Two-quasiparticle states in Cf250 populated by electron capture decay of 8.6-h Es250 isomer

Le résumé fourni par la source

The electron capture decay scheme of the 8.6\ifmmode\pm\else\textpm\fi{}0.1-h $^{250}\mathrm{Es}$ isomer was investigated with high-resolution $\ensuremath{\gamma}$-ray and $\ensuremath{\beta}$-ray spectrometers and with two parameter coincidence analysis. Mass-separated samples of $^{250}\mathrm{Es}$ produced by $^{249}\mathrm{Bk}(\ensuremath{\alpha}, 3n)$ 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 $K\ensuremath{\pi}$ 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 $K\ensuremath{\pi}=2\ensuremath{-} \mathrm{and} 2+$ bands were interpreted as octupole and $\ensuremath{\gamma}$-vibrational bands. The following two-quasiparticle configurations have been assigned: 1255.49 (4-), {$n[734]\frac{9}{2\ensuremath{-}}; n[620]\frac{1}{2+}$}; 1396.18 (5-), {$p[633]\frac{7}{2+}; p[521]\frac{3}{2\ensuremath{-}}$}; 1478.47 (5-), {$n[734]\frac{9}{2\ensuremath{-}}; n[620]\frac{1}{2+}$}; and 1499.62 (6-), {$n[734]\frac{9}{2\ensuremath{-}}; n[622]\frac{3}{2+}$}. The ground state of the 8.6-h $^{250}\mathrm{Es}$ isomer has been given a spin-parity assignment of 6+ with the configuration {$n[734]\frac{9}{2\ensuremath{-}}; p[521]\frac{3}{2\ensuremath{-}}$}. $\mathrm{KLL}$ Auger energies and intensities for $Z=98$ are reported. A $K$ fluorescence yield of 0.976\ifmmode\pm\else\textpm\fi{}0.005 is obtained for Cf.RADIOACTIVITY $^{250}\mathrm{Es}$ [from $^{249}\mathrm{Bk}(\ensuremath{\alpha}, 3n)$ and $^{249}\mathrm{Cf}(d, n)$; measured ${T}_{\frac{1}{2}}$, ${E}_{\ensuremath{\gamma}}$, ${I}_{\ensuremath{\gamma}}$, ${E}_{\mathrm{ce}}$, ${I}_{\mathrm{ce}}$, $\ensuremath{\gamma}\ensuremath{\gamma}$-coin. $^{250}\mathrm{Cf}$ deduced levels, $log\mathrm{ft}$ (EC), $\ensuremath{\gamma}$ multipolarity, $I$, $\ensuremath{\pi}$, four two-quasiparticle states, two vibrational states. Mass-separated $^{250}\mathrm{Es}$. Toroidal $\ensuremath{\beta}$ spectrometer at 0.11% resolution (FWHM).

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