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ST35 - Low-field NMR Measurement Procedure when SQUID Detection is Used
Low-field NMR Measurement Procedure when
Longqing Qiu1,2, Yi Zhang1, Hans-Joachim Krause1, Alex I. Braginski1
Abstract - In reported low-field nuclear magnetic resonance (NMR) measurements using SQUID (Superconducting Quantum Interference Device) detection, the pre-polarizing magnetic field has been oriented orthogonal to the measuring field, Bp ⊥ Bm. Melton et al. were first to analyze the consequences of Bp decay in time after turnoff and showed that this decay should be nonadiabatic. We evaluated the SQUID-based measuring procedure in the light of Melton et al. analysis, found good quantitative agreement, and showed that, when the decay time constant is comparable to the precession time of the magnetic moment vector M, the optimum procedure is to orient Bp parallel to Bm and to apply a π/2 pulse to flip M, similar as in the case of conventional NMR.Received June 21, 2008. Accepted June 25, 2008. Reference No. ST35; Category 4.
Paper submitted to a peer-reviewed journal.