Spin dynamics and optimisation of dynamic nuclear polarisation at cryogenic temperatures

核磁共振（NMR）是一种基于测量弱样品磁化强度的技术，该弱样品磁化强度是由强外部磁场与样品中携带磁矩的各种类型的原子核相互作用产生的。由外部磁场对核的磁矩产生的相互作用力倾向于使核在平行于外部场方向的取向上对准。然而，热运动抵消了这种对准，并且由于外部场和磁矩之间的相互作用力仅非常弱，因此在具有平行对准的核的群体与在相反（或反平行）方向上对准的自旋的群体之间仅存在小的差异。这就是为什么核磁共振技术通常被认为是不高灵敏度的原因。热运动可以通过使用液氦将样品冷却到非常低的温度来减少。因此，样品磁化强度增加。未成对电子具有磁矩，并且与外部磁场的相互作用比质子强约3个数量级，其温度为1K，外部磁场为3.5T，几乎完全与外部磁场的方向对齐。在NMR术语中，这意味着电子100%极化。未成对电子耦合到磁活性核自旋，并且可以使用这种相互作用将电子极化转移到磁活性核上。原则上，电子被用来使原子核在一个方向上排列。这个过程被称为动态核极化。这个过程的动力学可以用量子力学推导出来。然而，量子力学的数学公式意味着，如果假设一个系统有许多耦合的原子核，这个问题就变得很难解决。本文研究了获得多自旋耦合系统动力学信息的数学策略。此外，测量使模型计算有意义所需的系统参数。在第二步策略进行了研究，在理论上和实验实施，以优化电子系统和核系统之间的极化转移。该项目的主要目标是深入了解动态核极化的动力学，然后使用这些信息来产生更高水平的核极化在更快的时间尺度。该项目的成果将有利于许多应用核磁共振光谱和磁共振成像，这是由低灵敏度的限制。使用有效的DNP策略将有可能产生高极化，用于分子动力学的研究，或者还用于通过对预极化分子的分布和代谢转化进行成像的医学诊断的应用。

Nuclear Magnetic Resonance (NMR) is a technique that is based on the measurement of a weak sample magnetisation that arises from the interaction of a strong external magnetic field with various types of nuclei in the sample which carry magnetic moments. The interaction force generated by the external magnetic field on the magnetic moments of the nuclei tends to align the nuclei in an orientation parallel to the external field direction. However, thermal motion counteracts this alignment and since the interaction force between external field and magnetic moments is only very weak there is only a small difference between the population of nuclei that have a parallel alignment and the population of spins that are aligned in the opposite (or anti-parallel) direction. This is the reason why NMR techniques are usually considered to be not highly sensitive.The thermal motion can be reduced by cooling the sample to very low temperatures using liquid helium. As a consequence the sample magnetisation increases. Unpaired electrons, which possess a magnetic moment and which interact about 3 orders of magnitude stronger than protons with the external magnetic field are at a temperature of 1K and a modest external magnetic field of 3.5T almost fully aligned with the direction of the external field. In NMR terminology this means that the electrons are 100% polarised. Unpaired electrons couple to magnetically active nuclear spins and it is possible to use this interaction to transfer the electronic polarisation onto the magnetically active nuclei. In principle, the electrons are used to align the nuclei in one direction. This process is called dynamic nuclear polarisation. The dynamics of the process can be derived using quantum mechanics. However, the mathematical formulation of quantum mechanics means that the problem becomes difficult to be solved in case a system of many coupled nuclei is assumed. This proposal investigates mathematical strategies to obtain the dynamical information for systems of many coupled spins. Furthermore, the system parameters are measured that are needed to make the model calculations meaningful. In a second step strategies are investigated in theory and afterwards in experimental implementations to optimise the transfer of polarisation between the electron system and the nuclear system.The key objective of this project is to gain insight into the dynamics of dynamics nuclear polarisation and then use this information to generate higher levels of nuclear polarisation on an even faster time scale. The outcome of the project will benefit numerous applications of nuclear magnetic resonance spectroscopy and magnetic resonance imaging which are limited by the low sensitivity. Using efficient DNP strategies is will be possible to generate high polarisation for studies of molecular dynamics or also for applications of medical diagnostics by imaging the distribution and metabolic conversion of pre-polarised molecules.