Study of Interatomic Potentials Using the Crystal-GRID Method on Oriented Single Crystals of Ni,Fe, and Cr

The Crystal-GRID method is used to study interatomic collisions at low energy in metals and such to probe the repulsive interatomic potential. Line shapes of gamma rays, emitted by the recoiling ⁵⁹Ni isotope after thermal neutron capture in Ni single crystals, were measured and compared to results obtained by molecular dynamics simulations of the slowing down. The same procedure is also used for recoiling ⁵⁷Fe and ⁵⁴Cr atoms in Fe and Cr single crystals, respectively. Different potentials (including several from the embedded atom method) are investigated using the observed fine structure of the line shape which depends on the crystal orientations. From the detailed study of the lineshapes measured in two different orientations, a new potential is then derived for each element. Nuclear state lifetimes for the excited isotopes are also deduced with a higher precision than obtained with standard nuclear techniques.