An ISPA camera for beta radiography

We have developed a new type of beta camera based on an imaging silicon pixel array (ISPA) tube combined with planar plastic scintillators or with SiY₂O₅:Ce scintillating powder. The ISPA tube consists of a photocathode viewed at 3 cm distance by a silicon anode divided into 1024 rectangular (75 μm×500 μm) detector pixels, each bump-bonded to its equally sized electronic pixel. Depending on the beta detector thickness we achieved spatial resolutions (FWHM) between 105-μm (⁶³Ni source and 30-μm-thick plastic scintillator) and 240-μm (⁹⁰Sr-⁹⁰Y source and 120-μm-thick plastic scintillator) by covering the detectors with brass templates. With their four 60-μm-wide slits oriented parallel to the long pixel edges, we simulated small-sized beta strips. The impact of detector thickness is explained by multiple scattering, angular aperture of the template slits, and scintillating light distribution at the ISPA photocathode. Beta detection sensitivities were measured with calibrated ³H (tritium)- and ¹⁴C-Amersham microscale sources. They amount to 0.1 Bq (³H) with 150 min counting time and to 0.025 Bq ( ¹⁴C) with 180 min counting time