Two-frequency method for increasing the signal-to-noise ratio for nuclear quadrupole resonance14N low-frequency transitions

A method is proposed for increasing the signal-to-noise ratio during detection of NQR¹⁴N low-frequency transitions, consisting in a preliminary saturation of the _o(_–) transition before accumulation of the multiplet signals of the spin echo or induction signals, observed during the action of a series of 90 pulses on the _–(_o) transition. The gain in signal-to-noise ratio achieved by the two-frequency action is calculated theoretically, and the maximum value is found to be 3/(3 –) for _– and 3(1 + )/4 for _o. It is shown that the envelope of the induction signal for an increase in the time between the 90 pulses decreases according to one exponent for _o, while for _– and ₊ it decreases according to two exponents, and the approach to equilibrium of the system of¹⁴N nuclei is oscillatory in nature.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 61–64, November, 1987.