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 spec imen, a surface barrier detector with externally selectable collimatin g apertures, and a retractable Faraday cup located behind the retracta ble specimen holder. The surface barrier detector provides energy spec troscopy 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 again st 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 i ntegrated currents with a precision of 1%.