Samples of berkelium and californium have been separated from neutron-irradiated plutonium and carefully purified. Pure ${\mathrm{Cf}}^{249}$ daughter has been separated from the ${\mathrm{Bk}}^{249}$. The californium sample and its curium decay products have been mass analyzed. The berkelium fraction contained 314±8 day ${\mathrm{Bk}}^{249}$ emitting 0.114±0.015 Mev beta particles and 5.417±0.015 Mev and 5.03±0.03 Mev alpha particles. The $\alpha -\beta$ ratio was found to be (2.2±0.3)×${10}^{-5\mathrm{}}$. The californium sample contained: 360±40 year ${\mathrm{Cf}}^{249}$ emitting 5.808±0.010, 5.93±0.02, and 6.20±0.02 Mev alpha particles; 10.9±0.8 year ${\mathrm{Cf}}^{250}$ emitting 6.020±0.010 Mev alpha particles; 800-year ${\mathrm{Cf}}^{251}$; 2.55±0.15 year ${\mathrm{Cf}}^{252}$ emitting 6.112±0.015 Mev alpha particles; and 17±1 day ${\mathrm{Cf}}^{253}$.

• Received 13 June 1957

DOI:https://doi.org/10.1103/PhysRev.107.1635