Particle emission induced by ionization tracks in water ice

We study electron emission and sputtering during irradiation of amorphous water ice at 60 K by H+, D+, He+, Li+, Be+, B+, C+, N+, O+, F+, and Ne+ ions in the energy range from 10 to 100 keV. We find that for constant velocity (5 keV/amu) ions the dependence of the sputtering yields with projectile atomic number Z is proportional to the square of the Z-dependence of the electronic stopping power dE/dx, using dE/dx values predicted by Yarlagadda, Robinson, and Brandt. The electron yields increase sublinearly with dE/dx, indicating the strong influence of un-neutralized holes in the ionization track produced by the projectiles. (orig.)