Technetium

Technetium. It is the lightest element whose isotopes are all radioactive, with none being stable. The discovery of this element filled a notable gap in the periodic table, specifically within the d-block between molybdenum and ruthenium. Its most common isotope, technetium-99m, is a crucial metastable nuclear isomer widely employed in medical imaging procedures around the world.

Properties

In its pure form, it is a silvery-gray, crystalline metal that tarnishes slowly in moist air. Chemically, its properties are intermediate between those of its neighbors manganese and rhenium in group 7. It exhibits a wide range of oxidation states, with the most stable being +4 and +7 in compounds like technetium dioxide and potassium pertechnetate. The element is a weak superconductor at very low temperatures, a property studied in facilities like the National Institute of Standards and Technology. Its chemistry is dominated by the +7 state, which forms the stable, water-soluble pertechnetate anion, analogous to permanganate.

History

The existence of an element with atomic number 43 was predicted by Dmitri Mendeleev, who provisionally named it eka-manganese. Early claims of discovery, such as ilmenium by the Russian chemist R. Hermann and later masurium by Walter Noddack, Ida Tacke, and Otto Berg, were not substantiated. The element was first conclusively identified in 1937 by Carlo Perrier and Emilio Segrè at the University of Palermo in Sicily, who isolated it from a sample of molybdenum bombarded with deuterons in the cyclotron at the University of California, Berkeley. They named it after the Greek word *τεχνητός* (technetos), meaning "artificial."

Occurrence and production

Naturally occurring on Earth only in minute traces from the spontaneous fission of uranium-238 or neutron capture in molybdenum ores, it is primarily an artificial element. The majority is produced as a fission product in nuclear reactors from the nuclear fission of uranium-235 or plutonium-239. The isotope technetium-99 is a major component of nuclear waste. The medically vital technetium-99m is typically obtained from the decay of its parent isotope, molybdenum-99, which is produced in reactors like the NRU reactor in Canada or the High Flux Reactor in the Netherlands.

Applications

Its primary application is in nuclear medicine, where technetium-99m is used in over 80% of all diagnostic imaging procedures, including single-photon emission computed tomography (SPECT) scans to examine the heart, brain, and skeletal system. The radiopharmaceutical sestamibi is a key agent for myocardial perfusion imaging. Beyond medicine, technetium-99 serves as a versatile radioactive tracer in industrial radiography to check for flaws in metal welds and structures. In research, certain alloys containing the element have been investigated for their corrosion resistance properties in extreme environments.

Precautions

All isotopes require careful handling as radioactive materials, governed by agencies like the International Atomic Energy Agency and the Nuclear Regulatory Commission. Technetium-99, with a long half-life of over 200,000 years, is a significant environmental concern due to its mobility as pertechnetate in groundwater, posing challenges for long-term storage at sites like the Hanford Site. In medical use, the short half-life of technetium-99m minimizes patient radiation dose, but strict protocols from institutions like the Society of Nuclear Medicine and Molecular Imaging ensure safe preparation and administration by trained personnel.

Category:Chemical elements Category:Transition metals Category:Synthetic elements