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14C autoradiography with an energy-sensitive silicon pixel detector

The first performance tests are presented of a carbon-14 (14C) beta-particle digital autoradiography system with an energy-sensitive hybrid silicon pixel detector based on the Timepix readout circuit. Timepix was developed by the Medipix2 Collaboration and it is similar to the photon-counting Medipix2 circuit, except for an added time-based synchronization logic which allows derivation of energy information from the time-over-threshold signal. This feature permits direct energy measurements in each pixel of the detector array. Timepix is bump-bonded to a 300 µm thick silicon detector with 256 × 256 pixels of 55 µm pitch. Since an energetic beta-particle could release its kinetic energy in more than one detector pixel as it slows down in the semiconductor detector, an off-line image analysis procedure was adopted in which the single-particle cluster of hit pixels is recognized; its total energy is calculated and the position of interaction on the detector surface is attributed to the centre of the charge cluster. Measurements reported are detector sensitivity, (4.11 ± 0.03) × 10−3 cps mm−2 kBq−1 g, background level, (3.59 ± 0.01) × 10−5 cps mm−2, and minimum detectable activity, 0.0077 Bq. The spatial resolution is 76.9 µm full-width at half-maximum. These figures are compared with several digital imaging detectors for 14C beta-particle digital autoradiography.