Mass Assignment of the 44-Minute Californium-245 and the New Isotope Californium-244

The 44-minute californium alpha emitter previously thought to be ${\mathrm{Cf}}^{244}$ has been reassigned to mass number 245 on the basis of milking experiments, excitation functions, cross bombardments, and decay-scheme studies. Californium-245 decays by the emission of (7.11±0.02)-Mev alpha particles (∼30%) and by orbital electron capture (∼70%). The new isotope ${\mathrm{Cf}}^{244}$ was also identified and found to decay by the emission of (7.17±0.02)-Mev alpha particles with a half-life of 25±3 minutes. The mass assignment of this isotope was established by its genetic relationship to ${\mathrm{Cm}}^{240}$ and by the excitation function for its formation by the ($\alpha , 4n$) reaction on ${\mathrm{Cm}}^{244}$.