The new isotope 12.3-min ' Cf was produced via the ' Cf(t,p) reaction, and a new 43-min isomer of ' Md was produced via the ' Es(a,n) reaction. The fragment mass and kinetic energy distributions from the spontaneous fission of" Cf were found to be very similar to those from the spontaneous fission of lighter Cf isotopes. The mass division is primarily asymmetric, and the average total kinetic energy is 189.8+0.9MeV. The 43-min "Md presumably decays by electron capture and provides an opportunity to study the mass and kinetic energy distributions from the spontaneous fission of. the 380-p,s Fm daughter. The observed narrow, symmetric mass distribution and the most probable total kinetic energy of 238+3 MeV are similar to those reported for the spontaneous fission of" Fm but show a sharp increase in symmetric mass division and total kinetic energy compared to Fm and the lighter Fm isotopes. No such abrupt change in properties was observed for "Cf, which, like "Fm, has 158 neutrons. The marked difference between the spontaneous fission properties of the heavier Fm isotopes and those of other spontaneously fissioning nuclides is compared to some theoretical predictions.
RADIOACTIVITY, FISSIONCf (SF); measured T&~&, fragment-fragment coin; deduced TKE, mass distribution. Md; measured''~g2, . EC decay to 5 Fm (SF); measured fragment-fragment coin; deduced TKK, mass distribution.
Fission probabilities and mass distribution have been measured as a function of excitation energy for "'Ra excited in the ' Ra(t, pf) reaction. Triple peaked mass distributions are observed for which the symmetric component has an apparent higher threshold by over 1 MeV. Results are analyzed in a statistical model which suggests the presence of a resonance in the fission probability for the asymmetric mass component and the need for level density enhancements (possibly due to axial asymmetry at the barrier) in the analysis of the fission probability for the symmetric component.
NUCLEAR REACTIONS, FISSIONRa(t, Pf ); measured fission probabilities for symmetric and asymmetric components; deduced fission barrier parameters, fission mass distributions.
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