MEASUREMENTS OF ABSOLUTE DELAYED NEUTRON YIELD AND GROUP CONSTANTS INTHE FAST FISSION OF U-235 AND NP-237

The delayed neutron activity resulting from the fast induced fission o f U-235 and Np-237 has been studied. The sir-group decay constants, re lative abundances, and absolute yield of delayed neutrons from fast fi ssion of U-235 and Np-237 were measured using the Godiva IV fast assem bly at the Los Alamos Critical Experiment Facility. The absolute yield measured for U-235 was 0.0163 +/- 0.0008 neutron/fission. This value compares very well with the well-established Keepin absolute yield of 0.0165 +/- 0.0005. The absolute yield value measured for Np-237 was 0. 0126 +/- 0.0007. The measured delayed neutron parameters for U-235 are corroborated with period (e-folding time) versus reactivity calculati ons.