D

D - diffusion coefficient.

DAC —> Digital to analog converter.

Data system —> Computer.

DB/Dt (delta B/delta t)- the rate of change of the magnetic field (induction) with time. Because changing magnetic fields can induce electrical fields, this is one area of potential concern for safety limits.

Decoupling - when acquiring spectra of nuclei other than protons the effects of proton coupling can be removed (to improve the S/N ratio and simplify the spectra) by applying a train of 180° pulses at the proton frequency while acquiring at the frequency of the other nucleus.

Demodulator - another term for detector, by analog to broadcast radio receivers.

Detector - portion of the receiver that demodulates the RF NMR signal and converts it to a lower frequency signal. Most detectors now used are phase sensitive (e.g. quadrature demodulator/detector), and will also give phase information about the RF signal.

Dewar - thermos container to retain liquid gases, such as helium, at low temperatures (after Sir Janner Dewar).

Diamagnetic - a substance that will slightly decrease a magnetic field when placed within it (its magnetization is oppositely directed to the magnetic field, i.e. with a small negative magnetic susceptibility).

Diffusion - the process by which molecules or other particles intermingle and migrate due to their random thermal motion. NMR provides a sensitive technique for measuring diffusion of some substances.

Digital to analog converter (DAC) - part of the interface that converts digital numbers from the computer into analog (ordinary) voltages or currents; used to generate gradient and RF wave forms.

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