit, prescission multiplicities of neutrons, protons, and a particles have been calculated. Both the calculated number of prescission neutrons and the average total kinetic energy of fission fragments are consistent with experimental values when one-body dissipation is assumed. Unusually strong hydrodynamical two-body viscosity also reproduces the experimental neutron multiplicity, but it significantly underestimates the average kinetic energy. PACS numbers: 25.70.Jj, 25.85.Ge Collective motions of highly excited nuclei have been one of the interesting topics in nuclear physics in the last several years. Fissioning motion is a typical one and provides a good field to study nuclear collective dynamics in high excitation, i.e., fluctuation, dissipation, etc. One viewpoint is to consider collective degrees of freedom as Brownian particles and nucleonic ones as the heat bath. Thus, a primary interest is how strong friction is exerted on collective motions. Experimental evidence of fission as a slow and highly dissipative process has come from prescission multiplicities of neutrons [1], charged particles [2], and / rays [3]. In particular, neutrons are expected to work as a clock to measure fission time scale, because of their short life. Hinde, Hilscher, and Rossner [1] observed a prescission neutron multiplicity much larger than the value obtained with a simple statistical model. To analyze the prescission neutron data, they had to introduce a long delay time (~5xlO -20 s) during which fission cannot occur. From the observation of prescission 7 rays, Thoennessen et al. [3] also found a hindrance of fission consistent with neutron data. The delay time has been interpreted as a transient time during which the fissioning degree of freedom attains ''thermal equilibrium" inside the potential pocket, more precisely, quasistationary distribution in the phase space [4]. It depends on the strength of the friction force which is interpreted as the average effect of the interaction of the slow collective motion with already thermalized nucleons. Therefore, the friction constant of nuclear matter can be deduced by analyzing the fission time scale using the Fokker-Planck or Langevin equation.The kinetic energy distribution of fission fragments is another important observable related to fission dynamics; it is related to the descent from saddle to scission. Recently, realistic calculations were made for these two physical quantities using the two-dimensional Langevin equation with both one-body friction and hydrodynamical two-body viscosity [5]. The transient time obtained using the usual hydrodynamical viscosity [6] was 10 times shorter than that extracted from experiment. A stronger viscosity leads to a longer transient time but to a too small average kinetic energy of fission fragments when compared with Viola systematics [7]. On the other hand, the one-body friction gave an ...

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Section: \/N(t)][dn(t)/dt]mentioning

confidence: 99%

One-body dissipation in agreement with prescission neutrons and fragment kinetic energies

1993

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“…Theoretically, many authors derived that the transient time is needed for slow fission mode to attain its stationary decay rate [7][8][9][10][11][12][13][14][15][16][17][18]. In general case, Langevin equation and FokkerPlanck equation is solved analytically with difficulities.…”

Section: Introductionmentioning

confidence: 99%

Angular momentum effect in prescission particle multiplicities for a light system by diffusion model

Shen

et al. 1997

Z Phys A - Particles and Fields

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The effect of angular momentum on the competition between fission and particle emission during light system fission process was studied via fission diffusion model. The prescission particle multiplicities were found to increase with decreasing angular momentum. The experimental prescission proton and α particle multiplicities can be fitted for 10.6 MeV/nucleon 84 Kr( 27 Al,binary fission) reaction with this model. Entrance channel effect found in [1] is proved to be angular momentum effect.

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“…Recent publications, however, claim the failure of the transition state rates to account for the measured amounts of prescission neutrons or γ-rays in relatively heavy fissioning systems [11,12,13] . This alleged failure has been attributed to the transient time necessary for the so-called slow fission mode to attain its stationary decay rate [14,15,16,17,18,19,20,21] . The experimental methods of these studies suffer from two difficulties: First they require a possibly large correction for post-saddle, but pre-scission emission; second, they are indirect methods since they do not directly determine the fission probability.…”

Section: Introductionmentioning

confidence: 99%

Scaling Laws, Transient Times and Shell Effects in Helium Induced Nuclear Fission

Rubehn

Jing

Moretto

et al. 1996

Advances in Nuclear Dynamics 2

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Fission excitation functions of compound nuclei in a mass region where shell effects are expected to be very strong are shown to scale exactly according to the transition state prediction once these shell effects are accounted for. The fact that no deviations from the transition state method have been observed within the experimentally investigated exci-tation energy regime allows one to assign an upper limit for the transient time of 10 −20 seconds. PACS number(s): 25.85.Ge, 24.75.+i

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Nuclear fission with diffusive dynamics

Cited by 14 publications

References 17 publications

One-body dissipation in agreement with prescission neutrons and fragment kinetic energies

One-body dissipation in agreement with prescission neutrons and fragment kinetic energies

Angular momentum effect in prescission particle multiplicities for a light system by diffusion model

Scaling Laws, Transient Times and Shell Effects in Helium Induced Nuclear Fission

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