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Neutron induced fission and total cross sections of "-"U have been measured over the neutron energy range from a few eV to 8.9 MeV. Neutron and fission widths for 118 cross section resonances below 1500 eV have been determined and give a class I level spacing of ]0.6+0.5 eV and an s-wave strength function of (0.86+ 0.11) g 10 '. These fine structure resonances form two narrow intermediate structure resonances in the subthreshold fission cross section of '"U. Parameters for the Lorentzian energy dependence of the mean fission width are deduced by maximum likelihood analysis on the assumption that, relative to this mean, the observed fission widths have a Porter-Thomas distribution. Two large fission widths measured for resonances at 1092.5 and 1134 eV prompted a likelihood ratio test which indicates the presence of a narrow irtermediate structure resonances at 580 and at 1227 eV. The class II level spacing derived from the observation of seven intermediate structure resonances below 14 keV is 2. 1 + 0.3 keV. Broad structures in the fission cross section at 310, 550, and 770 keV are assumed to be due to P-vibrational levels in the second minimum of the Strutinsky potential. Fluctuations due to the presence of class II resonances are strongly evident for each of these vibrational levels. It is shown that the fluctuations near 310 keV are consistent with parameters deduced from the!ow energy data and this allows parameters for the double humped fission barrier potential to be obtained.

The periods, yields and energies of the delayed neutrons from fission of U 235 have been measured with a pneumatic transfer apparatus ("rabbit") at the heavy water pile of the Argonne Laboratory. The following periods account for the saturated decay curve of delayed neutrons for times longer than 0.02 sec. after irradiation ceases:Yield (relative to total neutron Half-life Energy emission)

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