A diffusion model calculation of axial blocking dips of α-particles in aluminium

Angular blocking dips around the ⟨110⟩ axis in Al single-crystal of α-particles of about 2 MeV produced at a depth of 0.2 μm are calculated for the following values of the mean displacement v υ ⊥ τ of the decaying nucleus: v υ ⊥ τ = 0,4.4, 13, 30 pm. Calculations have been made on the basis of a continuum model with diffusion, where the effects of multiple scattering on the transverse energy distribution are taken into account by means of a diffusion equation as originally suggested by Lindhard. The results are compared with the blocking dips obtained through an extensive Monte Carlo calculation where the lattice atoms are allowed to vibrate. The agreement between the results of these two methods is very satisfactory. Significantly different results are obtained if the blocking dips are calculated according to the continuum (or halfway-plane) model without diffusion.