Nuclear rotation at the fission limit in $254$$\mathrm{Rf}

Here, a ground-state rotational band in the fissile nucleus 254Rf was observed for the first time. Levels up to spin 14$\hbar$ and excitation energy of 1.56 MeV were observed. The 254Rf nuclei were produced using the 206Pb(50Ti, 2n) fusion-evaporation reaction. It is the weakest reaction channel ever studied using in-beam $γ$-ray spectroscopic methods. The reaction products were separated from the beam in the Argonne gas-filled analyzer (AGFA). The 254Rf nuclei were implanted into a double-sided Si strip detector at the AGFA focal plane and tagged with subsequent ground-state spontaneous fission decays using temporal and spatial correlations. Prompt $γ$ rays in coincidence with the 254Rf recoils were detected in the Gammasphere array of Ge detectors. In order to identify the ground-state rotational band in 254Rf, a method for identifying rotational bands in low statistics $γ$-ray spectra was developed. The deduced 254Rf kinematic moment of inertia is smaller compared to neighboring even-even nuclei. This is most likely associated with a slightly lower quadrupole deformation and stronger pairing correlations in 254Rf. The behavior of the moment of inertia as a function of rotational frequency is similar to that of the lighter N = 150 isotones 250Fm and 252No.