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.
Thermally Induced Dynamics of Satellite Solar Panels
Thermally induced structural motions are known to affect the attitude dynamics of low Earth orbiting satellites during eclipse transitions. Motions of e exible appendages such as solar panels lead to rigid body rotations of the entire satellite because the total angular momentum of the system is conserved. These potentially large attitude disturbances may violate pointing accuracy and jitter requirements. One type of thermally induced dynamics exhibited by solar panels is thermal snap. The Upper Atmosphere Research Satellite is a prominent example of a satellite that experiences thermal snap disturbances during eclipse transitions. This paper describes recent studies of thermally induced dynamicsof solarpanels, including an analysisofsatelliteattitudedynamics resulting from thermally induced structural motions and a laboratory investigation of the thermal-structural performance of a satellite solar panel. Analytical and experimental results demonstrate thermal bending deformations with acceleration transients that have characteristic thermal snap disturbance histories in response to rapid changes in heating. The studies show that solar panel thermal snap disturbances are caused by through-the-thickness temperature differences that vary at a nonconstant rate. Finite element analysis correctly predicts the thermal snap phenomenon observed in the solar panel experiments.