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.
Large-volume Si(Li) orthogonal-strip detectors for Compton effect based instruments
Recent developments of large-area Si(Li) orthogonal-strip detectors have revealed their capability for applications in Compton effect based instruments. Some inherent advantages of silicon like dominance of Compton scattering in photon interactions and operation at room or somewhat lower temperature combined with the availability of large-volume Si(Li) detectors could stimulate the development of powerful Compton instruments. Several 10 and 20 mm thick diodes with a diameter of 102 mm were fabricated. Two 10 mm thick diodes were cut to form a 74 mm /spl times/ 74 mm square with slightly rounded corners. The same position-sensitive structure, 32 strips with a pitch of 2 mm, was produced on the thin Li-diffused n-contact and boron implanted p/sup +/-contact by means of photolithography and plasma etched grooves. The position-sensitive area of 64 mm /spl times/ 64 mm is surrounded by a 5 mm wide guard-ring. One of these 10 mm thick Si(Li) orthogonal-strip detectors will be mounted in a cryostat prepared at LLNL. There, the detector will be extensively tested with the goal to be integrated into the compact Compton camera system consisting of double-sided strip Si(Li) and HPGe detectors.
Long Ceramic Beam Tubes for Accelerator Magnets
The ceramic beam tubes for the fast and abort kickers and the bucker and pinger magnets used at Fermilab must meet a number of exacting requirements. The tubes must be long and sufficiently straight so as not to limit magnet design. They must have wall strength capable of withstanding the atmospheric and mechanical forces encountered during construction and operation. Vacuum tight ceramic to stainless steel transitions must be of reasonable cost; they must also withstand high temperature processing and remain vacuum tight to the 10/sup -9/ Torr range. To remove the possibility of static charge buildup each tube must have a surface coating of indium oxide applied to the inner wall. This thin coating is difficult to achieve and requires the most careful attention to detail. The methods used at Fermilab to achieve these goals are presented in this paper.