Spinnoise gradient echoes.

Victor V Rodin,Stephan J Ginthör,Hervé Desvaux,Norbert Müller,Matthias Bechmann

doi:10.5194/mr-2-827-2021

Abstract

Nuclear spinnoise spectroscopy in the absence of radio frequency pulses was studied under the influence of pulsed field gradients (PFGs) on pure and mixed liquids. Under conditions where the radiation-damping-induced line broadening is smaller than the gradient-dependent inhomogeneous broadening, echo responses can be observed in difference spectra between experiments employing pulsed field gradient pairs of the same and opposite signs. These observed spinnoise gradient echoes (SNGEs) were analyzed through a simple model to describe the effects of transient phenomena. Experiments performed on high-resolution nuclear magnetic resonance (NMR) probes demonstrate how refocused spin noise behaves and how it can be exploited to determine sample properties. In bulk liquids and their mixtures, transverse relaxation times and translational diffusion constants can be determined from SNGE spectra recorded following tailored sequences of magnetic field gradient pulses.

Highlights

Felix Bloch (Bloch, 1946) predicted nuclear spin noise (SN) more than 70 years ago as the result of incomplete cancellation of random fluctuations of spin polarization
To observe the described phenomena, a cryogenically cooled high-resolution liquid nuclear magnetic resonance (NMR) probe optimized for 1H detection is used to acquire short noise blocks without any prior radio frequency (RF) excitation but in the presence of and/or preceded by linear magnetic field gradients aligned along the static magnetic field axis (z)
The z gradients are chosen to be sufficiently strong in order to observe an increase in noise power at the nuclear spin resonances and to avoid the nonlinear distortions observed for weaker gradients

Summary

Introduction

Felix Bloch (Bloch, 1946) predicted nuclear spin noise (SN) more than 70 years ago as the result of incomplete cancellation of random fluctuations of spin polarization. After the first experimental observation of a weak nuclear quadrupole resonance (NQR) noise spectrum by Sleator (Sleator et al, 1985), SN has become a subject of renewed and increased interest (Guéron and Leroy, 1989; Marion and Desvaux, 2008; McCoy and Ernst, 1989; Müller and Jerschow, 2006; Pöschko et al, 2017). It has a really appealing potential for studying nanoscale samples (Nichol et al, 2014). Nuclear spin noise accumulated in the presence of magnetic field gradients applied in different directions was used to implement spin noise imaging in the absence of any RF pulses applying a projection–reconstruction approach for data processing (Müller and Jerschow, 2006)

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Conclusion