RU2086967C1 - Method of mutation relaxometry - Google Patents

Abstract

FIELD: study of structure of chemical compounds. SUBSTANCE: method includes periodic action on specimen by two HF pulses with carrier frequency equalling the frequency of excited transition, saturation, detuning and determination of time T₂₉ of transverse relaxation in rotating coordinate system. Object of investigation is used in form of specimen having quadrupole nuclei with multilevel energy spectrum. First, specimen is acted upon by single pulse with carrier frequency equalling the frequency of transition having common energy level with exciting transition. Pulse duration is set within the ranges T $\genfrac{}{}{0ex}{}{\text{*}}{\text{2}}$ < t_w< T₂, and amplitude is set by maximum each signal whose envelope is used to find transverse relaxation time T₂₈ of transition on which single pulse acts. EFFECT: higher efficiency. 1 dwg

Description

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

A known method of nutational relaxationometry, including exposure to a sample with alternating radio frequency and constant magnetic fields under resonance conditions, saturation, detuning and determining the time of longitudinal T _2ρ relaxation in a rotating coordinate system (VSC) [1]
The disadvantage of this method is that it does not provide for the measurement of the transverse relaxation time T _{2ρ in the SSC} , which is an important source of information about the internal structure of the sample under study and spin-spin and spin-lattice interaction processes.

A known method of nutational relaxationometry, including periodic exposure to a sample with two RF pulses with a filling frequency equal to the frequency of the excited transition, saturation, proofing and determining the time of transverse relaxation in a rotating coordinate system (VSC) [2]
This method also has a disadvantage. Its sensitivity and accuracy are small, especially for samples for which, at some transitions, the observation of echo signals is impossible or difficult (but which can be excited), but the relaxation parameters must be determined.

The objective of the invention is to develop a method for determining the transverse relaxation time T _2ρ in a rotating coordinate system (VSC) for transitions at which the observation of echo signals is impossible or difficult, but which can be excited.

This problem is solved using the essential features indicated in the claims: common with the prototype method of nutational relaxationometry, which includes periodic exposure of the sample to two RF pulses with a filling frequency equal to the frequency of the excited transition, saturation, detuning, and determination of the transverse relaxation time T _2ρ in the rotating coordinate system and distinctive from the closest analogue of the essential features as the object of study using a sample containing quadrupole nuclei from multilevels the energy spectrum, which is first affected by a single pulse with a filling frequency equal to the frequency of a transition having a common energy level with an excited transition, the duration of a single pulse is set within T $\genfrac{}{}{0ex}{}{\text{*}}{\text{2}}$ <t _w <T ₂ and the amplitude is the maximum of the echo signal, along the envelope of which the transverse relaxation time T _{2ρ of the} transition, which is _{affected by} a single pulse, is found.

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

 First, for the first time, a two-frequency action is used to form an echo signal in a rotating coordinate system in a multi-level spin system.

Secondly, for the first time under two-frequency action, the transverse relaxation time T _2ρ is determined in a rotating coordinate system.

Thirdly, for the first time, a method is proposed that allows one to determine T _2ρ at a transition at which either an echo signal is not observed, or its amplitude is small.

 An analysis of all the distinguishing features of the present invention showed that the inventive step was high before such techniques were not used for such a task.

 The drawing shows a pulse program of a two-frequency excitation of the echo signal in a rotating coordinate system. The method is implemented using the device described in A.S. N 1132207, G 01 N 24/10, 1984, Bull. N 48.

consider an example of the implementation of the proposed method. A single pulse, the duration of which is set within T $\genfrac{}{}{0ex}{}{\text{*}}{\text{2}}$ <t _w <T ₂ acts on the transition 1 / 2-3 / 2 (ω ₁ ) After a time τ ₁ on the transition 3 / 2- -5/2 (ω ₂ ) the first acts, then after time τ _{2 the} second pulse. At time 2τ ₂ + τ ₁ , an echo signal with amplitude
E ₂ = E _o (1 + α • sin ² βγH ₁ t _w );
Where
E _{0 is the} amplitude of the echo with a single-frequency effect on the transition 3 / 2-5 / 2; α is the ratio of the frequencies of the pumped and observed transitions; b-matrix element of the operator 1 _x in the representation of the full quadrupole Hamiltonian for states between which pumping takes place; g is the gyromagnetic ratio of the nuclei; H ₁ and t _{w are the} amplitude and duration of a single pulse. In this case, the amplitude of a single pulse is set (after setting the duration) to the maximum of the echo signal.

The magnitude of the duration t _{w of a} single pulse is associated with two conditions: saturation and detuning, which are necessary conditions for observing the echo signal in the VSC (both in the case of single-frequency and in the case of two-frequency excitation of the echo signal in VSC).

где
T $\genfrac{}{}{0ex}{}{\text{(I)}}{\text{2}}$ -время поперечной релаксации перехода, на котором действует одиночный импульс; T $\genfrac{}{}{0ex}{}{\text{(II)}}{\text{1}}$ -время продольной релаксации перехода, на котором наблюдается сигнал эхо в ВСК.The envelope of the echo signal (after modulation) decreases exponentially with the time constant T $\genfrac{}{}{0ex}{}{\text{(Ii)}}{\text{2ρ (g)}}$ called T ₂ in a rotating coordinate system with a two-frequency action of a multilevel system. Theoretically, this time is determined by the formula

Where
T $\genfrac{}{}{0ex}{}{\text{(I)}}{\text{2}}$ - time of transverse relaxation of the transition on which a single impulse acts; T $\genfrac{}{}{0ex}{}{\text{(Ii)}}{\text{one}}$ - time of longitudinal relaxation of the transition at which an echo signal is observed in the VSC.

Time t $\genfrac{}{}{0ex}{}{\text{(III)}}{\text{2ρ (g)}}$ found at the 3 / 2-5 / 2 junction under two-frequency exposure is equal to time T $\genfrac{}{}{0ex}{}{\text{(I)}}{\text{2ρ (o)}}$ with a single-frequency effect on the transition 1 / 2-3 / 2. This makes it possible to determine the time T _2ρ in the VSC at the transition where the echo signal is not observed or its amplitude is small.

Let us consider polycrystalline KReO ₄ as an example (resonance of ¹⁸⁵ Re nuclei, I = 5/2, T = 296 K).

При двухчастотном воздействии по программе на чертеже находим:

Отсюда

Таким образом, предлагаемый способ позволяет определять время T_2ρ поперечной релаксации во вращающейся системе координат при двухчастотном воздействии на многоуровневую спин-систему. Кроме того он дает возможность определять T_2ρ на переходе, на котором не наблюдается сигнал эхо (или мала его амплитуда), но на котором можно проводить возбуждение (т.е. вероятность перехода отлична от нуля). В этом случае он позволяет повысить точность и чувствительность.We find that with a single-frequency effect on the transition 1/2 -3/2 - T ₂ = 66 MKs, T ₁ = 260 μs, and when exposed to the transition 3 / 2- -5/2 we find -T ₂ = 100 μs, T ₁ = 250 μs. Transverse relaxation time T $\genfrac{}{}{0ex}{}{\text{(I)}}{\text{2ρ (o)}}$ and T $\genfrac{}{}{0ex}{}{\text{(Ii)}}{\text{2ρ (o)}}$ in a VSK with a single-frequency exposure at each of the transitions is

With two-frequency exposure according to the program in the drawing we find:

From here

Thus, the proposed method allows to determine the time T _2ρ transverse relaxation in a rotating coordinate system with a two-frequency impact on a multi-level spin system. In addition, it makes it possible to determine T _2ρ at a transition at which an echo signal is not observed (or its amplitude is small), but at which excitation can be carried out (i.e., the transition probability is nonzero). In this case, it improves accuracy and sensitivity.

Claims (1)

Method of nutational relaxationometry, including periodic exposure of a sample to two RF pulses with a filling frequency equal to the frequency of the excited transition, saturation, detuning, and determination of the transverse relaxation time T _2ρ in a rotating coordinate system, characterized in that a sample containing quadrupole nuclei is used as an object of study with a multi-level energy spectrum, which is first affected by a single pulse with a filling frequency equal to the frequency of the transition having a common energy matic level with the exciting transition, the duration of a single pulse is set in the range T $\genfrac{}{}{0ex}{}{\text{*}}{\text{2}}$ <t _w <T ₂ , and the amplitude at the maximum of the echo signal, along the envelope of which the transverse relaxation time T _{2ρ of the} transition is found, on which a single pulse acts.