Dynamic Nuclear Polarisation And Non-Equilibrium Physics

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Dyamic Nuclear Polarisation (DNP) is a technique that makes it possible to enhance the signal and hence the sensitivty of magnetic resonance imaging (MRI) and nuclear magnetic resonance (NMR) spectroscopy. MRI is one of the key modalities in medical diagnostics and NMR spectroscopy is widely used in biomolecular research for structural investigation and in material research for probing molecular properties. The fundamental principle of these techniques is the detection of a weak sample magnetisation that arises from placing the sample (small as in the case of NMR spectroscopy or large as in the case of medical whole body imaging) in a strong magnetic field generated by a magnet. The strong magnetic field interacts on the atomic level with some nuclei (e.g. hydrogen 1H or the stable carbon isoptope 13C) and also any unpaired electron since these nuclei or the electron have also a magnetic moment. In a simple explanation one can envisage the nuclei or the unpaired electron to either align parallel or unparallel with the direction of the external magnetic field. There is a small difference in the order of a few ppm in the number of nuclear that align parallel and antiparallel with the magnetic field and this difference between these two groups gives rise to the signal used in MRI or NMR. If it would be possible to align all nuceli in the same orientation the signal would dramatically increase. However, the thermal energy in the sample usually prevents the perfect alignment but it has been shown that the nuclei can be aligned with the help of unpaired electrons. The process of aligning nuclei with the help of electrons is called DNP. The underlying physics is complex because all nuclei interact with each other as well as with the electron and the alignment process follows the rules of quantum mechanics. Interestingly, we have recently discovered that some of the dynamical aspects in a large system containing many interacting nuclei and an electron are identical to properties of other systems containing a large number of interacting particles such as for instance systems changing their state in a glass transition. In our project we will investigate the links between DNP and other non-equilibrium systems to find out whether such systems share more common properties which perhaps can be described by generalising rules. Furthermore, we propose to develop models that predict the dynamics of systems of many nuclei during DNP experiments. The goal here is to gain enough insight so that DNP experiments can be made more efficient by providing even a higher signal enhancement in a shorter time.