Global and partial cross sections
The apparent sizes as seen by neutron of three heavy nuclei, uranium-235, uranium-238 and plutonium, are represented on the figure by shooting targets. Target areas represent total cross sections, central parts radiative neutron captures, red band captures followed by fission. One can see that in the two energy ranges of neutrons called thermal and intermediate, the global and partial cross-sections areas are extremely different for the three nuclei. : capture and fission uranium-238 cross sections are much smaller than that of uranium-235 and plutonium-239.
IN2P3