Konzeption und Realisierung eines Messsystems für Grundlagenexperimente in der Niedrigfeld-Magnetresonanz
The presented measurement device for low field nuclear magnetic resonance uses superconductingquantum interference devices (SQUIDs) as detectors for the measurement of the nuclear magnetic precession of liquids. It is operated inside the Berlin Magnetically Shielded Room-2 (BMSR-2) in which the lowest reachable magnetic field and magnetic field gradients are <1 nT and <12 pT/cm, respectively. For the measurements of the nuclear magnetic resonance of liquid samples two independent magnetic fields are used. The polarization field of the sample volume is within 3.1 mT.The detection field used in this work can be varied between 100 nT up to 50 µT. Both magnetic fields are generated by Helmholtz coils. The relative field inhomogeneity of the detection field coil is 70 ppm. The static residual field gradient over the sample volume is about 85 pT/cm. This gradient is mainly caused by the used polarization coil. For the complete set-up a noise level of <15 fT/root(Hz) for frequencies above 4 Hz and <6 fT/root(Hz) for frequencies above 20 Hz was reached, respectively. The new measurement device enables the observation of low frequencymolecular dynamics in a field range far below 50 µT. Within the technical parameters inside the magnetically shielding basic investigations of water become possible in a field range up to now unexplored. The measurement device allows the determination of the T1- and T2-relaxationtimes of liquids in a field range below the Earth magnetic field down to 100 nT for the first time.The experiments described in this work show e.g. the frequency dependent spectral line width of a water sample with different pH-values and different concentrations on the oxygen isotope 17O. Thereby we found a new in the literature not described characteristics of water. Additionally to the known broadening of the spectral line width of water below 25 µT the line width becomes narrower below 5 µT. A phenomenological description for the findings is given were the physical observables are attributed to model parameters.