Heavy water

Some water is extra heavy.

This water has special parts. These parts are heavier than normal water parts. Because of this, the water is thicker. It can even sink in regular water.

This water can taste a bit sweet. It does not have a blue color. It also melts at a higher temperature.

People use this water in big machines. It helps make power in nuclear reactors. It is used in many different jobs.

Too much of this water can be bad for living things. It can stop cells from working. But small bits of it are safe for us.

Heavy water is a special kind of water. Most water has light hydrogen atoms. Heavy water uses deuterium. This is a heavy type of hydrogen. A deuterium atom has a neutron. A normal hydrogen atom does not. This makes the atom twice as heavy.

Because it is heavy, this water is different. It is 10.6% denser than regular water. You can see this if you drop heavy ice into normal water. The heavy ice will sink. It also melts at 3.7 °C. This is warmer than regular ice. Some people say heavy water tastes a bit sweet. It also lacks the light blue color of normal water.

Heavy water is very useful. It helps in nuclear reactors. It can slow down neutrons. This helps make power. It is also used to study how bodies work.

However, too much heavy water can be dangerous. It can change how cells work. For most living things, it can be lethal. This happens if more than 50% of their water is heavy water. But small amounts are safe for humans.

Heavy water is a special form of water that behaves differently than the water we drink every day. Most water is made of hydrogen atoms called protium. Heavy water uses a different type of hydrogen called deuterium. A deuterium atom is much heavier because it has a neutron inside its center. A normal protium atom only has a single proton. This extra neutron makes a deuterium atom about twice as heavy as a normal one.

There are many ways to see how heavy water works. It is about 10.6% denser than regular water. If you drop heavy ice into normal water, it will sink to the bottom. Regular ice melts at 0 °C, but heavy ice melts at 3.7 °C. You might also notice that heavy water does not have the light blue color of normal water. This happens because the way the molecules vibrate changes how they absorb red light. Some people even say heavy water tastes slightly sweet.

Scientists first discovered the parts of heavy water in the early 1930s. Harold Urey discovered the deuterium isotope in 1931. Later, his mentor Gilbert Newton Lewis isolated the first pure sample in 1933. In 1934, researchers George de Hevesy and Erich Hofer used it to study the human body. They wanted to see how fast water moves through a person. After nuclear fission was discovered in 1938, heavy water became very important for energy research. It helps manage neutrons in early nuclear experiments.

Heavy water is used in many important ways today. It is used in nuclear reactors to act as a neutron moderator. This is a tool that helps control the speed of neutrons. Some reactors, like the CANDU type, use highly enriched heavy water. These reactors are 99.75% enriched with heavy hydrogen atoms. Heavy water is also used in medical tools like infrared spectroscopy. It can even help in making radioactive materials like plutonium and tritium.

While heavy water is useful, it can be hard on living things. It can change how enzymes and cells divide in bigger living things. If more than 50% of a multicellular organism's water is heavy water, it can be lethal. This is because the heavy atoms change important chemical bonds. However, humans do not need to worry about small amounts. Our bodies naturally contain about five grams of heavy water already. This amount is completely harmless to us.

Heavy water, known scientifically as deuterium oxide (D2O), is a distinct form of water. It is defined by the presence of deuterium, which is a heavy isotope of hydrogen. In most ordinary water, hydrogen atoms consist of a single proton called protium. However, a deuterium nucleus contains both a proton and a neutron. This extra neutron makes a deuterium atom approximately twice as heavy as a protium atom. While a heavy water molecule is heavier, the total mass change is not massive. This is because about 89% of a water molecule's mass comes from the single oxygen atom.

The physical properties of heavy water differ significantly from the light water we use daily. Heavy water is about 10.6% denser than regular water. You can observe this by dropping heavy ice into normal water; the ice will sink. Heavy water also has a higher melting point of 3.7 °C. It lacks the very faint blue color seen in regular water. This occurs because the molecular vibrations shift the absorption of red light into the infrared spectrum. Some humans may even notice a slightly sweet taste due to specific taste receptors.

There are different variations of water containing heavy isotopes. Semiheavy water, or HDO, occurs when both protium and deuterium are mixed. Because hydrogen atoms exchange rapidly between molecules, HDO is much more common than pure D2O. In normal water, about one in 3,200 molecules is semiheavy water. Another type is heavy-oxygen water, which is enriched with heavier oxygen isotopes. This type is denser but lacks the unique nuclear properties of deuterium-based water. Finally, tritiated water contains tritium, which makes the water radioactive.

The history of heavy water is tied to major scientific breakthroughs. Harold Urey, a Nobel laureate, discovered the deuterium isotope in 1931. Shortly after, his mentor Gilbert Newton Lewis isolated the first pure sample using electrolysis in 1933. In 1934, George de Hevesy and Erich Hofer used heavy water for early biological tracer experiments. They used it to estimate how quickly water turns over in the human body. After the discovery of nuclear fission in 1938, heavy water became vital for nuclear energy research.

Heavy water is essential in the field of nuclear engineering. It is used as a neutron moderator, which is a substance that slows down neutrons. Some reactors, such as the CANDU design, use highly enriched heavy water. This mixture is 99.75% enriched by hydrogen atom-fraction. These reactors are useful because they can run on natural uranium. This avoids the need for graphite moderators, which can pose explosion hazards during decommissioning. Heavy water also helps in the production of radioactive materials like plutonium and tritium.

Beyond energy, heavy water has many specialized industrial uses. It is used in nuclear magnetic resonance and infrared spectroscopy. It also plays a role in neutrino detection and neutron capture therapy. Scientists use it for metabolic rate testing and in the production of radiopharmaceuticals. The most cost-effective way to produce it is through the Girdler sulfide process. It is sold in various grades of purity depending on the specific scientific or industrial need.

Heavy water has complex effects on biological systems. It can alter enzymes, hydrogen bonds, and the way cells divide in eukaryotes. For multicellular organisms, replacing more than 50% of their water with heavy water is lethal. This is because the heavier atoms change important biochemical reactions. However, humans are naturally safe around small amounts. The human body already contains about five grams of heavy water. While it can be toxic in large amounts, it is not a constant threat to life.