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

• Received 15 June 1993

DOI:https://doi.org/10.1103/PhysRevLett.72.470