= Jacob Schaefer
{c}
{title2=1938-2022}
\b[Jacob Schaefer] was a <physical chemistry> researcher who developed methods for studying complex solid materials using <solid-state nuclear magnetic resonance>. After his 1964 doctorate he worked at Monsanto, then joined Washington University in 1986. His contributions included <cross-polarization magic-angle spinning> with <Edward O. Stejskal> and <rotational-echo double resonance> with <Terry Gullion>.<Jacob Schaefer obituary by Washington University in St. Louis>[Education, appointments and joint CPMAS/REDOR contributions]{ref}
\Image[https://source.washu.edu/app/uploads/2017/01/201612_JakeSchaefer-206x300.jpg]
{title=Jacob Schaefer, in the portrait accompanying Washington University's institutional memorial}
{height=300}
The materials in the 1976 <cross-polarization magic-angle spinning> demonstration made the method's reach tangible. They included <polysulfone>, ebony wood and a cylinder cut from an <ivory> billiard ball. Schaefer's father and grandfather were billiards champions; a familiar object became a specimen for measuring <carbon-13> responses in a complex solid. Combining polarization transfer with <magic angle spinning> made weak and broadened solid-state responses much more accessible.<Jacob Schaefer, 1938-2022 by Lynette Cegelski and Terry Gullion>[Tribute: family connection,1976 sample choices and high-sensitivity/high-resolution CPMAS demonstration]{ref}
<REDOR> addresses another measurement problem. <Magic angle spinning> averages interactions that broaden spectra, but some of those interactions carry structural information. Appropriately timed <radio frequency> pulses restore sensitivity to <NMR dipolar coupling> between different nuclear species. Comparing a reference echo with a deliberately dephased echo then probes that coupling, with structural interpretation supplied by a suitable spin model.<Development of REDOR rotational-echo double-resonance NMR by Jacob Schaefer (2011)>[pp.421–422: replacing spin-lock fields with pulses, echo dephasing and weak heteronuclear coupling]{ref}
Schaefer reproduced a laboratory record from 29 May 1987 in which Gullion measured <carbon-13> spectra of <nitrogen-15>-labelled <alanine>. Carbon remained at natural isotopic abundance. The record compares full and dephased echoes at a carbon frequency of $50.3\,\mathrm{MHz}$, using <magic angle spinning> at $3.2\,\mathrm{kHz}$ and 10 rotor periods of dipolar evolution. The corresponding duration is
$$
\boxed{T=\frac{10}{3200\,\mathrm{s^{-1}}}=3.125\,\mathrm{ms}.}
$$
The reproduced record does not give sample mass or number of accumulated scans. Later use of <XY8> <NMR phase cycling> suppressed pulse-train amplitude and phase errors, enabling measurements of weaker couplings over longer pulse trains.<Development of REDOR rotational-echo double-resonance NMR by Jacob Schaefer (2011)>[p.422, Figure1 caption: sample, frequencies and missing acquisition quantities; following paragraphs: XY8 and weak-coupling measurements]{ref}
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