A Monte Carlo Code for Radiation Damage by Neutrons

A Monte Carlo code is developed in Visual Basic 6.0 for the study of radiation damage of pure metals irradiated by a neutron spectrum. At energies <10 MeV, development of cascades of elastic interactions of both primary neutrons and secondary recoiled atoms is incorporated. In a collision, kinetic energy given to an atom below or above the threshold displacement energy E-d (eV) is calculated along with the displacements. Displacements, defect production efficiency eta, and damage energy T-dam are estimated to relate to the physical changes in the irradiated metal and to estimate the displacements per atom. The code is validated by determining the defect density on the surface of irradiated thin nickel foil and comparing with the hill-hock density of displaced atoms, using atomic force microscopy. In the case of irradiation of a niobium sample, stress-strain and I-V characteristics are measured before and after the irradiation by neutrons from an Am-Be source, and both stress and electrical resistance are shown to be enhanced after the irradiation.