What Is Technetium?

Technetium is a chemical element with atomic number 43 and symbol Tc, distinguished as the lightest element in the periodic table that has no stable isotopes. All of its known forms are radioactive, a property that makes technetium absent from the natural environment except in trace quantities produced by spontaneous fission of uranium and neutron capture in molybdenum ores. The element was first produced artificially in 1937 by Carlo Perrier and Emilio Segrè through bombardment of a molybdenum target with deuterons in a cyclotron at the University of California, Berkeley, making it the first element to be created rather than discovered in nature. Its name derives from the Greek tekhnetos, meaning artificial.

Technetium occupies group 7 of the periodic table alongside manganese and rhenium, sharing their chemistry as a transition metal capable of multiple oxidation states. Despite its radioactivity, technetium has substantial technological importance, particularly in nuclear medicine, where one of its metastable isomers is the most widely used radioisotope in diagnostic imaging worldwide.

Discovery and Nuclear Properties

Technetium has no stable isotope; all 43 of its known isotopes decay by beta emission, electron capture, or isomeric transition. The most long-lived isotopes are technetium-97 (half-life 4.21 million years), technetium-98 (4.2 million years), and technetium-99 (211,100 years). The long half-life of technetium-99 has implications for nuclear waste management, as it is a significant fission product of uranium-235 and plutonium-239 in reactor fuel, contributing to the long-term radiotoxicity of spent fuel. Technetium-99 is also recognized by the U.S. National Institute of Standards and Technology (NIST) as a standard beta-emitter reference material used for calibrating radiation detection equipment.

In the nuclear chart, technetium-99m (99mTc) is a metastable nuclear isomer of technetium-99, lying 142.7 keV above the ground state. It decays by isomeric transition, emitting a 140.5 keV gamma ray with a half-life of approximately 6 hours before converting to technetium-99. This combination of gamma energy and half-life is near-ideal for gamma camera and SPECT (single-photon emission computed tomography) imaging.

Production and Supply Chain

Technetium-99m is produced in nuclear reactors by neutron irradiation of molybdenum-98, converting it to molybdenum-99 (half-life 66 hours), which then decays to technetium-99m. The molybdenum-99 is loaded into technetium generators, portable devices that allow hospital radiopharmacies to elute (wash out) technetium-99m on demand throughout the generator's useful life of approximately one week. This supply chain requires a continuous flow of reactor-produced molybdenum-99 from a small number of high-flux research reactors worldwide. The NCBI Bookshelf report on molybdenum-99 and technetium-99m supply documents the international logistics that sustain the global supply of this critical medical isotope.

Medical and Radiopharmaceutical Use

Technetium-99m is FDA-approved for diagnostic imaging of more than a dozen organ systems, including brain, bone, lungs, kidneys, thyroid, heart, liver, spleen, and lymph nodes. Its short half-life limits patient radiation dose while its 140.5 keV gamma ray is efficiently detected by scintillation cameras. Radiopharmaceuticals are formed by attaching technetium-99m to organ-specific carrier molecules: methylene diphosphonate (MDP) for bone scans, sestamibi for cardiac perfusion imaging, and macroaggregated albumin (MAA) for lung perfusion studies, among many others. With tens of millions of procedures performed annually, technetium-99m accounts for approximately 80 percent of all nuclear medicine diagnostic procedures, as documented in NIH's clinical overview of technetium-99m.

Applications

Technetium has applications in a range of fields, including:

• Nuclear medicine bone, cardiac, renal, and thyroid diagnostic imaging
• Sentinel lymph node mapping in cancer surgery
• Radiation detector calibration as a NIST-standard beta emitter
• Nuclear waste characterization and spent fuel management
• Corrosion inhibitor research for steel in controlled laboratory settings
• Tracer studies in geochemical and environmental radioactivity research