Experiments have been performed to measure the effect of Cs gamma emission on the length and distribution of long chains of C02 laser-induced plasma beads in atmospheric pressure air. Schlieren photography data show that negative ions produced by the Cs source result in a shift of the breakdown plasma to lower C02 laser intensity regions. No significant change in the total plasma length or uniformity has been observed. These experiments are relevant to the role of wall activation in fusion reactors using electron or light ion beams injected through plasma channels.