Deuterium

Scientists from the Lawrence Livermore National Laboratory report they were able to create a type of fusion reaction by bombarding a microscopic pellet of fuel with beams from 192 powerful lasers to compress its component parts — hydrogen isotopes known as deuterium and tritium — and fuse them together at the atomic level.

Heavy water is "heavy" because it contains deuterium.

There were about 80 deuteriums for every million protiums, and virtually no tritium.