Two-quasiparticle states inCf250populated by electron capture decay of 8.6-hEs250isomer

The electron capture decay scheme of the 8.6±0.1-h ${}_{}{}^{250}{}_{}{}^{}\mathrm{Es}$ isomer was investigated with high-resolution $\gamma$-ray and $\beta$-ray spectrometers and with two parameter coincidence analysis. Mass-separated samples of ${}_{}{}^{250}{}_{}{}^{}\mathrm{Es}$ produced by ${}_{}{}^{249}{}_{}{}^{}\mathrm{Bk}(\alpha , 3n)$ and ${}_{}{}^{249}{}_{}{}^{}\mathrm{Cf}(d, n)$ reactions were used for these measurements. We propose a decay scheme involving 32 transitions and 16 levels in ${}_{}{}^{250}{}_{}{}^{}\mathrm{Cf}$. In addition to the ground state band, six rotational bands have been identified. The energies (keV) and $K\pi$ values of the bandheads are: 871.67 (2-), 1031.80 (2+), 1255.49 (4-), 1396.18 (5-), 1478.47 (5-), and 1499.62 (6-). The $log\mathrm{ft}$ values of the electron capture transitions to the four highest bands were deduced and these were used to elucidate the principal two-quasiparticle components of these states. The $K\pi =2- \mathrm{and} 2+$ bands were interpreted as octupole and $\gamma$-vibrational bands. The following two-quasiparticle configurations have been assigned: 1255.49 (4-), {$n\left[734\right]\mathrm{}\frac{9}{2-}; n\left[620\right]\mathrm{}\frac{1}{2+}$}; 1396.18 (5-), {$p\left[633\right]\mathrm{}\frac{7}{2+}; p\left[521\right]\mathrm{}\frac{3}{2-}$}; 1478.47 (5-), {$n\left[734\right]\mathrm{}\frac{9}{2-}; n\left[620\right]\mathrm{}\frac{1}{2+}$}; and 1499.62 (6-), {$n\left[734\right]\mathrm{}\frac{9}{2-}; n\left[622\right]\mathrm{}\frac{3}{2+}$}. The ground state of the 8.6-h ${}_{}{}^{250}{}_{}{}^{}\mathrm{Es}$ isomer has been given a spin-parity assignment of 6+ with the configuration {$n\left[734\right]\mathrm{}\frac{9}{2-}; p\left[521\right]\mathrm{}\frac{3}{2-}$}. $\mathrm{KLL}$ Auger energies and intensities for $Z=98\mathrm{}$ are reported. A $K$ fluorescence yield of 0.976±0.005 is obtained for Cf.