Abstract
The reaction mechanism of 19F + 232Th and 28Si + 232Th systems populating the near-super-heavy compound nuclei 251Es and 260Rf respectively are investigated using neutron multiplicity as a probe. The prescission neutron multiplicities of these compound nuclei are calculated at different excitation energies using a statistical model code. These calculations are performed using the Bohr-Wheeler transition state fission width as well as the dissipative dynamical fission width based on the Kramers’ prescription. For 19F + 232Th system, the measured yield of pre-scission is compared with the statistical model calculations for the decay of a compound nucleus in the excitation energy range of 54-90 MeV. The comparison between the measured and the calculated values indicates that the Bohr-Wheeler fission width underestimates the pre-scission neutron yield and a large amount of dissipation strength is required to reproduce the experimental pre-scission neutron multiplicities. The excitation energy dependence of the fitted values of the dissipation coefficient is also discussed. In addition, exploratory statistical model calculations of pre-scission neutron multiplicity for the 28Si + 232Th system are presented in the above range of excitation energy.
Highlights
The importance of neutrons as a probe for fusionfission dynamics was first pointed out in a series of earlier pioneering works
We present results of statistical model calculation in order to explore the role of dissipation in pre-scission neutron multiplicities of 19F + 232Th and 28Si + 232Th systems
The calculated BW fission widths for both the compound nucleus (CN) 251Es and 260Rf at different excitation energies and values are shown in figure 1
Summary
The importance of neutrons as a probe for fusionfission dynamics was first pointed out in a series of earlier pioneering works (e.g. see [3,4,5,6]). These works established that fission becomes a slow process in comparison to the transition-state theory of Bohr and Wheeler [7] beyond a certain excitation energy for heavy compound nuclei. We present results of statistical model calculation in order to explore the role of dissipation in pre-scission neutron multiplicities of 19F + 232Th and 28Si + 232Th systems.
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