SENSITIVITY ENHANCEMENT FOR NMR OF THE CENTRAL TRANSITION OF QUADRUPOLAR NUCLEI

A sensitivity enhancement technique for the central transition of half-integer nuclear spins is reported. For a spin-I the largest and smallest thermal equilibrium populations, in the m = +/- I levels, are transferred to the m = +/- 1/2 levels. The resulting signal enhancement of the central transition is of maximum value 2I. The population transfer is accomplished by frequency or field sweeping, resulting in sequential adiabatic inversions of the satellite transitions. Thus, the technique works on powder and amorphous samples as well as on single crystals, as demonstrated in experiments on Al-27 in Al2O3.