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.
Development of double-sided microstructured Si(Li)-detectors
A new technique for manufacturing double-sided structured Si(Li)-detectors has been established. The position-sensitive structure on the implanted p/sup +/-contact can be realized, even finer than 100 /spl mu/m, by means of photolithography and plasma-etching of grooves, which then separate the position elements. By modifying this technique position-sensitive structures on thin (/spl sim/30 pm) Li-diffused contact were performed. Areas of 50 mm /spl times/50 nm were divided into 50 or 100 strips with a pitch of 1 mm or 500 /spl mu/m respectively. The strips were separated by /spl sim/35 /spl mu/m deep and /spl sim/50 /spl mu/m wide grooves. Measurement of electrical resistance of the grooves and the reverse current of the strips are presented. Charge splitting on the adjacent strips shows practically no charge loss through the groove. Small pixel effects are demonstrated on a Li-diffused contact (100 strips with the pitch of 500 /spl mu/m) and on the first double-sided Si(Li)-detector (50/spl times/50 strips with the pitch of 1 mm). The capability of 3D-imaging for such detectors is proven.
A Multi-Element Silicon Detector for X-Ray Flux Measurements
A 30-element Si(Li) detector has been fabricated to measure the one-dimensional flux profile of 33 KeV x-rays from a synchrotron radiation beam. The device, which is fabricated from a single 39mm × 15mm silicon wafer, is a linear array of 0.9mm × 7mm elements with a 1mm center-to-center spacing. It is 5mm thick and when operated at room temperature has an average leakage current of 10 nA/element. The x-ray flux in each element is determined by measuring the current with a high quality operational amplifier followed by a current digitizer. This detector is being used to study the use of synchrotron radiation for non-invasive imaging of coronary arteries. The experiment uses the difference in the transmitted flux of a monochromatized x-ray beam above and below the iodine K-edge. Measurements have been made on plastic phantoms and on excised animal hearts with iodinated arteries. The images obtained indicate that a 256-element device with similar properties, but with 0.6mm element spacing, will make a very effective detector for high-speed medical imaging.