Experimental Fission Studies at Intermediate Energies

Sammanfattning: A series of nuclear fission experiments have been performed in the intermediate energy range. The dynamics of the fission process have been studied by means of detection of neutrons emitted from compound nuclei formed by ion beams of protons, ?-particles, and 12C-ions, all at a beam energy of 100 MeV. The neutron emission data have been interpreted using a statistical model analysis, and the fission time scale has been found to vary between 6.4 and 170?10-21 s.Neutron-induced fission cross section measurements have been performed on targets of 208Pb, 209Bi, and 238U. The results have been compared with other measurements as well as with model calculations and evaluations. The comparisons agreed reasonably well with previous measurements, but disagreed substantially both with calculations and evaluations. The neutron flux in the neutron-induced fission was determined relative to the np-scattering cross section which was measured simultaneously.The np-scattering cross section has been measured with an unprecedented precision. Using a normalization procedure which takes advantage of the total np cross section, which has been determined with great precision, differential np cross sections have been presented in the angular range 74° to 180° at 96 MeV and 72° to 180° at 162 MeV. They were found to disagree with as much as 10—15 % compared with older measurements in the world data base, and with Partial Wave Analysis solutions. The data are, however, in agreement with another recent, high-quality measurement.