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 small est thermal equilibrium populations, in the m = +/- I levels, are tran sferred to the m = +/- 1/2 levels. The resulting signal enhancement of the central transition is of maximum value 2I. The population transfe r is accomplished by frequency or field sweeping, resulting in sequent ial adiabatic inversions of the satellite transitions. Thus, the techn ique works on powder and amorphous samples as well as on single crysta ls, as demonstrated in experiments on Al-27 in Al2O3.