A simple model, based on the diffusion of impurity particles in the momentum space, is presented to simulate the distribution of laser blow-off injected aluminium species in the plasma of the MT-1M tokamak. The main emphasis is placed on the toroidal dispersion of the low-ionised particles just after the injection. The model is realized in a Monte Carlo computer code. Taking into account only two physical processes, namely the diffusion in the momentum space and the ionization of the injected atoms, good agreement with the experimental results can be demonstrated. A new method for the plasma edge electron density determination, using the widths of the toroidal distributions, is also proposed.