protium

noun2

1. •
   The lightest and most common isotope of hydrogen, having a single proton and no neutrons: 11H. It is the only stable nuclide with no neutrons.

   • So far there are no differences among the protiums extracted at various labs, except for concentration levels.
2. •
   An atom of this isotope.

   • This radioactive decay leaves behind a protium as well.