Damage Production Rate and DPA

A commonly used measure of irradiation damage is displacements per atom (dpa). A unit of 1 dpa means that, on average, every atom in the irradiated volume has been displaced once from its equilibrium lattice site. 

A simple approximation for dpa(.r) per unit dose can be made by assuming that Nd(x), the number of displacements per unit volume at a depth x, can be expressed by a modified Kinchin-Pease expression of the form 

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