The invention provides a method of estimating an input count rate of a radiation pulse detector from a detector signal where some individual signal pulses making up the detector signal are closely spaced in time less than a minimum reliable detection gap. In one aspect, the individual signal pulses are detected using a detection algorithm and a plurality of interval start times are defined each interposed with at least one of the detected individual signal pulse arrival times, each interval start time being later by at least the minimum reliable detection gap than a corresponding most recent detected individual signal pulse arrival time. A corresponding plurality of individual signal pulse arrival intervals are calculated between each of the interval start times and a corresponding next detected individual signal pulse arrival time.