Lawrence Berkeley National Laboratory

Experiments conducted at Lawrence Berkeley National Laboratory's 88-Inch Cyclotron Facility aimed to produce and study the decay of the previously unobserved isotope Db255. This isotope was produced in the Pb206(V51, 2n)Db255 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 Db255 were determined from the analysis of evaporation residue (EVR) fission and EVR-α-α correlations. The properties of this new isotope of dubnium differ dramatically from those of its neighboring Db isotopes. Db255 was found to decay primarily by spontaneous fission (SF) with a small α-decay branch, where the average half-life of the observed decays was t1/2=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.