Decay of 25-MinAm246and 1.8-DayBk246

The radiations associated with the $\beta$ decay of 25-min ${\mathrm{Am}}^{246}$ and the electron-capture decay of 1.8-day ${\mathrm{Bk}}^{246}$ have been studied with $\gamma$-scintillation spectrometers, Ge(Li) detectors, and a Au-surface-barrier electron detector. Conversion-electron lines of the more intense ${\mathrm{Cm}}^{246}$ transitions have been observed and tentative multipole orders have been assigned. A decay scheme is presented on the basis of $\gamma$-ray energy and intensity data, $\gamma -\gamma$ coincidence studies, and conversion-electron measurements. The ${\mathrm{Cm}}^{246}$ level diagram includes excited states at 43, 142, 843, 878, 1078, 1106 1126 (doublet), 1318, 1352, 1369, 1483, 1531, 1598, 1643, ≥1668, and ≥1739 keV. The levels at 843, 878, 1078, 1106, and 1126 (doublet) keV are all directly populated by both 25-min ${\mathrm{Am}}^{246}$ and 1.8-day ${\mathrm{Bk}}^{246}$. The 1126-keV doublet level consists of the $I=3\mathrm{}$ rotational member of a $K^{\pi }=1^{-}$ band based at 1078 keV and a $2^{+}$ state that de-excites by essentially pure $E2\mathrm{}$ transitions to the $0^{+}$ and $2^{+}$ members of the ground-state band. Consideration of the electron-capture decay information and available Nilsson orbitals leads to a spin and parity assignment of $2^{-}$ for 1.8-day ${\mathrm{Bk}}^{246}$. The present work is in agreement with the previous $2^{+}$ assignment for 25-min ${\mathrm{Am}}^{246}$.