Observation of the Shape Isomer States in Fission Fragments from (γ, F ) Reactions

The binary break-up of heavy fission fragments from the 235,238 U(γ, f ) reactions, while the fragments cross a solid medium, were observed for the first time. The experiments were performed at the beam of the M-T‑25 microtron at the Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, using VEGA (V-E Guide based Array) setup. Fission fragments were captured by the electrostatic guide system four meters long and transported in the time-of-flight spectrometer. The results let us to suppose that the fragments undergoing the break-up were born in the shape isomer states with a typical lifetime of more than 400 ns.