Pattern recognition of tracks induced by individual quanta of ionizing radiation in Medipix2 silicon detector

Medipix2 is a semiconductor pixel detector (256×256 pixels, 55×55 μm2 each) which can count individual quanta of radiation. The detector will respond differently for different types of radiation. If the acquisition time is short enough with respect to radiation intensity, one can see characteristic tracks of individual quanta in an image taken (e.g., curved lines for electrons, round shaped clusters for alpha particles, heavy ions and slow neutrons, cone shapes for fast neutrons, simple dots for low energy X-rays, etc.). For effective visualization of neutrons, the device has to be equipped by corresponding neutron converter, which converts neutrons to heavy charged particles. By analyzing these patterns, in this so-called “tracking mode” of operation, it is possible to distinguish individual tracks and classify them into predefined categories. For each “cluster” detected, the features (such as parameters describing the shape and energy deposition estimation) can be extracted and used to distinguish radiation type. The energy deposited can be estimated by using calibration measurements with different types of radiation and variation of the discrimination threshold.