Large-area Si(Li) orthogonal-strip detectors
Segmented lithium drifted silicon detectors are being developed for use in large Compton cameras and for medical imaging. We have successfully fabricated 3.5 mm thick crossed-strip detectors with active areas of 40 /spl times/ 40 mm/sup 2/ with a 2 mm strip pitch. These detectors utilize new contact technology consisting of a boron implanted p-type contact and an amorphous silicon (/spl alpha/-Si) n-type contact. Good energy resolution and excellent strip separation was obtained from both contacts at relatively high operating temperatures. An energy resolution of 2.1 keV FWHM at 122 keV was obtained for the /spl alpha/-Si strip at temperature up to 200 K and for the B strip at temperature up to 240 K. Measurements of the charge sharing between the strips were also performed. When the detector was flood illuminated with 60 keV gamma-rays, a small signal deficit was observed for events in which the signal was shared between two adjacent strips. The amount of deficit depended on the contact type, strip geometry and the operating temperature.
Optimization of the performance of a pixellated germanium Compton camera
A planar HPGe Compton camera for nuclear medicine applications that contains 177 pixels of 4 × 4mm2, of which 25 are at the back detector, is being used to image point sources of Cs137, line sources and clinical-like shape distributed sources. Experimental results are obtained to study the e ffects of energy resolution, position sensitivity, and reconstruction algorithms on camera images. Preamplifi ed pulses are digitized for pulse shape analysis using gamma ray tracking GRT4s data acquisition cards to improve camera performance. Pulse shape analysis includes improving energy resolution of the camera, improving position sensitivity of the camera by using induced charges in neighboring pixels and implementing time coincidence algorithms to select good events. The energy resolution e ffects will be presented for three di fferent energy resolutions at 662 keV; 1.4% by implementing a basic pulse height algorithm, 0.7% with a curve fitting algorithm and 0.3% by implementing the moving window deconvolution algorithm (MWD). By improving the position sensitivity from 2.5mm to 1.25mm, an improvement of 24% in spatial resolution is expected where the currentspatial resolution of a point source 5cm from the camera is 8mm. The results show that the e ects of energy resolution are less important for this camera. Images are reconstructed using back-projection and ITEM (Imaginary Time Expectation Maximization) algorithms. Eff ects of scattering materials on embedded sources are studied. Diff erent source distributions have been studied including point sources, line sources and clinical simulations (baby-heart-like distributed sources).
A self-triggering silicon tracking telescope for spectator proton detection
With the ANKE spectrometer at the COoler SYnchrotron COSY Juelich the mesonic structure of the nucleon will be studied in polarized proton-proton and proton-deuteron collisions. Especially the identification and tracking of low energy protons allows using deuterium as an effective neutron target. For this purpose modular self-triggering tracking telescopes built up by double-sided silicon strip detectors inside the accelerator ultra high vacuum have been developed. Their basic features are E/E proton identification from 2.5-40 MeV and particle tracking over a wide dynamic range, either 2.5 MeV spectator protons or minimum ionizing particles. By the use of self-triggering readout chips the telescopes identify a particle passage within 100 ns and allow therefore the possibility of a fast hit pattern recognition. In combination with a read-out pitch of /spl sim/200 /spl mu/m, they provide a high rate capability. Especially the recent development of very thick (5 mm) double-sided micro structured Si(Li) and very thin (65 /spl mu/m) double-sided Si-detectors provides the use of the telescopes over a wide range of particle energies.