Experiments conducted at Lawrence Berkeley National Laboratory's 88-Inch Cyclotron Facility aimed to produce and study the decay of the previously unobserved isotope ${}^{255}\mathrm{Db}$. This isotope was produced in the ${}^{206}\mathrm{Pb}({}^{51}\mathrm{V}, 2n){}^{255}\mathrm{Db}$ reaction, separated from unreacted beam material and reaction by-products with the Berkeley Gas-filled Separator, and then implanted into a double-sided silicon-strip detector at the BGS focal plane. Decay properties of ${}^{255}\mathrm{Db}$ were determined from the analysis of evaporation residue (EVR) fission and EVR-$\alpha \text{−}\alpha$ correlations. The properties of this new isotope of dubnium differ dramatically from those of its neighboring Db isotopes. ${}^{255}\mathrm{Db}$ was found to decay primarily by spontaneous fission (SF) with a small $\alpha$-decay branch, where the average half-life of the observed decays was $t_{1/2}=2.6_{-0.3}^{+0.4}$ ms. Theoretical calculations were performed using the Wentzel-Kramers-Brillouin approximation, with parameters calculated within a self-consistent microscopic approach, to see if these unique properties could be reproduced. A SF half-life estimate is obtained that closely matches the measured value, while simultaneously pointing out the sensitivities that need to be further constrained in future work.

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• Fission
• Rare & new isotopes
• A ≥ 220
• Spectrometers & spectroscopic techniques