A particle-counting apparatus is described, which reduces a resulting width of pulses when a charge pulse is received from a particle detector, thereby reducing pile-up problems with pulses. Pulse shortening is obtained by resetting the pulse shortly after it exceeds its peak level at the apparatus output. The apparatus includes a charge-sensitive amplifier and a shaper which generates an output for subsequent discrimination circuits. A reset generator monitors the shaper output and generates a reset signal to the shaper when a peak has been detected.