PNNL

Abstract

Extending pulsed-field-gradient (PFG) NMR diffusometry to nonroutine nuclei requires distinguishing apparent free-induction decay from the refocusable coherence available during echo-based diffusion experiments. Here, concentrated aqueous AgNO3 is used to evaluate relaxation constraints governing direct-observe ¹°?Ag PFG NMR diffusometry. ¹°?Ag exhibits slow longitudinal relaxation (T1 ˜ 600 s), making experimental throughput a practical limitation, and a short apparent transverse decay (T2* = 0.1 s), which could suggest restricted diffusion-encoding feasibility. Hahn-echo measurements show that much of this apparent dephasing is refocusable, and Carr-Purcell-Meiboom-Gill measurements quantify the longer refocused transverse relaxation time (T2,CPMG = 60 s). These results show that ¹°?Ag diffusion NMR feasibility cannot be assessed from the one-pulse linewidth alone, but must also account for experimentally demonstrated refocusable coherence. Direct-observe ¹°?Ag PFG NMR was feasible using modest gradient strength (