Reexamination of fission in the A≈200 mass region with excitation energy near 50 MeV

Abstract

Even though the fission of nuclei in the mass region 200 with excitation energy near 50 MeV has been studied extensively, a unique description of the fission probability and prefission neutron multiplicity (${\ensuremath{\nu}}_{\mathrm{pre}}$) data remains elusive. In the present work, a reexamination of the relevant data along with a new estimate of ${\ensuremath{\nu}}_{\mathrm{pre}}$ and fission chance distributions, obtained from the experimental fission excitation functions of neighboring Po isotopes, has been carried out. The ${\ensuremath{\nu}}_{\mathrm{pre}}$ from the above-mentioned method, sensitive to only the presaddle part, is significantly lower than the value obtained from neutron spectra measurements. Further, ${\ensuremath{\nu}}_{\mathrm{pre}}$ from the fission chance data is in good agreement with the statistical model predictions, which also accounts for the light-ion induced fission probability data up to low excitation energy ($\ensuremath{\sim}30$ MeV). From this observation, it is concluded that the presaddle dynamical effects are not significant over this excitation energy range, and the ${\ensuremath{\nu}}_{\mathrm{pre}}$ data determined from the neutron spectra might have a significant contribution from the near-scission emission.