Additionally, the mean intensity I0 of the interference pattern on the detector was determined for hydrogen with increasing pressure. It represents the center line of the cosine-function in Eq. (1). The data is plotted in Fig. 4. As expected, a significant signal drop is determined. This is presumably due to increasing collisions between electrons and H2 molecules that decrease the count rate. At a pressure of 9:3 105 mbar only a fraction of 6% of the original electron signal is left.