14C autoradiography with an energy-sensitive silicon pixel detector

The first performance tests are presented of a carbon-14 (C-14) 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 mu m thick silicon detector with 256 x 256 pixels of 55 mu m 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) x 10(-3) cps mm(-2) kBq(-1) g, background level, (3.59 +/- 0.01) x 10(-5) cps mm(-2), and minimum detectable activity, 0.0077 Bq. The spatial resolution is 76.9 mu m full-width at half-maximum. These figures are compared with several digital imaging detectors for C-14 beta-particle digital autoradiography.