The subbarrier fission probabilities of ${}_{}{}^{234}{}_{}{}^{}\mathrm{U}$, ${}_{}{}^{236}{}_{}{}^{}\mathrm{U}$, and ${}_{}{}^{240}{}_{}{}^{}\mathrm{Pu}$ have been studied using the ($d, \mathrm{pf}$) reaction, with improved statistics over previous measurements. A number of previously unidentified resonances have been found in ${}_{}{}^{236}{}_{}{}^{}\mathrm{U}$ and ${}_{}{}^{240}{}_{}{}^{}\mathrm{Pu}$; in addition, a shelf or plateau from 4.0 to 4.5 MeV in the fission probability of ${}_{}{}^{234}{}_{}{}^{}\mathrm{U}$ has been observed. The fission probabilities have been analyzed using the doorway-state model, and barrier parameters, transition state energies, and the energies of $K^{\pi }=0^{+}$ fission vibrations have been determined. The systematic behavior of transition state and $K^{\pi }=0^{+}$ resonance energies with varying $N$ and $Z$ is discussed.

NUCLEAR REACTIONS, FISSION ${}_{}{}^{233,235}{}_{}{}^{}\mathrm{U}(d, pf)$, ${}_{}{}^{239}{}_{}{}^{}\mathrm{Pu}(d, pf)$, $E_d=11-17\mathrm{}$ MeV, measured $\sigma (E_p, -f \mathrm{coin})$, deduced vibrational spectrum for $E_x=4.0-6\mathrm{}$ MeV.

• Received 16 June 1978

DOI:https://doi.org/10.1103/PhysRevC.18.1706