Neutron multiplicity measurements of Cf and Fm isotopes

Prompt neutrons in coincidence with the fission fragments from the spontaneous fission of 250,252,254Cf and ²⁵⁷Fm were measured inside a 75-cm-diameter, Gd-loaded liquid scintillation counter having a neutron-detection efficiency of about 78%. Measurements for ²⁵⁶Fm were done just outside the counter with an efficiency of 31%. The kinetic energies of both fission fragments and the number of neutrons for each fission event were recorded. From these data, the fragment kinetic energies and masses and the neutron multiplicity distributions were determined for 250,252,254Cf and ²⁵⁷Fm. Variances of neutron multiplicity distributions as a function of total fragment kinetic energy and the ratio of fragment masses have been calculated and are presented for all the nuclides studied.RADIOACTIVITY, FISSION 250,252,254Cf, ²⁵⁷Fm; measured neutron multiplicity distributions as a function of total kinetic energy and mass ratio. ²⁵⁶Fm; measured average and variance of neutron multiplicity distributions as a function of total kinetic energy and mass ratio.