A NEW ACCELERATOR MASS-SPECTROMETER FOR TRACE-ELEMENT ANALYSIS AT THENAVAL-RESEARCH-LABORATORY

A new accelerator mass spectrometer (AMS) facility is under constructi on at the Naval Research Laboratory for trace element analysis of elec tronic, biological, and geological materials. The design provides for parallel mass analysis over a broad mass range for conducting and insu lating samples, and offers 10 mu m lateral image resolution, depth pro filing, and sensitivity down to tens of ppt of trace impurities. The f acility will use a modified commercial secondary ion mass spectrometer as the source of secondary ions. A Pretzel magnet will act as a uniqu e recombinator to simultaneously transmit from 1 to 200 amu ions, but attenuate intense matrix-related beams, After acceleration, a single c harge state will be selected by a 3 degrees electrostatic bend, then t he selected ions will be energy analyzed by a 2.2 m radius, 30 degrees spherical electrostatic analyzer (E/Delta E approximate to 800). Fina lly, a split pole mass spectrograph with a 1.5 m long focal plane will provide parallel analysis over a broad mass range (M(max)/M(min) appr oximate to 8) with high mass resolution (M/Delta M approximate to 2500 ).