There is a cell under number 43 in the periodic table of Dmitry Ivanovich Mendeleev. For many years it remained empty. Its inhabitant did not yield 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 have survived 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.
Technetium 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, it contained 63 elements and several empty spaces. 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 declarations of 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 Segrè worked in the United States, in the laboratory of Ernest Lawrence — the inventor of the cyclotron. Segrè 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 carried out a series of complex chemical operations. They managed to isolate the new radioactive element in pure, albeit microscopic, quantities.
Technetium is the lightest element in the periodic table without 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. Technetium is a silver-gray transition metal. Its crystal lattice at standard conditions is hexagonal, it is malleable and ductile. Surprisingly, at low temperatures, technetium becomes a superconductor.
Chemical versatility. Technetium has oxidation states from −1 to +7, and the most stable form is the seven-valent technetium (Tc7+). At the same time, chemists often compare it to rhenium. This versatility creates serious problems in the processing of spent nuclear fuel: unpredictable redox reactions involving technetium complicate the processes of uranium and plutonium separation.
Today, the majority of technetium is extracted from the waste of the nuclear industry — from spent fuel rods of nuclear reactors. The yield of the isotope Tc-99 during uranium-235 fission 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. Radiopharmaceuticals for diagnosing malignant tumors, assessing blood flow in the heart, and studying the functions of many internal organs are produced on its basis. The mechanism is such: Tc-99m emits gamma rays that are easily detectable 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 inflammatory focus, or an area of myocardial ischemia.
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 technetium-99m are performed worldwide every year. In Russia, the production of technetium-99m generators is carried out by enterprises of the scientific division of "Rosatom".
The long-lived technetium-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 in the creation of repositories for radioactive waste. Its half-life and chemical mobility force the search for special matrices for reliable insulation.
Today, technetium remains a niche but extremely important element in diagnostic medicine. However, its potential is broader. Technetium is a promising material for making catalysts (for example, for the dehydrogenation of organic compounds) and components of high-temperature superconducting alloys. Also, chemists are developing methods for capturing technetium 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 residues will appear, making diagnosis even more accessible. Also promising is the use of the isotope Tc-99 in nuclear batteries for devices that operate for decades without recharging.
Conclusion: The 43rd element of the periodic system is a bridge between the predictive genius of the 19th century and the high technologies of the 21st century. Technetium, the first artificial element without stable isotopes, is the only metal that is used in millions of medical diagnostics every year in the form of the isomer Tc-99m.
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