Introduction

Spontaneous fission (SF) of actinide nuclei provides a means for studying the very neutron rich nuclei centered around the A$\sim$100 and A$\sim$140 mass regions. Spectroscopic information on these nuclei can be obtained by collecting the post-fission de-excitation $\gamma$-rays. Several high statistics experiments have been performed previously in which a source is placed inside a powerful array of $\gamma$-ray detectors, such as Gammasphere or Eurogam, and the $\gamma$-rays of both the fission partners are collected. These experiments have primarily used a source which is thick enough to stop the recoiling fission fragments, so the only information collected is the energy, multiplicity, and relative angles of the $\gamma$-rays. The level diagrams of the nuclei of interest are then deduced from the coincidence relationships of the $\gamma$-rays. Due to the large number of nuclei populated by fission, the $\gamma$-ray density in the collected spectra is high. Additional selectivity is needed to study weak channels and to sort out spectra where $\gamma$-ray coincidences may give ambiguous results. The motivation for this work was to perform a high-statistics experiment in which information about the recoiling fission fragments along with the $\gamma$-rays was collected.