RU2086965C1 - Method of determination of gyromagnetic relation of nuclei - Google Patents

Abstract

FIELD: study of structure of chemical compounds. SUBSTANCE: method includes acting on specimen of two HF pulses with time interval τ from beginning of cycle to beginning of the second pulse, setting of normal excitation conditions and registration of spin echo, calibrated measurement of value of HF field by the known specimen and determination of gyromagnetic relation of nuclei of tested sample. First pulse width is smoothly varied together with time interval for same value, modulation of echo signal is registered, frequency w₁ is found by maxima of echo signals, and gyromagnetic relation of nuclei is determined as relation between this frequency ω₁ and value of calibrating multifrequency field H₁. EFFECT: higher efficiency. 2 dwg

Description

 The invention relates to radio spectroscopy and can be used to study the structure and structure of chemical compounds.

A known method for determining the gyromagnetic ratio of nuclei, comprising exposing the sample to an adjustable constant magnetic field with known parameters and a radio frequency field, the relationship between which is selected from the conditions of magnetic resonance in the sample, measuring the signal frequency and determining the gyromagnetic ratio of the nuclei as the ratio of the signal frequency to the constant magnetic field [1]
The disadvantages of this method are the complexity and low accuracy, which are mainly due to the complexity of accurate calibration of a constant magnetic field of large magnitude.

There is also a method for determining the gyromagnetic ratio of nuclei, which includes exposing a sample to two radio frequency pulses with a time interval τ from the beginning of the cycle to the beginning of the second pulse, establishing optimal conditions for the excitation and registration of the spin echo signal, calibrating the measurement of the radio frequency field from a known sample, and determining the gyromagnetic ratio of the nuclei test sample [2]
The disadvantage of this method is the low accuracy. This is especially true in the case of NQR, where the 90-degree condition is not always fulfilled.

 The objective of the invention is to develop a simple method for determining the gyromagnetic ratio of nuclei with high accuracy.

This problem is solved using the essential features specified in the claims: common with the prototype method for determining the gyromagnetic ratio of nuclei, including exposure to the sample with two radio frequency pulses with a time interval t from the beginning of the cycle to the beginning of the second pulse, establishing optimal conditions for the excitation and registration of the spin echo signal , calibration measurement of the magnitude of the radio frequency field from a known sample and determination of the gyromagnetic ratio of the nuclei of the test sample and the distinctive closest analogue essential characteristics gradually change the duration of the first pulse and the time interval t at the same value record modulation of the echo signal amplitude, the maxima of which are frequency w ₁ and determining the gyromagnetic ratio of the nuclei as the ratio of the frequency ω ₁ to the value of the calibration radio frequency field H ₁ .

 The following discloses the existence of a causal relationship between the totality of the essential features of the invention and the achieved result.

 First, for the first time, other conditions are used in solving this problem: a smooth change in the duration of the first pulse and the time interval τ by the same value.

Secondly, the modulation of the amplitude of the echo signal is recorded, at the maxima of which the frequency w _{1 is found} .

Thirdly, the gyromagnetic ratio of the nuclei of the test sample is determined as the ratio of the frequency ω ₁ to the value of the radio frequency field H ₁ .

 An analysis of all the distinguishing features of the invention showed that the inventive step was high before such techniques were not used to solve such a problem.

In FIG. 1 shows a pulse program for exciting and recording the amplitude of a spin echo signal; figure 2 the dependence of the amplitude of the echo signal from the duration of the first pulse in KReO ₄ (resonance ¹⁸⁷ Re, J 5/2, transition 3/2 5/2, ν 53.656 MHz, T 296 K).

 The method is implemented using the device described in A.S. N 1132207, CL G 01 N 24/10, 1984.

An example implementation of the proposed method. The optimal conditions for the excitation and registration of the spin echo signal are preliminarily established. The conditions should be as follows: the first RF pulse is 90 ^o , and the second 180 ^o and the time interval t is set so that it is possible to observe the spin echo signal with a large S / N ratio.

Initially, we select a sample that contains nuclei with a known gyromagnetic ratio g. This is necessary to measure the magnitude of the radio frequency field H ₁ , i.e. to calibrate the field. This field value can be previously measured as in the prototype H ₁ = π / 2γt ₁ (from the condition of 90 degrees). It can also be measured as in the invention: from a known sample from the modulation picture, determine ω ₁ and find the magnitude of the radio frequency field H ₁ . In the second case, the accuracy of the measurement of H ₁ will be better at least twice.

где ν₁ частота модуляции;
Т период модуляции.After that, we put the test sample into the sensor and set the optimal conditions for the excitation and registration of the spin echo signal in the calibration radio frequency field H ₁ . After that, the duration of the first pulse and the time interval τ from the beginning of the cycle to the beginning of the second pulse are gradually changed by the same value. In this case, the amplitude of the echo signal is recorded: a modulation of the amplitude of the echo signal will be observed. By the maxima of the signal amplitude we find

where ν ₁ modulation frequency;
T period of modulation.

Чем больше регистрируется модуляционных максимумов, тем точнее измерение T, соответственно точнее определяется гиромагнитное отношение ядер исследуемого образца.Based on this measurement of ω ₁ we find the gyromagnetic ratio of the nuclei of the test sample

The more modulation maxima are recorded, the more accurate is the measurement of T; accordingly, the gyromagnetic ratio of the nuclei of the test sample is more accurately determined.

 Thus, the proposed method for determining the gyromagnetic ratio of nuclei is simple and can improve accuracy at least twice.

Claims (1)

A method for determining the gyromagnetic ratio of nuclei, including exposing a sample to two radio frequency pulses with a time interval τ from the beginning of the cycle to the beginning of the second pulse, establishing optimal conditions for the excitation and recording of the spin echo signal, calibrating the measurement of the radio frequency field from a known sample, and determining the gyromagnetic ratio of the nuclei of the test sample , characterized in that the duration of the first pulse and the time interval t are smoothly changed by the same amount, register cosiness is the modulation of the amplitude of the echo signal, by the maxima of which the frequency w _{1 is found} and the gyromagnetic ratio of the nuclei is determined as the ratio of this frequency ω ₁ to the value of the calibration radio frequency field H ₁ .

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