Development of a detector based on Silicon Drift Detectors for gamma-ray spectroscopy and imaging applications

Abstract

This work deals with the development of a new gammadetector based on Silicon Drift Detectors (SDDs) to readout largeLaBr3:Ce scintillators for gamma-ray spectroscopy and imagingapplications. The research is supported by the European Space Agency throughthe Technology Research Programme (TRP) and by Istituto Nazionale di FisicaNucleare (INFN) within the Gamma project. The SDDs, produced at FondazioneBruno Kessler (FBK) semiconductor laboratories, are designed as monolithicarrays of 3 × 3 units, each one of an active area of 8 mm × 8 mm (overall area of 26 mm × 26 mm). The readout electronics and thearchitecture of the camera are briefly described and then first experimentalresults coupling the SDD array with a 1'' × 1'' LaBr3:Cescintillator are reported. An energy resolution of 3% FWHM at 662 keV hasbeen measured at -20°C, better than coupling the same scintillator witha photomultiplier tube. The same scintillator is also used to evaluateposition sensitivity with a 1 mm collimated Cs-137 source. The maindifficulty in determining the position of the gamma-ray interaction in thecrystal is associated to the high thickness/diameter ratio of the crystal(1:1) and the use of reflectors on all lateral and top sides the crystal.This last choice enhances energy resolution but makes imaging capabilitymore challenging because light is spread over all photodetectors.Preliminary results show that the camera is able to detect shifts in themeasured signals, when the source is moved with steps of 5 mm. A modifiedversion of the centroid method is finally implemented to evaluate theimaging capability of the system.