Digital autoradiography with a Medipix2 hybrid silicon pixel detector

A digital imaging system for beta and gamma autoradiography has been realized. It is a hybrid pixel detector based on a Medipix2 circuit (a single photon counting chip), developed at CERN in the framework of the Medipix2 European collaboration, as a successor of the Medipix1 chip. Medipix2 is realized in 0.25-μm CMOS technology; it has a sensitive area of 14 × 14 mm² and a pixel pitch of 55-μm and is bump bonded to a 300-μm-thick silicon pixel detector. A test of this imaging system for digital autoradiography, with a detection threshold of about 6 keV, shows a noise in the order of 10^-3 cps/mm², a minimum detectable activity of 0.32 Bq in 14 h for ³H, and 0.012 Bq in 10 h for ¹⁴C. A preliminary spatial resolution test for ¹⁴C gives a full-width at half-maximum resolution of about 80 μm. Real-time images of ³H, ¹⁴C, ¹²⁵I autoradiographic microscales are shown, and a comparison with existing experimental devices is presented.