Alpha-gamma decay studies of $^{258}$Db and its (grand)daughter nuclei $^{254}$Lr and $^{250}$Md
Résumé
The superheavy isotope$^{258}$Db was produced in the$^{209}$Bi($^{50}$Ti, 1n)$^{258}$Db reaction at GSI, Germany. A detailed $ \alpha$ -spectroscopy study of this isotope and its $ \alpha$ -decay daughter products was performed. Two long-lived $ \alpha$ -decaying states in$^{258}$Db are observed. A spin-parity of $ 0^{-}$ is tentatively assigned to the ground state for which a half-life of $ 2.17 \pm 0.36$ s is determined. Spins and parities of either $ 5^{+}$ or $ 10^{-}$ are proposed for the isomeric state found at an excitation energy of 51 keV with a half-life of $ 4.41 \pm 0.21$ s. The $ \alpha$ -decay daughter isotope$^{254}$Lr displays a similar behavior. A half-life of $ 11.9 \pm 0.9$ s is determined for the$^{254}$Lr ground state which is tentatively assigned a spin-parity of $ 4^{+}$ . The isomeric level of this isotope placed at 108 keV with a half-life of $ 20.3 \pm 4.2$ s is tentatively assigned a spin-parity of $ 1^{-}$ . Two long-lived $ \alpha$ -decaying states are observed in the granddaughter isotope$^{250}$Md . The ground state has a half-life of $ 59.5 \pm 9.1$ s. A half-life of $ 42.4 \pm 4.5$ s is measured for the isomeric state positioned at an excitation energy of 123 keV. Partial, tentative level schemes for$^{254}$Lr,$^{250}$Md and$^{246}$Es are proposed based on the $ \alpha$ - $ \gamma$ coincidences.