Two new isotopes of californium have been identified through bombardments of ${}_{}{}^{235}{}_{}{}^{}\mathrm{U}$, ${}_{}{}^{234}{}_{}{}^{}\mathrm{U}$, and ${}_{}{}^{233}{}_{}{}^{}\mathrm{U}$ with ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ ions from the Oak Ridge isochronous cyclotron. They decay with half-lives of 3.78 ± 0.70 and 1.06 ± 0.15 min and with the emission of $\alpha$ particles of 7.335 ± 0.005 and 7.590 ± 0.010 MeV, respectively. Analysis of the excitation functions for these $\alpha$ emitters favors the assignment of mass 241 to the former and mass 240 to the latter; also, the 7.335-MeV activity was shown to be chemically similar to californium. New values for the $\alpha$-particle energies of ${}_{}{}^{242}{}_{}{}^{}\mathrm{Cf}$ were obtained: 7.385 ± 0.004 and 7.351 ± 0.006 MeV, assigned, respectively, to $\alpha$-decay transitions to the ground and first excited states of ${}_{}{}^{238}{}_{}{}^{}\mathrm{Cm}$.

• Received 20 July 1970

DOI:https://doi.org/10.1103/PhysRevC.2.1948