Apparatus and method for measuring nuclear spin-lattice relaxation time (t1) by tone-burst modulation

Claim 1

Nuclear magnetic resonance apparatus comprising: a transmitting coil and a receiving coil having axes at right angles to each other and intersecting at a point within the confines of each coil; means for supporting a sample to be analyzed substantially at said point of intersection; means for continuously applying radio frequency energy of constant amplitude and frequency to the transmitting coil for subjecting the sample to an alternating radio frequency magnetic field of constant amplitude and frequency directed along the axis of the coil; means for producing in the region of said sample a continuous unidirectional polarizing magnetic field having a direction normal to the plane of said intersecting axes and having a fixed value differing slightly from the value required for nuclear magnetic resonance in said sample at the frequency of said radio frequency field; means operative during the ''''on'''' periods of a series of alternate ''''on'''' and ''''off'''' periods for superimposing on said fixed polarizing field and in alignment therewith a relatively weak additional unidirectional field alternating between maximum and minimum values in accordance with a symmetrical nonrectangular modulating wave the period of which is very much less than the time required for the sample to obtain spin-lattice equilibrium, said additional field being of such magnitude and polarity that the resulting total polarizing field has an alternating component centered on said resonance value; a recorder having a constant velocity sweep for recording the amplitude of a signal as a function of time; means for initiating the start of the recorder sweep at the beginning of each ''''on'''' period; and means coupled to said receiving coil for producing a signal proportional to the amplitude of the voltage induced in the coil by the precessing magnetic moment of the sample and for applying the signal to said recorder.