Abstract: Techniques for calibration of particle detectors are disclosed. In one aspect, a system for calibrating a particle detector includes a source configured to emit particles including a first and a second type of particles; a first and a second shielding unit configured to be removably positioned in a travel path of the particles and configured to block at least a portion of the first type of particles and to allow the second type of particles to traverse substantially unimpeded therethrough; one or more particle detectors positioned in the travel path of the particles to receive particles after traversing through the first or the second shielding unit and produce electronic pulses in response to the detection of the particles; and a processor coupled to the one or more particle detectors to generate training date and a classifier that allows classification of the first and the second types of particles.