The Nuclear Stopping subnode is available from the context menu (right-click a Particle-Matter Interactions parent node) or from the Physics toolbar, Attributes menu. Use this subnode to model the deflection of ions by nuclei in the target material. The deflection is modeled using a Monte Carlo model in which the particle velocity can change discontinuously in any time step.

Select an option from the Screening function list: None (the default), Bohr, Moliere, Lenz-Jensen, or Universal. The screening function is the ratio of the electric potential of the target atom to the potential of an unscreened nucleus.

Enter a value or expression for the Cutoff scattering angle χc (SI unit: rad). The default is 0.1°. Any interactions with target nuclei with a scattering angle less than the specified cutoff will be neglected. By specifying a larger cutoff scattering angle, it is possible to ignore interactions that have a small effect on particle momentum, allowing a larger time step to be taken by the solver while still accounting for the more important nuclear collisions (which usually have larger scattering angles).

Select the Count collisions check box to assign an auxiliary dependent variable for the number of collisions with the target material that each particle undergoes. The name of this collision counter is Nc preceded by the scope of the Nuclear Stopping node, for example cpt.pmi1.ns1.Nc.