Cascade morphology transition in bcc metals

Energetic atom collisions in solids induce shockwaves with complex morphologies. In this paper, we establish the existence of a morphological transition in such cascades. The order parameter of the morphology is defined as the exponent, \(b\), in the defect production curve as a function of cascade energy (\(N_F \sim E_{MD}^b\)). Response of different bcc metals can be compared in a consistent energy domain when the energy is normalized by the transition energy, \(\mu\), between the high- and the low-energy regime. Using Cr, Fe, Mo and W data, an empirical formula of \(\mu\) as a function of displacement threshold energy, \(E_d\), is presented for bcc metals.