INTERNATIONAL VALUES FOR THERMAL CROSS SECTIONS OF FISSILE ISOTOPES

At session 17 A*) of the International Conference on the Peaceful Uses of Atomic Energy, a large amount of declassified data was presented on the effective neutron cross sections of the fissile isotopes U-233, U-235, and Pu-239. In the low-energy region, where a large number of measurements were reported, excellent agreement was obtained among the data for these isotopes, which play an important role in reactor systems. At the initiative of the Chairman, scientists from France, the United Kingdom, the Union of Soviet Socialist Republics, and the United States met after the official session to consider the thermal \((2200\ \text{m/sec})\) effective absorption and fission cross sections of these isotopes. It was decided to develop a system of international mean values for these effective cross sections, which would promote agreement among reactor calculations based on these constants. The adopted errors of the international mean cross sections given here are based directly on the spread of the reported results and are somewhat larger than the errors of some individual measurements.

*) Session 17 A, August 17, 1955: “Effective Cross Sections of Fissile Isotopes,” chairman D. Hughes (USA), vice-chairman D. Popovich (Yugoslavia).