polarization time | Energy Glossary

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polarization time

1. n. [Formation Evaluation]

The time allotted for the alignment of the spins of hydrogen atoms with the static magnetic field during a nuclear magnetic resonance (NMR) measurement. The alignment follows an exponential rule such that, after a polarization time PT, the fraction of aligned spins is 1 – e–PT/T1, where T1 is their longitudinal relaxation time. An infinite polarization time is therefore needed to full polarization, but 95% polarization is reached after a time of 3*T1. Typical acquisition polarization times for a standard NMR log are between 1 and 4 s, mostly depending on the acquisition sequence and logging speed. Some tools benefit from prepolarization with an asymmetrical permanent magnet so that the effective polarization time may be larger than the acquisition polarization time. (An example is the CMR tool.)

See: nuclear magnetic resonancenuclear magnetic resonance measurementwait time