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## #1 2024-03-12 17:32:25

Jai Ganesh
Registered: 2005-06-28
Posts: 47,414

### Heavy water

Heavy water

Gist

Heavy water is a compound that is made up of oxygen and deuterium, a heavier isotope of hydrogen which is denoted by '2H' or 'D'. Heavy water is also called deuterium oxide and is denoted by the chemical formula D2O.

Summary

Heavy water (D2O) is water composed of deuterium, the hydrogen isotope with a mass double that of ordinary hydrogen, and oxygen. (Ordinary water has a composition represented by H2O.) Thus, heavy water has a molecular weight of about 20 (the sum of twice the atomic weight of deuterium, which is 2, plus the atomic weight of oxygen, which is 16), whereas ordinary water has a molecular weight of about 18 (twice the atomic weight of ordinary hydrogen, which is 1, plus oxygen, which is 16).

Ordinary water as obtained from most natural sources contains about one deuterium atom for every 6,760 ordinary hydrogen atoms. and the residual water is thus enriched in deuterium content. Continued electrolysis of hundreds of litres of water until only a few millilitres remain yields practically pure deuterium oxide. This operation, until 1943 the only large-scale method used, has been superseded by less expensive processes, such as fractional distillation (D2O becomes concentrated in the liquid residue because it is less volatile than H2O). The heavy water produced is used as a moderator of neutrons in nuclear power plants. In the laboratory heavy water is employed as an isotopic tracer in studies of chemical and biochemical processes.

Details

Heavy water (deuterium oxide, 2H2O, D2O) is a form of water whose hydrogen atoms are all deuterium (2
H or D, also known as heavy hydrogen) rather than the common hydrogen-1 isotope (1
H or H, also called protium) that makes up most of the hydrogen in normal water. The presence of the heavier hydrogen isotope gives the water different nuclear properties, and the increase in mass gives it slightly different physical and chemical properties when compared to normal water.

Deuterium is a heavy hydrogen isotope. Heavy water contains deuterium atoms and is used in nuclear reactors. Semiheavy water (HDO) is more common than pure heavy water, while heavy-oxygen water is denser but lacks unique properties. Tritiated water is radioactive due to tritium content.

Heavy water (D2O) has different physical properties than regular water, such as being 10.6% denser and having a higher melting point. Heavy water is less dissociated at a given temperature, and it does not have the slightly blue color of regular water. While it has no significant taste difference, it can taste slightly sweet. Heavy water affects biological systems by altering enzymes, hydrogen bonds, and cell division in eukaryotes. It can be lethal to multicellular organisms at concentrations over 50%. However, some prokaryotes like bacteria can survive in a heavy hydrogen environment. Heavy water can be toxic to humans, but a large amount would be needed for poisoning to occur.

Deuterated water (HDO) occurs naturally in normal water and can be separated through distillation, electrolysis, or chemical exchange processes. The most cost-effective process for producing heavy water is the Girdler sulfide process. Heavy water is used in various industries and is sold in different grades of purity. Some of its applications include nuclear magnetic resonance, infrared spectroscopy, neutron moderation, neutrino detection, metabolic rate testing, neutron capture therapy, and the production of radioactive materials such as plutonium and tritium.

Composition

Deuterium is a hydrogen isotope with a nucleus containing a neutron and a proton; the nucleus of a protium (normal hydrogen) atom consists of just a proton. The additional neutron makes a deuterium atom roughly twice as heavy as a protium atom.

A molecule of heavy water has two deuterium atoms in place of the two protium atoms of ordinary "light" water. The term heavy water as defined by the IUPAC Gold Book can also refer to water in which a higher than usual proportion of hydrogen atoms are deuterium rather than protium. For comparison, ordinary water (the "ordinary water" used for a deuterium standard) contains only about 156 deuterium atoms per million hydrogen atoms, meaning that 0.0156% of the hydrogen atoms are of the heavy type. Thus heavy water as defined by the Gold Book includes hydrogen-deuterium oxide (HDO) and other mixtures of D2O, H2O, and HDO in which the proportion of deuterium is greater than usual. For instance, the heavy water used in CANDU reactors is a highly enriched water mixture that contains mostly deuterium oxide D2O, but also some hydrogen-deuterium oxide and a smaller amount of ordinary hydrogen oxide H
2O. It is 99.75% enriched by hydrogen atom-fraction—meaning that 99.75% of the hydrogen atoms are of the heavy type; however, heavy water in the Gold Book sense need not be so highly enriched. The weight of a heavy water molecule, however, is not substantially different from that of a normal water molecule, because about 89% of the molecular weight of water comes from the single oxygen atom rather than the two hydrogen atoms.

Heavy water is not radioactive. In its pure form, it has a density about 11% greater than water, but is otherwise physically and chemically similar. Nevertheless, the various differences in deuterium-containing water (especially affecting the biological properties) are larger than in any other commonly occurring isotope-substituted compound because deuterium is unique among heavy stable isotopes in being twice as heavy as the lightest isotope. This difference increases the strength of water's hydrogen–oxygen bonds, and this in turn is enough to cause differences that are important to some biochemical reactions. The human body naturally contains deuterium equivalent to about five grams of heavy water, which is harmless. When a large fraction of water (> 50%) in higher organisms is replaced by heavy water, the result is cell dysfunction and death.

Heavy water was first produced in 1932, a few months after the discovery of deuterium. With the discovery of nuclear fission in late 1938, and the need for a neutron moderator that captured few neutrons, heavy water became a component of early nuclear energy research. Since then, heavy water has been an essential component in some types of reactors, both those that generate power and those designed to produce isotopes for nuclear weapons. These heavy water reactors have the advantage of being able to run on natural uranium without using graphite moderators that pose radiological[8] and dust explosion[9] hazards in the decommissioning phase. The graphite moderated Soviet RBMK design tried to avoid using either enriched uranium or heavy water (being cooled with ordinary "light" water instead) which produced the positive void coefficient that was one of a series of flaws in reactor design leading to the Chernobyl disaster. Most modern reactors use enriched uranium with ordinary water as the moderator.

What is heavy water?

Heavy water, in simple terms, is water whose hydrogen molecules are exchanged with deuterium (the heavy hydrogen isotope). Therefore, heavy water has a higher boiling point and freezing point than ordinary water. The hydrogen atom has one proton and the deuterium nucleus has one proton and one neutron. This more neutron increases its mass. One mole of ordinary water is 18 grams and heavy water is 20 grams. Therefore, a liter of heavy water has a mass greater than one liter of light water. Due to the difference between the nuclear properties of deuterium and hydrogen in terms of "neutron angular momentum and magnetic moment", heavy water and deuterium are also used in various research fields.

History of heavy water

For the first time, Mr. Russell predicted the existence of deuterium using a helical periodic table. Six years later, in 1931, Harold Yuri of Columbia University discovered it. In 1933, for example, Gilbert Newton-Lewis prepared a sample of pure heavy water by electrolysis. Hossie and Huffer used heavy water in 1944 to conduct environmental tracking experiments to investigate the rate at which water transports through the human body.

How is heavy water produced?

There are various methods including chemical exchange (isotopic), distillation, electrolysis, membrane application, thermal penetration, laser, photochemistry, and adsorption to produce heavy water. Each method has its own advantages and disadvantages and according to the characteristics. So far, only the first three methods have been implemented on an industrial scale. For the first time, the use of the electrolysis (electroplating) method led to the production of heavy water. Since the boiling point of heavy water is higher than ordinary water, evaporation and distillation methods are used to produce it. The difference between the mass of heavy water and light water is considerable and the difference between the boiling points of ordinary water and heavy water is possible. Facilitates the separation of heavy water and its purification. Normally, for every 6,400 to 7,000 ordinary water molecules, there is one heavy water molecule that is physically and chemically purified to produce it.

Heavy water and deuterium applications

The use of heavy water mainly includes two parts: nuclear application and research application (scientific research in the fields of geology, biology, medicine, physics, chemistry, engineering), which we will examine in the following:

Nuclear applications

Neutron Slower: Heavy water is used in some nuclear reactors as a neutron slower. Light water can also be used as a neutron attenuator, but because light water also absorbs thermal neutrons, enriched uranium should be used as fuel in these reactors. But the heavy water reactor can use natural or (unenriched) uranium as fuel. Thus, the production of heavy water is related to the discussion of preventing the proliferation of nuclear weapons. Besides, the use of deuterium and tritium gas for energy production in the fusion process is used. The name helium produces a huge amount of energy.

Non-nuclear applications of heavy water and deuterium

1- Nuclear Magnetic Resonance Spectroscopy: Nowadays, the use of nuclear magnetic resonance spectroscopy (NMR) technique to identify and study the molecular structure is widely used. In this technique, because the signals of the hydrogen atom completely cover the NMR spectrum, heavy water or deuterium solvents are used to study the structure of molecules. Thousands of new compounds are synthesized daily in the world. The first step in identifying these compounds is using the technique. NMR and widespread use of deuterium solvents, the origin of deuterium in deuterium solvents is also heavy.

2. Pharmacy

According to scientists, replacing hydrogen with deuterium improves the properties of drugs and significantly reduces their toxicity. Many companies around the world now produce a variety of deuterium drugs.

3.Use of heavy water in the oil and gas industries:

Today, heavy water is widely used to determine the best location for drilling oil and gas wells and the saturation of such reservoirs.

4. Optical fibers and semiconductors

Another very important application of heavy water is the production of optical fibers and deuterium semiconductors. Replacing deuterium isotopes with hydrogen atoms in these compounds increases their lifespan by up to 10 times and also greatly enhances their electrical properties. Improves a lot. These effects have been such that today leading companies in electronics have started to produce this technology on a commercial level.

5. Deuterium lamp manufacturing industry

These lamps are widely used in spectroscopy devices. In these devices, the source of radiation is deuterium, which provides a continuous source of radiation. A chromatograph menu separates this radiation source and a narrow range of wavelengths is reached to the sample tube by optical instruments. The consumption of deuterium for the production of these lamps is very small, but the price of these lamps is high due to high technology.

6. Neutrino detection. A neutrino detector has been installed deep in the ground in an old mine to prevent cosmic rays from reaching it. The observatory's main goal is to answer the question of whether electron neutrinos produced by fusion in the sun are converted to other types of neutrinos on the way to Earth. Heavy water is essential for these experiments because it provides the deuterium needed to detect a variety of neutrinos.

7- Investigating the energy consumption of living organisms.

A mixture of heavy water with (H218O) water with oxygen whose isotope 18O is used to perform experiments to measure the metabolic rate of humans and animals. This metabolic test is called the DLW "Double Marked Water Test". In this method, the subject first drinks some watermarked with deuterium and oxygen 18 with a specified isotopic concentration.

Then, at specific time intervals, isotopic analysis of D / H and 18O/16O in the urine or saliva sample is performed. Oxygen 18 is excreted from the body in the form of water and carbon dioxide, while deuterium is excreted only in the form of water. Therefore, the difference in the amount of oxygen 18 over a period of time is a reflection of carbon dioxide production. Oxidation of fat is carbohydrate and protein. So the difference in oxygen levels 18 indicates the speed of the body's metabolism.

8- Application of heavy water as a tracer in hydrology

Due to the stability of the deuterium isotope and the absence of any environmental hazard in modern hydrological techniques(stable isotope analysis), by injecting heavy water into groundwater sources, accurate information can be obtained on determining the origin and direction of velocity and direction currents in aquifers. In this method, in groundwater aquifers to determine the path of water movement in porous media, evaluate the groundwater flow velocity, estimate the permeability coefficient of aquifers, origin and feeding ground of groundwater, the relationship of aquifers with each other, and Study of contaminants used.

9_Diagnostic studies in medical science

In general, the basis of nuclear medicine knowledge is the use of radioisotopes and radiopharmaceuticals, and heavy water can be used as a neutron target to produce these materials. Radiopharmaceuticals are used to diagnose and treat diseases such as cancer, benign and malignant tumors, heart failure, and coronary heart disease. For example, in the PET scan technique, labeled glucose or fluorine are widely used. Heavy water is used to label glucose.

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