Sensitive search for near-symmetric and super-asymmetric fusion-fission of the superheavy element Flerovium (Z=114)

Measurements of mass and angular distributions have been made for fission-like outcomes in reactions forming isotopes of flerovium (Z=114), using ⁴⁸Ca, ⁵⁰Ti, and ⁵⁴Cr projectiles. The dominant fast quasifission process, which masks the presence of fusion-fission, has minimum yield at the most backward angles, where the sensitivity to fusion-fission is thus highest. In fitting the backward angle mass spectra, only weak evidence for a component of super-asymmetric fission was found, but a near-symmetric fission component was consistently required for the ⁴⁸Ca + ²⁴⁴Pu reaction, giving upper limit to the fusion probabilities $P_{CN}$ of ∼10⁻², ∼5 times lower than previous results. $P_{CN}$ for the ⁵⁰Ti reaction was lower than ⁴⁸Ca, whilst no evidence of fusion-fission was found for the ⁵⁴Cr reaction.