A method of detecting a pileup in an energy-dispersive radiation spectrometry system, wherein a filter of the system generates a first pulse in response to a preamplifier signal, and wherein the system has one or more fast channels having an energy of full efficiency wherein substantially all photons received having at least the full efficiency energy are detected. The method includes measuring an above threshold time duration of the filter, determining that the fast channels have not made any detections while the first pulse is above the minimum detectable threshold energy of the filter, in response thereto, declaring a pileup if the above threshold time duration exceeds a longest expected pulse duration that is a duration of a second pulse that would be output by the filter in response to a single photon having an energy equal to the energy of full efficiency being received by the system.