Calculations of the average electronic stopping power S, for heavy ions in solids are performed within the framework of the modified Firsov theory. Consideration is given to the effect of the usual approximations of straight line trajectories, free-atom electron densities, and the positioning of the dividing surface between the atoms a t a fixed fraction of their separation. When He is averaged over all impact parameters, for classical orbits, the variation of S, as a function of target atomic number 2, is much smaller than the variation previously determined by other authors for forward-scattered particles. The use of a simple approximation for the electron densities in solids, in conjunction with a Thomas-Fermi estimate of their velocities during the interaction, leads to results that are very similar to the free-atom case.Nous avons procede B des calculs du pouvoir d'arrbt electronique moyen dans le cas d'ions lourds dans un solide dans le contexte de la theorie de Firsov modifih. Nous avons pris en consideration les effets des approximations usuelles des trajectoires en ligne droite, des densites electroniques basbes sur le modde de l'atome libre et de l'effet de la position de la surface sbparant les atomes comme se trouvant A une fraction de leur sbparation.Lorsqu'on fait la moyenne de He Bur tous les parametres d'impact, dans le cas d'orbites classiques, la variation de 8, en fonction de Z,, le nombre atomique de la cible, est de beancoup infbrieure A celle determinee prbcbdemment par d'autres auteurs dans le cas de particules diffusbes vers I'avant. Nous montrons qu'une simple approximation des densites electroniques dans les solides, en conjonction avec une estimation de leur vitesse durant l'interaction utilisant le modhle de Thomas-Fermi, conduit it des resultats qui s'avhrent tr&s similaires A ceux obtenus dans le cas du mod6le d'un atome libre.
IntroductionThe Firsov theory [ 13 for the electronic stopping cross-sections of low-velocity heavy ions has been modified by various authors [Z to 51 to account for oscillatory structure in the electronic stopping cross-section S , as a function of the atomic number of both the projectile 2 , [6 to 131 and target 2 , [ 14 to 201. Since the experimentally observed oscillations have generally been for either forwardscattered particles or for channeled particles, the theoretical calculations have approximated the trajectories of the incident particles by straight lines (impulse approximation). This approximation is valid in cases where close encounters do not contribute to the phenomena being observed.In some experiments, however, the energy loss averaged over all impact parameters is required. Such is the case, for example, in the measurement of nuclear decay lifetimes by the Doppler shift attenuation method (DSAM). In this method an excited nucleus moves in an energy absorbing medium and the energy of the emitted gamma radiation is Doppler shifted in a manner that depends both on the lifetime of the state and the stopping power of the medium.
Broude et al. [21...
