Fission hindrance in hot nuclei

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The role of dynamics in fission has attracted much interest since the discovery of this process over fifty years ago. However, the study of the dynamical aspects of fission was for many years hampered by the lack of suitable experimental observables against which theoretical calculations could be tested. For example, it was found that the total kinetic energy release in fission can be described equally well by very different dissipation mechanisms, namely the wall formula, that is based on the collisions of the nucleons with the moving wall of the system, as well as a bulk viscosity of the nuclear ... continued below

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12 p.

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Back, B.B.; Hofman, D.J. & Nanal, V. July 1, 1997.

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The role of dynamics in fission has attracted much interest since the discovery of this process over fifty years ago. However, the study of the dynamical aspects of fission was for many years hampered by the lack of suitable experimental observables against which theoretical calculations could be tested. For example, it was found that the total kinetic energy release in fission can be described equally well by very different dissipation mechanisms, namely the wall formula, that is based on the collisions of the nucleons with the moving wall of the system, as well as a bulk viscosity of the nuclear matter. Although early theoretical work suggested that the fission process may be described as a diffusion process over the fission barrier, this was largely forgotten because of the success of a purely statistical model which instead of enumerating the ultimate final states of the process argues that the fission rate is determined at the {open_quote}transition state{close_quote} as the system traverses the fission saddle point. It was therefore significant when Gavron showed that the transition state model was unable to describe the number of neutrons emitted prior to scission at high excitation energy in reactions of {sup 16}O+{sup 142}Nd. Subsequent experimental work using different methods to measure the fission dissipation/viscosity has confirmed these initial observations. It was therefore very surprising when Moretto in recent publications concluded that their analysis of fission excitation functions obtained with a and {alpha} and {sup 3}He induced projectiles was perfectly in accord with the transition state model and left no room for fission viscosity. In this paper we`ll show that Moretto`s analysis is flawed by assuming first chance fission only (in direct contradiction to the experimental observation of pre-scission neutron emission in heavy-ion induced fission), and reveal why the systematics presented by Moretto looked so convincing despite these flaws.

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12 p.

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INIS; OSTI as DE97007070

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  • 13. winter workshop on nuclear dynamics, Marathon, FL (United States), 1-8 Feb 1997

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  • Other: DE97007070
  • Report No.: ANL/PHY/CP--92710
  • Report No.: CONF-970271--2
  • Grant Number: W-31109-ENG-38
  • Office of Scientific & Technical Information Report Number: 508113
  • Archival Resource Key: ark:/67531/metadc693791

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  • July 1, 1997

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  • Aug. 14, 2015, 8:43 a.m.

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  • Dec. 16, 2015, 12:30 p.m.

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Back, B.B.; Hofman, D.J. & Nanal, V. Fission hindrance in hot nuclei, article, July 1, 1997; Illinois. (digital.library.unt.edu/ark:/67531/metadc693791/: accessed November 25, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.