Zur Messung langer transversaler kernmagnetischer Relaxationszeiten

Abstract

Measurements of long transversal nuclear magnetic relaxation times T₂ exceeding 0.05 — 0.5 sec in low viscosity liquids are performed in most cases with the CARR—PURCELL-method ³, as improved by GILL and MEIBOOM ². The latter furnishes a compensating effect against maladjustments of the pulse lengths t_i in the CARR-PURCELL sequence, brought about by a π/2 phase shift of the radio frequency during the first pulse. This effect is investigated theoretically and experimentally for the second echo of a pulse sequence, where the compensation first occurs. For this purpose the influence of pulse lengths t_i, of the relaxation times T₁ and T₂ and of deviations from resonance Δω is calculated explicitly. The results show that the π/2 phase shift necessary for the GILL-MEIBOOM method can be replaced by a small resonance shift. The effect of radiation damping is demonstrated experimentally.