Significant work has been performed on the development of STEFF (SpecTrometer for Exotic Fission Fragments), a 2E2V (2-Energy 2-Velocity) spectrometer built by the University of Manchester Fission Group. The majority of this work was in the development of the time-of-flight systems, in particular the stop detector; with the main goals of improving the timing resolution and the detection effciency of the fission fragments. Further development of the STEFF spectrometer was done to enable 2E2V measurements of the 235U(n,f) reaction with coincident measurements using a white neutron spectra of energies ranging from 10 meV to200 MeV provided by the n TOF (neutron Time Of Flight) facility, CERN. The STEFF spectrometer was successfully operated twice on the Experimental Area-2 high flux pulsed neutron beam line resulting in 2E2V measurements for fission events with neutron energies ranging from 20 meV to 10 MeV. The first experiment received 1.36x10^18 POT (Protons On Target) with stable conditions and the second received 1.53x10^18 POT with stable conditions. The development of the stop detector resulted in a replacement MWPC (Multi-Wire Proportional Counter) detector for the second of the two experiments. This allowed direct comparison for the timing coincidence resolution, sigma_c, between the start and stop detectors and gave sigma_c = 0.81+/-0.08 ns for the prior PPAC (Parallel Plate Avalanche Counter) detector and sigma_c = 0.40 +/- 0.04 ns for the MWPC. The MWPC gave improved the detection efficiency per fission fragment of Eff = 0.67 compared to Eff = 0.43 for the PPAC. The methods and research described in this work also provided alternate stop detector designs with greater performance. This work produced two large data sets from the two successful deployments of the STEFF spectrometer on the n TOF beam line that will be the future work of many nuclear structure scientists to come.

No abstract provided. / Thesis / Master of Science (MSc) / Scope and contents: The probability of fission as a function of primary fragment velocities has been obtained by removing the neutron emission and instrumental dispersions from the velocities determined by Stein with time-of-flight techniques for the thermal neutron fission of u235. Each velocity was increased by 0.69% to make the average kinetic energy per fission agree with the calorimetric value of 167.1 Mev. Excitation energy distributions were obtained by using the primary fragment masses given by Cameron and assuming that the most probable charge distribution for a given mass ratio i s that which leads to the greatest energy release. Evaporation theory was used to determine the number of prompt neutrons emitted. When the excitation energy is divided equally between the fragments and a nuclear temperature of 0.59 Mev is used, the average number of neutrons emitted is 2.95 per fission.