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 microm x 500 microm) detector pixels, each bump-bonded to its equally-sized electronic pixel. Depending on the beta-detector thickness we achieved spatial resolutions (FWHM) between 105 microm (63Ni source and 30 microm thick plastic scintillator) and 240 microm (90Sr-90Y source and 120 microm thick plastic scintillator) by covering the detectors with brass templates. With their four 60 microm 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.