AN EARTHS FIELD NUCLEAR-MAGNETIC-RESONANCE APPARATUS SUITABLE FOR PULSED GRADIENT SPIN-ECHO MEASUREMENTS OF SELF-DIFFUSION UNDER ANTARCTIC CONDITIONS

We describe an earth's field nuclear magnetic resonance apparatus whic h can be used to carry out pulsed gradient spin echo (PGSE) diffusion measurements. The instrument is portable and incorporates automated pr ocess control, allowing direct measurement of the Larmor precession. T he use of a common clock for pulse sequencing, excitation pulse synthe sis, and detection, results in a phase stability sufficient for accura te signal averaging. The analysis of PGSE data under the conditions of a weak detection field is discussed and measurements of diffusion are presented under both New Zealand and Antarctic conditions. The Antarc tic results include an example of restricted diffusion of brine water in McMurdo Sound sea ice. (C) 1997 American Institute of Physics. [S00 34-6748(97)04311-6].