SPINNING-WIRE DOSIMETRY FOR ION-BEAM ANALYSIS OF MATERIALS

A novel spinning-wire dosimetry system has been developed for the MeV ion beams normally used in ion-beam analyses of materials. The system consists of a spinning wire that crosses the beam axis before the specimen, a surface barrier detector with externally selectable collimating apertures, and a retractable Faraday cup located behind the retractable specimen holder. The surface barrier detector provides energy spectroscopy of the ions backscattered from the spinning wire as it passes through the ion-beam axis. A high-energy segment of the backscattered spectrum is counted in a single-channel analyzer and calibrated against a simultaneous measurement of the integrated beam current using the Faraday cup. For MeV He+ ions with currents of 2-200 nA, the present system has been shown to provide counts that are proportional to the integrated currents with a precision of 1%.