Calculations of defect production, eqn [2], require knowledge of the damage function, n(T). While it is not possible to measure this function directly, as no irradiation creates monoenergetic recoils except near the surface, it can be obtained by measuring defect production for a wide range of ion irradiations and subsequently deconvoluting eqn [3]. Low-energy light ions, for example, weight the recoil spectrum near the threshold energy, «25-100 eV, while more energetic heavy ions weight it at high energies. Results are shown for Cu in Figure 13. Here, electri­cal resistivity measurements are employed to monitor the absolute number of FPs produced per unit dose of irradiation. Included in this figure are the damage efficiency function, X(T1/2), deduced from the experi­ments and X(T) calculated using molecular dynamics computer simulation. The damage efficiency function is defined as

v(T ) = £(T )vNRT (T), [20]

where nNRT(T) is the NRT damage function defined by eqn [1]. The good agreement between experiment and simulations illustrates that the damage function in Cu is now well understood. This is now true for many other pure metals as well.24 In alloys and ceramic

materials, however, the damage function remains poorly known.