Using heavy-ion collisions at the LHC, scientists determine the thickness of neutron 'skin' in lead-208 nuclei

Lead-208 has an intriguing nucleus. It is neutron rich, containing 82 protons and 126 neutrons. One of its more interesting properties is its structure: its center is composed of both protons and neutrons, but at its edge, there is a diffuse shell of mostly neutrons. Scientists call this the neutron "skin."