Absolute photofission cross section of 209Bi in the energy range from 40 to 65 MeV

The absolute photofission cross section of 209Bi has been measured with monoenergetic γ-radiation between 40 and 65 MeV photon energy. Cross-section data have been obtained with an accuracy between 9 and 20%. The experimental result is compared with the excitation function calculated on the basis of the statistical model. In order to reproduce the measured data on sigmasub(γf), the (γ,n) cross section must decrease with increasing photon energy faster than the experimental total (γ,n) cross section. This behaviour can possibly be explained by the assumption that after photon absorption a compound nucleus is formed only for a small, and with photon energy decreasing, fraction of all decays. (orig.)