Fission hindrance in hot nuclei
Back, B.B.; Hofman, D.J.; Nanal, V.
Argonne National Lab., IL (United States). Funding organisation: USDOE Office of Energy Research, Washington, DC (United States)1997
Argonne National Lab., IL (United States). Funding organisation: USDOE Office of Energy Research, Washington, DC (United States)1997
AbstractAbstract
[en] 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 16O+142Nd. 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 α and 3He 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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1997; 12 p; 13. winter workshop on nuclear dynamics; Marathon, FL (United States); 1-8 Feb 1997; CONF-970271--2; CONTRACT W-31109-ENG-38; Also available from OSTI as DE97007070; NTIS; US Govt. Printing Office Dep
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