Fission of 239Pu with resonance neutrons

A measurement of fission fragment energy and mass distributions in the 239Pu(n, f) resolved resonance region has been performed applying the twin Frisch-gridded ionization chamber technique. An improved pile-up rejection system has been developed to cope with the strong α background.The results for the mass and mean total kinetic energy (TKE) distributions for resolved resonances do not show any strong ‘pattern’ of fluctuations, unlike it was the case for 235U(n, f) in the same neutron energy region. This can be explained in the frame of existing theoretical models, according to which the only possible low-energy spin states available (Jπ=0+, 1+) belong to two well separated (~1.25 MeV) transition state bands with given fission fragment properties. An anti-correlation between TKE and ⊽p was found to be not significant. The obtained small spin dependence of TKE of about 70 keV is in agreement with literature values. A slight correlation was found between TKE versus 1/Γf. But also this was considered not to...