The beta decay of ${\mathrm{Bk}}^{250}$ has been studied with a beta spectrometer. ${\mathrm{Bk}}^{250}$ has two beta groups: 725±15 kev (89±1% abundant) and 1760±50 kev (11±1% abundant). Conversion electron lines corresponding to 42.2, 98.2, 890, 930, 990, and 1032-kev transitions were observed and their intensities measured. The information obtained from crystal spectrometer singles and coincidence measurements was combined with beta spectrometer data to construct a decay scheme for ${\mathrm{Bk}}^{250}$ involving gamma vibrational levels in ${\mathrm{Cf}}^{250}$ analogous to those found in ${\mathrm{Pu}}^{238}$. The beta half-life of ${\mathrm{Bk}}^{250}$ is 193.3±0.3 minutes. The electron capture partial half-life of ${\mathrm{Bk}}^{250}$ is estimated to be greater than 50 hours. The beta spectrum of ${\mathrm{Bk}}^{249}$ shows an allowed or first-forbidden transition with an end-point energy of 125±2 kev.

• Received 4 February 1959

DOI:https://doi.org/10.1103/PhysRev.115.115