Scientists have discovered a new type of uranium that is the lightest ever known. The discovery could reveal more about a weird alpha particle that gets ejected from certain radioactive elements as they decay.

The newfound uranium, called uranium-214, is an isotope, or a variant of the element, with 30 more neutrons than protons, one fewer neutron than the next-lightest known uranium isotope. Because neutrons have mass, uranium-214 is much lighter than more common uranium isotopes, including uranium-235, which is used in nuclear reactors and has 51 extra neutrons.