Large area silicon drift detectors for new applications in nuclear medicine imaging

In this work we have investigated the performance of a large area (1 cm²) square shaped Silicon Drift Detector (SDD) operating as a gamma-ray detector in direct conversion mode as well as a photodetector in combination with a single crystal CsI:Tl scintillator (10 mm × 10 mm × 7 mm). An external FET along with a low-noise charge sensitive preamplifier was used for testing the prototype detector in the temperature range -23°C to 26°C. In direct conversion mode the SDD exhibited an energy resolution of 195 eV FWHM (at 5.9 keV, -23°C, 4 μs shaping time). Pulse height spectra and signal rise times were recorded at different locations across the SDD surface with the aid of a relocatable collimator. Depending on collimator position we measured signal rise times between 100 ns and 750 ns. After coupling the CsI-scintillator directly to the SDD surface we obtained an excellent energy resolution of 7% FWHM with an uncollimated ⁵⁷Co source (122 keV, -10°C, 12 μs shaping time). The corresponding signal rise time was approx. 20 μs. A short analysis regarding the different SDD-signal rise times with and without scintillator will be presented.