Antiprotonic Helium

Antiprotonic helium is a three-body atom composed of an antiproton and an electron orbiting around a helium nucleus. It is thus made partly of matter, and partly of antimatter. The atom is electrically neutral, since both electrons and antiprotons have a charge of -1, whereas helium nuclei have a charge of +2. The antiprotonic helium atom is called an atomcule, as it has a structure like an atom, but has two nuclei like a molecule.