High-performance double-focusing mass spectrometer

A small size double-focusing mass spectrometer employing the Mattauch–Herzog geometry is described. Although developed primarily for helium isotope analyses, the design is such that it can be modified for a wide range of problems. The maximum radius of curvature of ions in the magnetic analyzer is 9.53 cm. With reasonably wide slits 3He can be separated from the HD+H3 combination usually present as an impurity while making analyses of helium in a static mode. At xenon the overlap at adjacent mass numbers is less than 1/10 000. In static operation the sensitivity approaches that of some of the large high sensitivity instruments employing special ion sources. The response is linear over a large pressure range. Since a conventional electron bombardment ion source is employed, ionizing electron energies may be varied, eliminating doubly charged ions such as 40Ar2+ which may interfere with 20Ne analyses. Because of the compact and rugged construction as well as low power consumption, the design lends itself to portable use in field operations.