A one-dimensional particle-in-cell code has been used to study the barium release experiment CRIT II. The electrodynamic response of the ionosphere to these injections has been modeled by magnetic-field-aligned currents, using the concept of Alfv¿n conductivity. After the active phase, when the fast part of the neutral barium cloud passed the payload, the particle detector 5AB in the CRIT II experiment, aimed almost perpendicular to the ambient magnetic field B in the direction toward the release, showed two clearly defined types of peaks having different durations, frequencies, and energy distributions. This particle energy spectrum has been reproduced in the numerical simulations. It is shown that geometrical effects and phase shifts of the ions are of secondary importance for the creation of the double-peaked structure. A qualitative model, based on the selective acceleration of barium ions due to electric fields set up by the injection process, is developed to explain the observations. ¿ American Geophysical Union 1993