Cross section empirical formulation for (n, 2n) nuclear reactions on natural from Z=21 to Z=79 for neutron 8-20 MeV

Neutron induced reactions with different target materials and isotopes are very important for completion of nuclear data base as well as for many applications. Since the experimental determinations of the reaction cross sections for such reactions are not always available, attempts were made to introduce empirical or semi empirical formulae. In this work, new empirical formulation for (n, 2n) nuclear reactions on natural isotopes for neutron energies range 8-20 MeV, based on some published experimental works. The deuced formulae are then used to calculate the excitation functions for the (n,2n) on target isotopes having atomic numbers in the range 21-79. The cross section values for many reactions, having previously measured values, are determined and intercomparison with the experimental and the TENDL-2019 database values are given using some statistical error parameters. Special attention was made to some Lanthanide isotopes. The results showed satisfied predictions in most cases.