Electrofission of239Puin the energy range 7–12 MeV

Abstract

The electrofission cross section of ${}^{239}\mathrm{Pu}(e,f)$ is measured between 7 and 12 MeV. The data are analyzed by means of the virtual photon formalism, assuming that $E1,$ $E2$ $(T=0),$ and $M1$ transitions are involved. Using known estimates for the $E1$ and $E2$ $(T=0)$ fission strengths, it is deduced an $M1$ fission strength of $19\ifmmode\pm\else\textpm\fi{}4{\ensuremath{\mu}}_{N}^{2}$ concentrated near the fission barrier (between 5.4 and 5.8 MeV). The levels of the ${}^{239}\mathrm{Pu}$ transition nucleus are theoretically obtained; a bunch of positive-parity levels shows up between 5.5 and 5.9 MeV, which might well be associated with the deduced $M1$ strength, since the $E2$ strength is negligible in this energy interval.