= Cross-polarization (nuclear magnetic resonance)
<Cross-polarization (nuclear magnetic resonance)> transfers nuclear spin <nuclear spin polarization> between different nuclear populations, commonly from abundant <hydrogen> nuclei to dilute <carbon-13> nuclei in a solid. Applied <radio frequency> fields bring the two spin populations into a condition that permits polarization exchange through magnetic dipolar coupling.<Proton-enhanced NMR of dilute spins in solids by Alexander Pines and others>[Abstract and experimental method: abundant-to-rare spin transfer]{ref}
For on-resonance spin locking, an ideal matching condition is $|\gamma_I|B_{1I}=|\gamma_S|B_{1S}$, where $\gamma$ is the <gyromagnetic ratio> and $B_1$ is the applied transverse field amplitude for each population. The fields match motion in the respective rotating frames, even though the nuclei have different laboratory resonance frequencies. This can enhance a weak carbon signal, but intensity also depends on transfer and relaxation, so peak areas need not directly count atoms without further controls.<Proton-enhanced NMR of dilute spins in solids by Alexander Pines and others>[Theory of polarization transfer and dependence on contact conditions]{ref}
Back to article page
