Viscosity of saddle-to-scission motion in hot 240Cf from giant dipole resonance gamma yield.

Abstract

The giant dipole resonance \ensuremath{\gamma} decay of $^{240}\mathrm{Cf}$ excited to 67 and 93 MeV was measured from the fusion of $^{32}\mathrm{S}$${+}^{208}$Pb. The \ensuremath{\gamma} spectrum and \ensuremath{\gamma}-fission angular correlation are analyzed in terms of prefission and postfission \ensuremath{\gamma}-ray yields using a stattistical model with nuclear viscosity in the fission process. The results show a strong increase in the prescission \ensuremath{\gamma} yield from 67 to 93 MeV. A saddle to scission time ${\mathrm{\ensuremath{\tau}}}_{\mathrm{s}\mathrm{s}\mathrm{c}=}$30\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}21}$ s is extracted from this \ensuremath{\gamma} yield, equivalent to a normalized viscosity \ensuremath{\gamma}\ensuremath{\approxeq}5 and full one-body dissipation.