In the periodic table of Dmitry Ivanovich Mendeleev, there is a cell under number 43. For many years, it remained empty. Its inhabitant did not give himself to chemists of the 19th century, hiding from the most persistent hunters for elements. But it turned out that the matter was not in the complexity of separation, but in the very nature of this substance: it simply could not survive on Earth since its formation. Today we know this element as technetium — the first element created artificially, and at the same time the element that saves thousands of lives every day in hospitals around the world.
Tecnecium is the only element lighter than lead that does not have stable isotopes. Its place in the table is a triumph of the predictive power of science and at the same time a monument to human ingenuity.
In 1869, when Dmitry Ivanovich Mendeleev presented his periodic table to the world, there were 63 elements and several empty places in it. He did not just leave gaps — he boldly predicted the properties of yet unknown substances. For the element under number 43, which was located under manganese in the seventh group, the scientist predicted properties, calling it "eka-manganese" (from Sanskrit "eka" — one).
In the following decades, chemists searched for the missing element in manganese ores, minerals, and complex residues of chemical production. There were also loud statements about the discovery: the element was called "ilmium", "nipponium", "lurium". However, none of them was confirmed. Today we know why: technetium is radioactive, and its longest-lived isotopes with a half-life of about 4 million years have long disappeared from the Earth's crust since its formation.
The element received its name from the Greek word "τεχνητός" (technetos), which means "artificial". The name turned out to be prophetic twice: technetium became the first chemical element obtained artificially, not extracted from natural raw materials.
In 1937, Italian physicist Emilio Segre worked in the United States, in the laboratory of Ernest Lawrence — the inventor of the cyclotron. Segre noticed the strange radioactivity of one of the spent parts of the accelerator — molybdenum foil, which served as a target for deuterons.
The scientist assumed that a new element with number 43 was formed in molybdenum (atomic number 42) as a result of nuclear reactions. He took the foil with him to Palermo, where, together with mineralogist Carlo Perrier, he conducted a series of complex chemical operations. They managed to isolate the new radioactive element in pure, albeit microscopic, quantities.
Tecnecium is the lightest element in the periodic table that does not have any stable isotopes. Its "long-lived" forms: Tc-97 (half-life 2.6 million years), Tc-98 (4.2 million years) and the most accessible isotope — Tc-99 (half-life 211,000 years).
At the same time, natural technetium does exist on Earth. In trace amounts (about 1 nanogram per ton of uranium ore), it is formed in the process of spontaneous fission of uranium-235. At any moment, there are about 18,000 tons of technetium in the Earth's crust — but this metal "dissolved" in huge volumes of rock formations.
Physical properties. Tecnecium is a silver-gray transition metal. Its crystal lattice under standard conditions is hexagonal, it is malleable and ductile. Surprisingly, at low temperatures, tecnecium becomes a superconductor.
Chemical versatility. Tecnecium has oxidation states from −1 to +7, and the most stable form is the seven-valent tecnecium (Tc7+). At the same time, chemists often compare it with rhenium. This versatility creates serious problems in the processing of spent nuclear fuel: unpredictable redox reactions involving tecnecium complicate the processes of uranium and plutonium separation.
Today, the vast majority of tecnecium is extracted from the waste of the nuclear industry — from spent fuel rods of nuclear reactors. The yield of the isotope Tc-99 in the fission of uranium-235 is about 6%. However, the focus is not on the long-lived Tc-99, but on its short-lived nuclear isomer — Tc-99m (m means metastable, nuclear excited state) with a half-life of only 6 hours.
This isotope is one of the cornerstones of modern nuclear medicine. Based on it, radiopharmaceuticals are produced for diagnosing malignant tumors, evaluating blood flow in the heart, and studying the functions of many internal organs. The mechanism is as follows: Tc-99m emits gamma rays that are easily detected by special cameras. The isotope is introduced into the body (often in a bound form with molecules tropic to certain tissues) and sends a signal, allowing doctors to "see" a tumor, an inflammation focus, or an area of ischemia in the heart muscle.
The short half-life of the radioactive isotope allows for an accurate picture and quick removal of the substance from the body, causing minimal radiation damage. More than 20 million diagnostic procedures using tecnecium are performed worldwide every year. In Russia, the production of tecnecium-99m generators is carried out by enterprises of the scientific division of "Rosatom".
The long-lived tecnecium-99 (T1/2 = 211,000 years) represents a serious environmental problem. Its content in spent nuclear fuel reaches hundreds of grams per ton. This isotope is mobile in the environment and can accumulate in biological objects. Therefore, the disposal of Tc-99 is one of the tasks when creating repositories for radioactive waste. Its half-life and chemical mobility force the search for special matrices for reliable insulation.
Today, tecnecium remains a niche but extremely important element in diagnostic medicine. However, its potential is broader. Tecnecium is a promising material for making catalysts (for example, for the dehydration of organic compounds) and components of high-temperature superconducting alloys. Also, chemists are developing methods for separating tecnecium from liquid radioactive waste using sorbents and new compounds for targeted nuclear medicine, including theranostics (diagnosis and therapy with one molecule).
In the future, it is possible that new methods of extracting Tc-99m from reactor and accelerator accumulations will appear, making diagnosis even more accessible. Also promising is the use of the isotope Tc-99 in nuclear batteries for devices that work for decades without recharging.
Conclusion: 43rd element of the periodic system — a bridge between the predictive genius of the 19th century and the high technologies of the 21st century. Tecnecium, the first artificial element without stable isotopes, is the only metal that is used in millions of medical diagnoses every year in the form of the isomer Tc-99m.
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