Status of the naval research laboratory trace element accelerator mass spectrometer: Characterization of the Pretzel magnet

A novel design for a trace element accelerator mass spectrometer has been developed at the Naval Research Laboratory and is now under construction. It will allow parallel analysis of a broad range of impurities in electronic, biological, and geological materials. The system includes a modified commercial secondary ion mass spectrometer (Physical Electronics, model 6300) as the source of secondary ions, a recombinator consisting of a Pretzel magnet that serves as a tunable notch mass filter, a 3MV Pelletron tandem accelerator, a large electrostatic analyzer, and a split-pole magnetic spectrograph with a 1.5-m-long focal plane. All other ion optical and steering elements are electrostatic, to maintain parallel transmission of different mass species. This paper summarizes the design concept, and describes in some detail the characteristics of the Pretzel magnet.