I'm having some trouble rationalizing why nuclei with low gyromagnetic ratios are considered unreceptive in NMR. I know it's because it will take a higher magnetic field to "hit" its Larmor Frequency (putting aside more advanced techniques like cross-polarization or DNP), but what physical significance does the value have in NMR beyond that? I know it's a ratio of magnetic moment to angular momentum, so could it have to do with speed of Larmor precession that makes it unreceptive, or maybe a smaller population difference due to small spacing between energy levels?

For instance, comparing 103Rh to 1H, both are almost 100% abundant (103Rh is slightly more abundant, in fact), but 1H is enormously more receptive than 103Rh, which I can only attribute to the difference in gyromagnetic ratios since they're both spin-1/2 and don't have a quadrupole moment.

I'd appreciate any direction you could offer!

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    $\begingroup$ The SNR varies as $\gamma^{11/4}$, which is explained further in this question & its answers: chemistry.stackexchange.com/questions/131689 $\endgroup$ Apr 25, 2022 at 0:28
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    $\begingroup$ [For 103Rh specifically, there is another complicating factor in that you need to make sure that you have a probe that can go to such low frequencies... many probes out there only go down to 15N which is still ~3x higher frequency than 103Rh.] $\endgroup$ Apr 25, 2022 at 1:17


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