heavy water

noun

1. water in which hydrogen atoms have been replaced by deuterium, used chiefly as a coolant in nuclear reactors.

heavy water

noun

1. water that has been electrolytically decomposed to enrich it in the deuterium isotope in the form HDO or D 2 O

heavy water

1. Water in which deuterium, a heavy isotope of hydrogen, takes the place of hydrogen. Heavy water has physical and chemical properties that are like those of ordinary water, but heavy water is 10 percent heavier and has higher freezing and boiling points. Also called deuterium oxide. Chemical formula: D 2 O.
2. ◆ Semiheavy water is similar to heavy water, but only one of the two hydrogen atoms in each molecule is replaced with deuterium. Chemical formula: DHO.

heavy water

1. Water with a higher average molecular weight than ordinary water. In a molecule of heavy water, the hydrogen atoms are isotopes in which the nuclei each contain a proton and a neutron , and hence are twice as heavy as a normal hydrogen atom.

Word History and Origins

Origin of heavy water¹

First recorded in 1930–35

A Closer Look

The nucleus of most hydrogen atoms consists of a single proton, but in one isotope of hydrogen, called deuterium or heavy hydrogen, the nucleus also contains a neutron and thus weighs nearly twice as much as standard hydrogen. The substance called heavy water is chemically identical to ordinary water (H 2 O), except that the hydrogen atoms in the molecule are the deuterium isotopes (D 2 O). Heavy water makes up a small percentage (0.02%) of water naturally occurring on Earth. It is an excellent moderator for nuclear reactions, slowing down the fast neutrons produced in a nuclear fission reaction, increasing the likelihood that the neutrons will successfully collide with heavy nuclei to cause further fission. Although heavy water is chemically nearly identical with ordinary water, it is about ten percent heavier and interferes with cell mitosis if consumed in place of normal water. Ice cubes made of heavy water are denser than ordinary liquid water and will sink to the bottom of a glass of cola.

Example Sentences

Water molecules made of heavier deuterium instead of ordinary hydrogen are known, straightforwardly enough, as heavy water.

From Time

“Heavy water”, or D2O, is even less common in nature, though nuclear engineers make and use it in some reactors.

From The Daily Beast

The heavy water Arak reactor is scheduled to become active in the summer of 2014.

From The Daily Beast

By the summer of 2014, the heavy water Arak reactor is scheduled to become active.

From The Daily Beast

Better founded was the statement that “heavy water”—a water in which no animal life, however small, could live—had been produced.

From Project Gutenberg

At his side lay the torso of the young reporter, his head mashed by the heavy water-cooler.

From Project Gutenberg

There is the artistic excitement of choosing the hook, gaudy for a heavy water, neat and modest for a clearer stream.

From Project Gutenberg

The trout were all onannaniche and as game a fish for its size as I ever want to catch; in the heavy water they gave grand sport.

From Project Gutenberg

Anthea lifted down the heavy water-jug—it had a pattern of storks and long grasses on it, which Anthea never forgot.

From Project Gutenberg