Pulse counting detectors provide the ultimate in measurement sensitivity, because individual radiation interactions can be measured. Examples include photomultiplier/scintillators, continuous dynode electron multipliers, channel plates, avalanche photodiodes and silicon photomultipliers. The C400 and associated CP10 pre-amplifiers are designed to count the pulses from such detectors up to high rates, typical of the latest scintillator materials and solid state sensors. The D100 is a pulse shape analysis tool that allows you to do spectroscopy with detectors that discriminate the energy of the incoming radiation.