size of an atomic nucleus is far too small to image its features directly with a microscope, the interaction of an atomic nucleus with electrons bound to it will leave signatures of the size and shape of the nucleus on the the resulting atom in the form of hyperfine structure (HFS). In particular, $P$ and $T$ symmetries dictate that the distribution of protons leads to even-rank $(k\!=\!0,2,4...)$ electric $2^k$-pole moments (e.g., monopole, quadrupole, and hexadecapole) and the distribution of currents and magnetic moments leads to odd-rank $(k\!=\!1,3,5...)$ magnetic moments (e.g. dipole, octupole, and 32-pole) that interact with the electrons to shift their energies. In this sense, when combined with accurate atomic structure calculations, a measurement of the HFS of an atom constitutes an electron scattering experiment on the nucleus that allows us to “see” the distribution of its nucleons by observing how these well-characterized electrons scatter from it.

In general, the dominant contributions to HFS come from (nuclear) magnetic dipole and electric quadrupole interactions. Presently, the nuclear magnetic dipole ($\mu$) and electric quadrupole ($Q$) moments of most nuclei are well established (see e.g., compilation [@Stone2005]). This is largely because the HFS signatures of higher-order moments only appear on electronic states 