Charge radius

The charge radius of an atomic nucleus tells its size. The nucleus (center) of an atom is incredibly tiny. A nucleus, as with an atom, is actually a hazy quantum-mechanical wave-cloud, because each of the particles inside it are also hazy wave-clouds. Not having a definite surface, the cutoff is usually statistical, and can be calculated in a variety of ways.

The rms charge radius is a measure of the size of an atomic nucleus, particularly the proton distribution. The proton radius can be measured by the scattering of electrons by the nucleus. Relative changes in the mean squared nuclear charge distribution can be precisely measured with atomic spectroscopy.