Doses from ion sources

Above left, SRIM prediction of damage profile at the total fluence of about 1.3x1017 Xe/cm2 with 300 keV Xe beam irradiation. A plateau can be perceived at around 250 dpa, the consequence of significant sputtering. At 300 keV ion beam irradiation (e.g., IVEM Tandem), it can be safely concluded that the accumulated damage anywhere inside the target Mo material would not exceed 300 dpa no matter how much fluence is reached by the end of the irradiation.

Above right, SRIM prediction of damage profile at the total fluence of about 8.8x1017 Xe/cm2 with 100MeV Xe beam irradiation. For the much higher energy 100MeV Xe beam case (e.g., XMAT), the damage profile is pushed well into the material target. It is clear that damage levels in excess of 600 dpa can be reached with a fluence of about 8.8x1017 Xe/cm2 in a rather wide range of material depth.

The maximum dose (DPAs) that can be induced in a solid by an external ion source is a competition between the per ion surface removal rate (sputtering) and the per ion damage rate (DPA/ion). Maximum dose calculations must take into account the removal rates for MeV/nucleon ions, but limited data is available.

Sputtering yields range from 5-10 atoms/ion for metals.* For compound phase transformations such as evaporation, higher yields are possible. In these cases, a metal coating may be effective. Chemical effects such as those found on H on graphite may also play a role in increased yields.**

*Mieskes et al (1998). "Measuring sputtering yields of high energy heavy ions on metals." Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions of Materials and Atoms 146(1-4): 162-171.

**Gordillo et al (2012). "Stopping power dependence of nitrogen sputtering yields in copper nitride films under swift-ion irradiation: Exciton model approach." Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions of Materials and Atoms 289(0): 74-78.