The development of an array of cooled large area Si(Li) detectors

Abstract

A system containing six cooled, 34 mm diameter by 7 mm thick, high-resolution Si(Li) detectors designed to maximize the sensitivity for counting X-rays in the 10–30 keV range to measure trace radionuclides in soil samples has been successfully fabricated. The detectors were mounted in a paddle-shaped cryostat with a single large beryllium window on each side. This configuration provides for efficient anticoincidence background suppression and effectively doubles the sensitive detector area because X-rays can impinge on the detectors from both sides. To maximize detection efficiency, the thickness of the cryostat was held to a bare minimum (25 mm); this caused severe difficulties during fabrication of the system. Cutting down the rim of the detectors reduced to an acceptable level the microphony caused by movement of the beryllium window that faces the lithium-diffused contact of the detectors. Since this system will be used for low level counting, careful testing was performed to select materials having the lowest radioactivity.