MOMENTUM IN ATOMIC COLLISION CASCADES

The problem of the spatial distribution of momentum deposited in atomi c collision cascades has been revisited. Particular attention has been paid to the scaling and symmetry properties of this distribution whic h are more complex than those of the deposited-energy density or the i on range, The use of two length units with different dependencies on r ecoil and ion energy is essential. This results in a splitting of the deposited-momentum profile into two contributions with different symme tries. One of these accounts for momentum conservation while the other one represents momentum diffusion. Calculated momentum profiles show excellent agreement with results from Monte Carlo simulations on equiv alent systems. Deposited momentum is known to be closely related to th e anisotropy of the particle flux in a collision cascade. The quantita tive connection has been studied. While the former quantity can be exp ressed rigorously in terms of the latter, we have so far only found an approximation for the inverse relationship, i.e., an expression of th e angular flux in terms of deposited energy and momentum. This express ion, too, contains a diffusive term, the symmetry properties of which differ from the previously known anisotropy correction.