FUNDAMENTALS OF PULSED NITROGEN-14 QUADRUPOLERESONANCE

摘要

The essential features of nitrogen-l4 Nuclear Quadrupole Reson-ance, a new tool based on density matrix calculations is proposed. After abrief review of the density matrix theory, it is demonstrated that, for each ofthe three NQR transitions, the (3,3) density matrix can be reduced to a (2,2)matrix, evidently easier to handle. (2,2) rotation matrices are defined forpredicting, in a straightforward manner, the system evolution under a rfpulse. The first example treated by this methodology concerns nutationexperiments (evolution of the signal amplitude as a function of the pulselength) and it is shown that the NMR (Nuclear Magnetic Resonance) flipangle, in the case of powder samples, should be substituted by a pseudo flipangle which is no longer proportional to the pulse length. Still for powdersamples, it is demonstrated that, in NQR, data averaging continuouslyimproves when shortening the repetition time. Finally it has been possibleto define proper phase cycles in view of measuring relaxation times (T1 andT2) by a two-pulse sequence. In all cases, experimental verifications wereperformed in order to assess this methodology.