Specific Features of the Design and Operation of Magnetic Resonance Mass Spectrometers

Abstract

Magnetic resonance mass spectrometers (MRMSs), developed in the second half of the 20th century at the Ioffe Institute, have still possessed such a complex of parameters that they have no alternative for solving many analytical problems, in particular, in the isotopy of helium. With the resolution of one of the devices several thousand at the base of the 3He+ mass peak, its absolute sensitivity is <106 atoms of this isotope in the volume of the mass analyzer chamber (~2.5 L), and the 3He/4He isotope ratio measured in a single experiment can be as low as 109 and even 1010. Another device of this type demonstrated resolution of more than 150 000 at the base of the mass peak, which ensured the detection of a 3He+–3T+ doublet. Excellent analytical characteristics of the MRMSs make it possible to use them to study the isotopy of helium in natural and man-made samples (solid, liquid, or gaseous) in meteorites and lunar soil, ferromanganese nodules from the bottom of seas and oceans, in ice cores from the well of Lake Vostok in Antarctica, in water from mountain streams of Mongolia and geysers of Iceland, in volcanic gases of Kamchatka and gases released from structural materials of a modern thermonuclear installation. In this work, we consider the principle and modes of operation of an MRMS and its design. The focus is on the details that distinguish these instruments from other instruments and ensure extremely high analytical performance, which is partly presented in the article.