Recently I came across evidence that during 1941 leading Japanese nuclear physicists B.Arakatsu and S.Simizu, were working on proton bombardment of Lithium or Fluorine to transmute Thorium and Uranium.
Farm Hall transcripts disclose that Nazi scientists were also working on this during WW2.
My question is what are the transmutation steps from Uranium 238 to Plutonium 239?
Does the Uranium 238 simply adopt a slow neutron and become Plutonium 239 or is there an intermediary step for example through Neptunium?