A system for calibrating a radiation detector, comprising: a source configured to emit particles or rays including a first type of particles or rays and a second type of particles or rays; a first and a second shielding unit, the first shielding unit configured to be removably positioned at a first distance from the source in a travel path of the particles or rays that are emitted from the source and the second shielding unit configured to be removably positioned, after the first shielding unit, along the travel path of the particles or rays at a second distance from the source, each shielding unit configured to block at least a portion of the first type of particles or rays and to allow the second type of particles or rays to traverse substantially unimpeded therethrough; one or more detectors positioned in the travel path of the particles or rays to receive one or more particles or rays, wherein the one or more detectors are configured to detect the first type of particles or rays and the second type of particles or rays and to produce electronic pulses in response to the detection of the first and the second type of particles or rays; and a processor coupled to the one or more detectors, the processor further coupled to a memory including instructions executable by the processor, the instructions executable by the processor to configure the processor to receive a first set of pulses from the one or more detectors corresponding to detections with the first and the second shielding units configured to be in place, a second set of pulses from the one or more detectors corresponding to detections with the first shielding unit configured to be in place and with the second shielding unit configured to be removed, and a third set of pulses from the one or more detectors corresponding to detections with both the first and the second shielding units configured to be removed, the processor further configured to store at least a first set of training pulses corresponding to the first type of particles or rays and a second set of training pulses corresponding to the second type of particles or rays, and to generate a classifier that allows classification of the first and the second types of particles or rays. a source configured to emit particles or rays including a first type of particles or rays and a second type of particles or rays; a first and a second shielding unit, the first shielding unit configured to be removably positioned at a first distance from the source in a travel path of the particles or rays that are emitted from the source and the second shielding unit configured to be removably positioned, after the first shielding unit, along the travel path of the particles or rays at a second distance from the source, each shielding unit configured to block at least a portion of the first type of particles or rays and to allow the second type of particles or rays to traverse substantially unimpeded therethrough; one or more detectors positioned in the travel path of the particles or rays to receive one or more particles or rays, wherein the one or more detectors are configured to detect the first type of particles or rays and the second type of particles or rays and to produce electronic pulses in response to the detection of the first and the second type of particles or rays; and a processor coupled to the one or more detectors, the processor further coupled to a memory including instructions executable by the processor, the instructions executable by the processor to configure the processor to receive a first set of pulses from the one or more detectors corresponding to detections with the first and the second shielding units configured to be in place, a second set of pulses from the one or more detectors corresponding to detections with the first shielding unit configured to be in place and with the second shielding unit configured to be removed, and a third set of pulses from the one or more detectors corresponding to detections with both the first and the second shielding units configured to be removed, the processor further configured to store at least a first set of training pulses corresponding to the first type of particles or rays and a second set of training pulses corresponding to the second type of particles or rays, and to generate a classifier that allows classification of the first and the second types of particles or rays.