Hui Dong et al 2008 Supercond. Sci. Technol. 21 115009 doi:10.1088/0953-2048/21/11/115009
Hui Dong, Yongliang Wang, Shulin Zhang, Yue Sun and Xiaoming Xie1
Show affiliationsNuclear magnetic resonance in the Earth's magnetic field was studied in an urban laboratory without shielding using a second-order low-Tc SQUID (superconducting quantum interference device) gradiometer. Two different configurations were investigated, one with a prepolarization field perpendicular to the measurement field and the other one with the two fields parallel but a π/2 AC pulse applied perpendicular to them. With a prepolarization field of 10 mT and a measurement field of ~29.1 µT, the proton signal from 15 ml tap water was obtained in a one-shot measurement with high signal-to-noise ratio, and the signal was still discernible down to a sample volume of 2–3 ml. Spin–lattice relaxation time T1~1.78 s was measured from the variation of signal magnitude on the prepolarization time. Spin–spin relaxation time T2 was estimated to be around 0.9 s from the calculated FID signal by using a special method developed based on the principle of a lock-in amplifier.
85.25.Dq Superconducting quantum interference devices (SQUIDs)
Issue 11 (November 2008)
Received 24 June 2008, in final form 20 August 2008
Published 9 September 2008
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