How2Day: The Effects of Hydrogen Isotopes

Scientists have studied the effects of deuterium oxide on mice. Steve Taylor/Digital Vision/Getty Images
Hydrogen occurs in three different forms called isotopes: protium (ordinary hydrogen), deuterium and tritium. These isotopes differ in the weight of their atoms. A deuterium atom weighs approximately twice as much as a protium atom, and a tritium atom weighs about three times as much. The extra weight of deuterium and tritium alter the properties of hydrogen.

Hydrogen adheres to the surface of such substances as nanoporous carbon--carbon with very tiny pores. The use of a heavier isotope of hydrogen has a significant effect on the hydrogen-adsorbing capacity of nanoporous carbon. At a given temperature, nanoporous carbon can adsorb considerably more deuterium than ordinary hydrogen, according to Bondarenko and Alekseev of the Petersburg Nuclear Physics Institute.

Tritium is a radioactive isotope of hydrogen. Its radioactivity produces definite effects when tritium replaces ordinary hydrogen in organic compounds. For example, introducing tritium into the constituents of paint will produce luminous paint, according to the Los Alamos National Laboratory.

Tritium atoms undergo radioactive decay and change into helium atoms. In this decay process, the volume of the gases present increases. Therefore, if tritium is enclosed in a sealed container, the pressure inside the container will gradually increase, according to Nuclear Power Fundamentals.

All three isotopes become liquids at very low temperature, but when liquid hydrogen is composed of deuterium instead of protium, it boils at a slightly higher temperature, and the boiling point of tritium is even a little higher. The hydrogen isotopes also exhibit a similar variation in their freezing points. The heavier isotopes freeze at a higher temperature than the lighter ones.

The heat of fusion and the heat of vaporization are greater for deuterium and tritium than for ordinary hydrogen. The heat of fusion is the heat required to change hydrogen from a solid into a liquid, and the heat of vaporization is the heat required to change hydrogen from a liquid into a gas.

Since deuterium and tritium atoms have a greater mass than ordinary hydrogen atoms, compounds that contain these heavy isotopes have a greater density than the same compounds containing ordinary hydrogen. For example, deuterium oxide--water that contains deuterium instead of protium--is called "heavy water" because of its greater density, and water containing tritium has an even greater density, according to "General Chemistry" by Linus Pauling.

When deuterium completely replaces ordinary hydrogen in water, the water becomes more viscous. It freezes and boils at slightly higher temperatures than ordinary water. In addition, salt is less soluble in deuterium oxide than in normal water, according to Henry Barbour.

High concentrations of deuterium oxide slow the actions of such enzymes as amylase, which catalyzes the digestion of starch. It depresses heart action and slows respiratory processes. Mice die in a few days when they drink water containing more than 90 percent deuterium oxide, and tadpoles succumb in 15 minutes. Excess deuterium oxide also affects a part of the nervous system called the sympathetic nervous system. This results in such phenomena as an abnormal case of goose pimples and eyes that seem to bulge from the head, according to Henry Barbour.

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