Pre-fission neutron emission in 19F+209Bi reaction.

The pre- and post-scission neutron multiplicities are measured for ¹⁹F+²⁰⁹Bi reaction at E_lab = 100, 104, 108, 112 and 116 MeV. The measured value of pre-scission neutron multiplicity was found to be increasing with the excitation energy. The comparison of experimental values with the statistical model calculations shows that the measured values are much larger than the model predictions. This difference in excess yield over the model predictions amounts to the survival time of 80±5×10^-21 s for the ²²⁸U compound nucleus before it undergoes fission. [ABSTRACT FROM AUTHOR]