The dynamic Monte Carlo (MC) simulation code has been employed to study the primary (the momentum asymmetry) and the secondary (the surface composition gradient) sputter effects on the isotopic enrichment in the isotope  sputtering from the zero to the high fluences, and the static one has been used to study the roles of the primary and the secondary knock-on atoms (the PKAs and the SKAs )  in the zero-fluence isotope sputtering.

In the isotope sputtering from the zero to the high fluences, the dynamic MC simulations show that the difference between the normal isotopic ratio (light  isotope/heavy isotope) and the oblique  isotopic ratio is  positive and  large at both the zero and the high fluences and that this differences is minimized at a low-fluence  between  two fluence limits. The cause is that  during prolonged ion bombardment, the behavior of the angular dependence  of the isopotic ratio vs. sputtering  fluence  is governed by  both the primary and the secondary effects. At very low-influence the primary effects win, while at the high fluence the secondary effects dominate. In between , the two effects can cancel each other.

In the  zero fluence isotope sputtering, the static MC simulations show not only that the normal isopotic ratio (light isotope/heavy isotope) and the difference  between the  normal and the oblique isotopic ratios, are positive and great at low-and high-bombarding-energies; but also that the normal isotopic ratio and its difference increases as the bombarding-energy decreases from high to low energies. The static MC simulations indicate that at high-bombarding-energies (above 1 keV), the momentum asymmetry of the SKAs i.e. the cascade atoms, dominates the isotopic enrichment, generally but a low-bombarding –energies  (below 1 keV), the momentum asymmetry of either the PKAs or SKAs dominates  it.