Collisions between charged particles in a plasma are usually considered as Coulomb collisions with small fractional energy exchange and small scattering angles. However, high-energy particles can participate in close collisions with a large energy exchange when the minimum distance of approach between particles is such that the strong nuclear force comes into play. Theoretical and experimental studies of this effect showed that Nuclear Elastic Scattering (NES) of energetic a-particles with thermal ions forms MeV energy range deuterium and tritium tails, which can give a significant contribution to the a-particle signal on a Neutral Particle Analyser (NPA).