Multilevel Analysis of thePu239Fission Cross Section from 14 to 90 eV

The ${}_{}{}^{239}{}_{}{}^{}\mathrm{Pu}$ fission cross section has been fitted with a multilevel $R$-matrix formula from a neutron energy of 14 to 90 eV. Spin assignments have been made from the interference between resonances. The average fission widths are 1033 meV with at least two open fission channels for the $0^{+}$ spin state, and 66 meV and one channel for the $1^{+}$ state. The number of undetected levels is deduced from the statistical distributions of resonance parameters.