Digital autoradiography with a Medipix2 hybrid silicon pixel detector

A new digital imaging system for beta and gamma autoradiography has been realized. The technological advancement of this imaging system is represented by the second-generation Medipix2 chip (a single photon/particle 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, it has been bump-bonded to a 300 μm thick silicon pixel detector. A dedicated electronic interface and a complete image acquisition and processing software allow to operate this hybrid pixel detector for digital autoradiography with acquisition time as long as several days. In a preliminary test of this imaging system for digital autoradiography we obtained a detection threshold of 1600 electrons (equivalent to about 6 keV in Si), a noise 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 FWHM resolution of 30 μm. Real time images of ³H, ¹⁴C, ¹²⁵I autoradiographic microscales are also presented.