Fermi’s ground-breaking figure: How the radial wave function transformed physics

One way to better understand an atom is to shoot a particle at it and infer the atom’s properties based on how the particle bounces off it. In the mid-1930s, the physicist Enrico Fermi showed that one measurable number—the scattering length—illuminated everything that could be known about an electron scattering off an atom, or a neutron scattering off a nucleus.