Homonuclear Dipolar Coupling and CPMG Spin-Echoes in NQR

The nuclear quadrupole resonance signals from both a single crystal and a powder sample of spin-1 nuclei under a Carr–Purcell–Meiboom–Gill are modeled numerically. While the single crystal clearly shows the effects of dipolar coupling for on-resonant pulses, the powder does not. However, for certain off-resonant conditions, the powder sample exhibits the same response as the single crystal. Experimentally, this corresponds to the observation of a rapid decay at these conditions. Using a powder sample of NaNO 2 , the functional form of the echo train, when the dipolar coupling is not refocused, is clearly different than the decay for an on-resonance sequence, and can be used to characterize the dipolar coupling.