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Nuclear Magnetic Spin Noise in Imaging and Spectroscopy

Felix Bloch [1] first predicted nuclear spin noise in 1946, experimentally it was first detected in 1985 [2]. With state-of-the-art high-resolution NMR spectrometers, in particular when using cryogenically cooled probes, observation of spin noise phenomena is fairly straightforward today. We used it previously to image proton spin density without excitation [3]. Quantification of spin noise amplitudes and understanding of the line shapes are complicated. Only if radiation damping is quenched, e.g. by a static field gradient, linear dependence between the power spectral amplitude and the number of spins can be observed, as is the case in imaging [3]. The dependence of spin noise line shapes on the tuning of the receiving resonance circuit is illustrated in the Figure. The large offset of -570 kHz between the conventional tuning optimum and the "spin noise tuning optimum" - SNTO is a significant deviation from what one intuitively expects and from what is predicted by the formalism by Ernst and McCoy [4] This tuning dependence may be used optimise NMR probes. [1] F. Bloch, Phys. Rev. 70 (1946) 460– 475. [2] T. Sleator, E. L. Hahn, C. Hilbert, J. Clarke, Phys. Rev. Lett. 55 (1985) 1742– 1746. [3] N. Müller, A. Jerschow, Proc. Nat. Acad. Sci. (USA) 103 (2006) 6790– 6792. [4] M. A. McCoy, R. R. Ernst, Chem. Phys. Lett. 139 (1989) 587– 593. Acknowledgement This research is supported by the Austrian Science Funds FWF, project P19635-N17 (to N.M.), the ÖAD (WTZ AT-HR, to N.M.), a grant to A.J. by the US NSF (CHE-0550054), and by the Croatian Ministry of Science, Education and Sports (project 098-0982929-2917, to V.S.)

NMR spectroscopy; spin noise spectra

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