Decay properties of ${}_{97}{}^{243}\mathrm{Bk}$ and ${}_{97}{}^{244}\mathrm{Bk}$

Electron capture decays of ${}^{243}\mathrm{Bk}$ and ${}^{244}\mathrm{Bk}$ have been studied by measuring the $\gamma$-ray spectra of mass-separated sources and level structures of ${}^{243}\mathrm{Cm}$ and ${}^{244}\mathrm{Cm}$ have been deduced. In ${}^{243}\mathrm{Cm}$, the electron capture population to the ground state, $1/2^{+}\left[631\right]$, and $1/2^{+}\left[620\right]$ Nilsson states have been observed. The octupole $K^{\pi }=2^{-}$ band was identified in ${}^{244}\mathrm{Cm}$ at 933.6 keV. In addition, spins and parities were deduced for several other states and two-quasiparticle configurations have been tentatively assigned to them.

Figure 1

Partial decay scheme of ${}^{243}\mathrm{Bk}$ deduced from the present work. The 87.4-keV level was identified in Ref. [7]. $\gamma$-ray intensities are given in relative units and can be converted to photons per ${}^{243}\mathrm{Bk}$ EC decay by multiplying them with 0.121. The total EC intensity in the figure does not add up to 100% because 4.7% belongs to $\gamma$ rays, which are not placed in the level scheme and 9.3% belongs to a tentative 944.9-keV level, not shown in the figure.

Figure 2

Partial decay scheme of ${}^{244}\mathrm{Bk}$ deduced from the present data. The labels shown on the right side of the levels denote the projection $K$ of the total angular momentum $I$ on the nuclear symmetry axis and the parity of the level $\pi$. The $6^{+}$ state at 1040.2 keV was known previously [8]. $\gamma$-ray intensities are given in relative units and can be converted to photons per ${}^{244}\mathrm{Bk}$ EC decay by multiplying them with 0.505. The 1151.1-keV state is given the two-quasiparticle configuration assignment of {$5/2^{+}\left[622\right]\nu \text{;}1/2^{+}\left[631\right]\nu$}${}_{3^{+}}$. The energies of the members of the ground-state band are taken from Ref. [15]. Levels placed on weaker evidence are shown as dashed lines.