= Edward O. Stejskal
{c}
{title2=1932-2011}
= E. O. Stejskal
{c}
{synonym}
\b[Edward O. Stejskal] was a <physical chemistry> researcher known for <nuclear magnetic resonance> methods. His Illinois doctoral work used <nuclear spin relaxation> to investigate molecular motion in solids. At Wisconsin he developed <pulsed field gradient NMR> with his first doctoral student, <John E. Tanner>; later he worked at Monsanto and became a professor at North Carolina State University.<Obituary: Edward Stejskal by the University of Illinois Department of Chemistry>[Graduate research, Wisconsin collaboration, Monsanto and NC State appointments]{ref}
\Image[https://chemistry.sciences.ncsu.edu/wp-content/uploads/sites/455/2025/07/Edward-Stejskal-1-BW.jpg]
{title=Edward O. Stejskal, in the NC State Chemistry in-memoriam faculty directory}
{height=300}
Their 1965 apparatus measured proton <spin echoes> at $20.00\,\mathrm{MHz}$ using opposed gradient coils. Keeping the applied <magnetic field gradient> small during the <radio frequency> pulses and echo detection removed two limitations of continuously strong gradients: difficult excitation across a broad resonance and an echo too narrow to measure easily. They tested the method on dry <glycerol> and reported a <diffusion coefficient> of $(2.5\pm0.2)\times10^{-8}\,\mathrm{cm^2\,s^{-1}}$ at $26\pm1\,{}^{\circ}\mathrm C$. This is their reported measurement, rather than a general reference value for all glycerol samples.<Spin Diffusion Measurements: Spin Echoes in the Presence of a Time-Dependent Field Gradient by E. O. Stejskal and J. E. Tanner>[pp.288–289: measurement motivation; pp.291–292: 20MHz apparatus and glycerol result]{ref}
The <Stejskal-Tanner equation> gives a useful ideal prediction. For unrestricted <diffusion>, two equal rectangular gradient pulses of duration $\delta$ and magnitude $g$, with starting times separated by $\Delta$, give
$$
\frac{S}{S_0}=e^{-bD},\qquad b=(\gamma g\delta)^2\left(\Delta-\frac{\delta}{3}\right).
$$
Here $D$ is the <diffusion coefficient>, $b$ the <diffusion weighting b-value>, and $\gamma$ the angular <gyromagnetic ratio>; $S_0$ is the otherwise matched echo without the applied diffusion-encoding gradients. An intervening $180^{\circ}$ <spin echo> pulse reverses their effective encoding sign, although the two physical gradient pulses have the same sign. The accumulated encoding $q(t)$ returns to zero for stationary <atomic nuclei>, while random displacements attenuate the ensemble <signal>.<Spin Diffusion Measurements: Spin Echoes in the Presence of a Time-Dependent Field Gradient by E. O. Stejskal and J. E. Tanner>[pp.289–290: Theory and rectangular-gradient case]{ref}
\Image[/spin-echo-gradient-timing.png]
{title=An original idealized gradient-pair diagram: identical physical pulses, refocusing of the stationary position tag, and the time integral of squared encoding that determines diffusion attenuation}
The finite-duration correction can be checked directly. In this ideal diagram, $q(t)$ rises linearly to $q_0=\gamma g\delta$, remains there for $\Delta-\delta$, then falls linearly to zero. Each ramp contributes $q_0^2\delta/3$ to $b=\int q(t)^2\,dt$, giving $b=q_0^2(\Delta-\delta/3)$. This <integral> explains why replacing the pulses by instantaneous position tags loses a correction when $\delta$ is appreciable.
At Monsanto, Stejskal and <Jacob Schaefer> combined <cross-polarization (nuclear magnetic resonance)> with <magic angle spinning> to obtain high-resolution <solid-state nuclear magnetic resonance>. In <cross-polarization magic-angle spinning>, polarization transfer strengthens weak nuclear responses while sample rotation averages appropriate anisotropic interactions; the two operations address different experimental obstacles.<Obituary: Edward Stejskal by the University of Illinois Department of Chemistry>[Monsanto collaboration with Jacob Schaefer and combined cross-polarization/magic-angle spinning]{ref}
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