Schematic plot of EK at d = 4.2 mm for K = 0.005 with and without chopping as a function of the unchopped X-ray intensity at 10 keV. The solid and dashed lines express the equation of the continuous and pulsed X-rays, respectively. The pulse duration, tw, was varied from 1 to 40 µs. The dotted line expresses the calculated value of EK assuming that the X-rays at tw = 10 µs are continuous. The time and frequency on the right-hand side indicate the ion-collection time for that EK value and the corresponding frequency.