Fig. 7.

Measured average signal per electron as a function of incident electron energy for TVIPS 224 CCD $(■)$, SO-163 film $(•)$, MAPS $(♦)$ detector. The results have been arbitrarily scaled to have a peak value of $\sim 100$. The lines through the data points are simply aids to the eye. The shape of the response curve is similar for all three detectors. Extrapolating to zero response gives threshold energies of 5, 8 and 24 keV for the CCD, film and MAPS detectors, respectively.