Modification of microstructures induced by temperature variation during irradiation with 14 MeV neutrons
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The deformation properties of heavy nuclei undergoing the individual fission paths are studied. To understand the nuclear mass division process at low energy, fission events for the symmetric and asymmetric fission paths are analyzed from the overall fission events. The fragment mass-yield distributions for the symmetric and asymmetric fission paths in the fission processes of 210Po, 227Ac, 233Pa, 249Bk, and 259Md are systematically studied. Fission characteristics including the deformation of the fissioning nucleus at the scission configuration, the fragment massyield distributions, and the total kinetic energy release for individual fission paths are presented.
Nuclear fission
Cold fission
Spontaneous fission
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A reanalysis of selected fission fragment angular distributions is made using formulae derived in the previous paper. In contrast to previous results it is concluded that the recent heavy-ion-induced fission data is consistent with standard assumptions of fission, although it is suggested that incomplete fusion plays a major role in high energy heavy ion collisions leading to fission.
Fragment (logic)
Cold fission
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Cold fission
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Fragment (logic)
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Bond cleavage
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Cold fission
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P92 steel was irradiated with Ar ion up to 10 dpa at 200, 400, and 700 °C. The effect of Ar ion irradiation on hardness was investigated with nanoindentation tests and microstructure analyses. It was observed that irradiation-induced hardening occurred in the steel after Ar ion irradiation at all three temperatures to 10 dpa. The steel exhibited significant hardening at 200 and 700 °C, and slight hardening at 400 °C under Ar ion irradiation. Difference in the magnitude of irradiation-induced hardening at different temperature in the steel is attributed to different changes in the microstructure of the steel that arose from the irradiation. Irradiation-induced hardening in the P92 steel irradiated at 200 °C is attributed to the occurrence of both dislocation loops and other fine irradiation defects during irradiation. Slight hardening in the steel irradiated at 400 °C mainly arises from the annihilation of defect clusters at this temperature. The occurrence of fine Ar bubbles with high number density during the Ar ion irradiation at 700 °C resulted in the significant hardening in the steel.
Hardening (computing)
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Nuclear fission
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The model for fission fragment mass distributions and results of calculations for low energy fission and fission induced by intermediate energy nucleons is presented. Formation of mass distributions is considered as a result of oscillations on mass asymmetry degree of freedom in the potential well calculated in the macroscopic‐microscopic approach. For intermediate energy fission the distribution of fissioning nuclei is taken into account with detailed reaction calculations including direct, preequilibrium and statistical reaction stages.
Mass distribution
Fragment (logic)
Nuclear fission
Cold fission
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Fission transients describe the fission rate as it evolves towards the quasistationary value given by Kramers' formula. The nature of fission transients is dependent on the assumed initial distribution of the compound nuclei along the fission coordinate. Although the standard initial assumption of a near-spherical object leads to a transient suppression of the fission rate (fission delay), a moderate initial fissionlike deformation can reduce the magnitude of this suppression. For still larger initial deformations, transient fission enhancements are possible. Examples of this behavior are illustrated via a one-dimensional Langevin simulation. It is argued that the initial conditions are determined by the fusion dynamics and thus are entrance-channel dependent. Transient fission may be considered intermediate between statistical fission and quasifission as the rapid time scale of transient fission may not lead to an equilibrium of the angular and mass-asymmetry coordinates. The relationship between the mean first passage time and the transients are discussed. For temperatures much smaller than the fission barrier, the mean first passage time is independent of the nature of the fission transients if there is no strong competition from evaporation. Thus, fission transients are most important when the evaporation time scale is smaller than, or of the order of, the transient time.
Transient (computer programming)
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We have calculated the liquid drop fission barriers of medium and heavy nuclei within the Lublin-Strasbourg-Drop model. Exploiting in addition the topographical theorem by Myers and Światecki we propose a simple but quite accurate approximation of the fission barrier heights. When comparing the r.m.s. deviation of approximated versus experimental values of fission barrier heights for known nuclei with Z > 70 a value 1.1 MeV is obtained which is comparable with the experimental uncertainties. The Strutinsky optimal shape method is generalized to the left-right asymmetric shapes of nuclei in order to investigate the influence of this degree of freedom on the barrier heights.
Semi-empirical mass formula
Liquid drop
Nuclear fission
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