Long-Lived Spin States in Nuclear Magnetic Resonance

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Nuclear Magnetic Resonance (NMR) is a technique which uses the fact that the nuclei of many atoms act as tiny radiotransmitters, emitting radio signals at precisely-defined frequencies, which can be detected by a carefully-tuned detector. The frequencies and strengths of the signals depend on the magnetic field in which the sample is placed: the higher field, the higher the frequency, and the stronger the signals. In an NMR experiment, the nuclei are first magnetized by placing a sample in a strong magnetic field for some time. A sequence of radiofrequency pulses is then applied to the sample, which then emits radiowaves which can be detected in the radio receiver. The pattern of emitted waves depends on what the nuclei experienced during the pulse sequence. One useful feature is that the nuclei can remember what happened to them some seconds before the radiosignals are emitted. This memory property allows one to track movements such as chemical reactions, the random displacement of molecules, and the flow of blood and other fluids by NMR. Until recently, the memory time of the atomic nuclei was thought to be a fixed property of the substance under study, which could not be changed significantly by the way one does the experiment. However, our group showed in 2004 that for some substances the memory time could be extended by a factor of 10 or more, by applying a certain sequence of radiofrequency pulses. We had demonstrated a new phenomenon which is now called long-lived spin states (LLSS). In this project, we will try to understand the LLSS phenomenon better and learn how to apply it to the study of motional processes. In the long term, this will provide scientists, engineers and doctors with new tools for understanding the behaviour and motion of chemical substances.