Accurate Determination of (n,2n) Cross Sections for Heavy Nuclei from Neutron Production Spectra

It is demonstrated that (n,2n) cross sections for many medium-mass and heavy nuclei can be determined with high accuracy (∼3%) from existing data on nonelastic cross sections and energy-differential neutron emission cross sections. Using this method, the (n,2n) cross sections for ⁹³Nb, ²⁰⁹Bi, and the natural elements tantalum, tungsten, and lead are determined for a neutron energy of 14 A MeV. There is reasonable agreement with the existing measurements; however, our results considerably reduce the uncertainties of these cross sections. For lead, which is especially important as a possible neutron multiplier material in fusion reactors, the accuracy requested for this purpose is achieved. It is further demonstrated that the peak values of the (n,2n) excitation functions for heavy nuclei (A > 190) show a very smooth behavior with mass number, which allows prediction of unknown (n,2n) cross sections with accuracies better than 3%.