We can interact with nuclei by the radiation they emit or absorb. Just as we describe the shape of the nucleus by multipole components, the properties of the emitted radiation can be described in a multipole framework as well. We will need this to some extent in hyperfinecourse B, on experimental methods based on hyperfine interactions. The general concept is described in this video. If you want to dig deeper (optional), then the Wikipedia entry given under the video is a good start.
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