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 SiY/sub 2/O/sub 5/:Ce scintillating powder. The ISPA tube consists of a photocathode viewed at 3 cm distance by a silicon anode divided into 1024 rectangular (75 /spl mu/m/spl times/500 /spl mu/m) detector pixels, each bump-bonded to its equally sized electronic pixel. Depending on the beta detector thickness we achieved spatial resolutions (FWHM) between 105-/spl mu/m (/sup 63/Ni source and 30-/spl mu/m-thick plastic scintillator) and 240-/spl mu/m (/sup 90/Sr-/sup 90/Y source and 120-/spl mu/m-thick plastic scintillator) by covering the detectors with brass templates. With their four 60-/spl mu/m-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 /sup 3/H (tritium)- and /sup 14/C-Amersham microscale sources. They amount to 0.1 Bq (/sup 3/H) with 150 min counting time and to 0.025 Bq (/sup 14/C) with 180 min counting time.