Performance of position sensitive scintillator detectors when readout with a low noise photodevice
The technique of position sensitive scintillating bar detectors used as the building blocks of position sensitive planes offers the remarkable advantage of greatly reducing the number of readout electronic chains. A position sensitive bar is usually readout by two photo-detectors and, combining the two signals, energy and position of an interacting particle or gamma-ray can be evaluated. In this kind of detector the performances can suffer from the double readout that introduces the noise and uncertainty of two readout systems. The use of Silicon Drift Chamber as a photo-detector opens new perspectives in the design of scintillating bar detectors. In this case the high quantum efficiency of Si for light detection and the very low noise of the device practically cancel the disadvantages of a double readout system. In this work the results achieved stimulating with gamma rays of different energies scintillating bars with square cross section of 3 mm and various length from 15 cm to few cm, with double side Silicon Drift Chamber readout are presented and discussed. For these test an old scintillating material as CsI(Tl) has been chosen manly for its easy availability in different shapes and the good matching of the wavelength of its scintillation light with Si. The use of different materials is also discussed.
Detectors for high-resolution gamma-ray imaging based on a single CsI(Tl) scintillator coupled to an array of silicon drift detectors
Silicon drift detectors (SDDs) coupled to scintillators have been recently employed successfully in gamma-ray detection. The low value of output capacitance of an SDD allows to reach a lower electronics noise with respect to a conventional silicon photodiode. Detectors based on array of SDDs are of particular interest for gamma-ray imaging. A first prototype conceived for high-resolution imaging is based on a monolithic array of small SDDs (5 mm/sup 2/ each unit) with on-chip junction field-effect transistor (JFET). The first results obtained with a seven-elements array are here reported. For the realization of gamma detectors of larger active areas based on assembled units; SDDs of 30 mm/sup 2/ of area with external JFET have been produced. We present the experimental results obtained in the characterization of a single CsI(Tl)-SDD unit.
rPET detectors design and data processing
Small animal PET systems based on rotating planar detectors posses some interesting advantages for high sensitivity, high resolution imaging. We have designed the rPET detectors based on MLS crystals assembled on a 30times30 matrix optically coupled to a flat-panel PS-PMT. Weighted position readout circuits pre-process the 64 signals from the 8times8 anodes matrix, which are digitized using a charge-integrating converter. The amplification electronics, including the trigger output for coincidence detection, and the high voltage supply are integrated in a three PCBs stack that forms the base attached to the back of the PMT. The whole assembly is enclosed in a light tight, lead (Pb) shielded aluminum box. The detectors are mounted on a rotating gantry with more than 180 degrees rotation span. The digitized events are screened and histogramed, and a modified center of gravity algorithm removes from the position calculation those signals with poor signal to noise ratio. Apparent mean crystal size on the 511 keV field-flood images is 0.6 mm, mean peak-to-valley ratio is better than 8, and intrinsic resolution is 1.5 mm at the central row, with the energy window wide open. Sensitivity (CPS) for a pair of these detectors set in coincidence at 160 mm distance is 1%