Isotopes are the same atoms except that they have a different amount of neutrons. The most popular isotopes are probably thoses of uranium : U238, which accounts for 99.275% of the uranium found in nature, and U235, which is used in nuclear power plants. However, the isotopes of hydrogen also are important. They are what we are going to present here.

This article is a part of our dossier on hydrogen, innovation and ecology.

Hydrogen isotopes

The hydrogen atom can have 7 isotopes. However, 4 are mostly theoretical, being too unstable. We will talk about the 3 most common : protium, deuterium and tritium.

Hydrogen 1, 1H, Protium

The “normal” hydrogen atom is composed of one proton and no neutron. It’s called hydrogen 1, protium, light hydrogen, H-1 or 1H. It’s atomic mass is 1,007u.

Hydrogen 2, 2H, deuterium

The deuterium nucleus (deuteron) combines a proton and a neutron. It’s called heavy hydrogen, hydrogen 2, 2H, D or H-2. It was discovered in 1931 by Harold Clayton Urey.

It is a stable, non-radioactive atom, found in nature in very small proportions. There is on average, for example, 32.4g/m3 in seawater (=32.4mg/L).

Hydrogen 3, 3H, tritium

The nucleus of tritium (triton) combines one proton and 2 neutrons. It was discovered in 1934, by Ernest Rutherford. It’s also called hydrogen 3, 3H, T or H-3.

It is an unstable, radioactive atom. However, it is found in nature (1 atom for 1018 hydrogen atoms) or as a release from the nuclear industry. In France, it is stored on the site before being rejected under certain conditions. The atomic mass of tritium is 3.016u.

Practical applications of hydrogen isotopes

The 2H and 3H hydrogen isotopes will be used in various ways:

  • in heavy water
  • in tritiated (or super-heavy) water
  • nuclear fusion
  • atomic bombs
  • various applications, such as biological labeling or luminescence

Heavy water

Heavy water is a water molecule whose hydrogen atoms are deuterium. It’s also called deuterium oxide. It is used :

  • in nuclear magnetic resonance (NMR) spectroscopy;
  • in some nuclear reactors, to slow down the neutrons emitted by nuclear fission (then, it’s called “neutron moderator”) to increase the likelihood that they will trigger new chain reactions;
  • to detect neutrinos.

Historical anecdote: The first heavy water production plant, created in 1934 in Norway, was the stake of several military operations. We talk about the “battle for heavy water“.

Tritiated (or super-heavy) water

Tritiated water is a water molecule whose hydrogen atoms are tritium atoms. It is also called “super-heavy water” or “tritium oxide” and is denoted T2O or 3H2O. By extension, this also designates its (very) diluted forms. It is a major hazardous radioactive waste.

However, it is also used for datation and as a tracer in biological studies.

For nuclear fusion

Tritium might be a key element of nuclear fusion. The latter occurs when electrostatic force (making proton repelling each other) is overwhelmed by the “strong interaction”. Tritium has more neutron, so more “strong interaction”.

Atomic bombs

Deuterium and tritium can also be used to increase the effectiveness of nuclear bombs.

Other uses

Since gaseous tritium is luminescent (it’s the green used to caricature radioactive waste), it can be used in various civilian objects (watches, signs, signs, etc.) in very small quantities.

CEA-Joliot researchers are developing a method for labeling molecules by replacing certain hydrogen atoms with deuterium or tritium.