engleski

Spin noise: Non-linear effects

We recently focused research on the fundamentals of spin noise in NMR spectroscopy and systematic assessment of experimental spin noise phenomena. Quantification of spin noise amplitudes and understanding of the line shapes are complicated due to the effects of radiation damping. 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 was the case in our earlier study [1]. The complexity of the dependence of spin noise line shape on the tuning of the receiving resonance circuit mentioned previously is of particular interest. The large offset of -570 kHz between the conventional tuning optimum and the “ spin noise tuning optimum” - SNTO, deviates significantly from what one intuitively expects and also from what is predicted by the formalism by Ernst and McCoy [2]. This tuning dependence may be used to optimise tuning and as a guide for optimising the resonance circuits in magnetic resonance probeheads. Under SNTO-conditions the amplitude of the spin noise power may even decrease with increasing number of spins. Also notably different behavior is found for conventional and cryo probes [3]. References [1] Müller, N. and Jerschow, A. (2006) Proc. Nat. Acad. Sci. (USA) 103, 6790-6792. [2] McCoy, M.A. and Ernst, R.R. (1989) Chem. Phys. Lett. 139, 587-593. [3] Nausner, M., Schlagnitweit, J., Smrecki, V., Yang, X., Jerschow, A., , Müller, N. (2009) J. Magn. Reson., in print. 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

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