Deuterium is an isotope of hydrogen with atomic mass of 2. It is represented by the symbols 2H or D. Deuterium is also known as heavy hydrogen. The nucleus of the deuterium atom, consisting of a proton and a neutron, is also known as a deuteron and is represented by the symbol d.

The possible existence of an isotope of hydrogen with atomic mass or two was suspected as early as the late 1910s after Frederick Soddy had developed the concept of isotopes. Such an isotope was of particular interest to chemists. Since the hydrogen atom is the simplest of all atoms --consisting of a single proton and a single electron--it is the model for most atomic theories. An atom just slightly more complex-one that contains a single neutron also--could potentially contribute valuable information to existing atomic theories.

Among those who sought for the heavy isotope of hydrogen was...