Technetium

Technetium is the lightest element with no stable isotopes, every single technetium atom that has ever existed was either created artificially or is a product of radioactive decay. It was the first element to be made artificially, closing a mysterious gap in the periodic table that had puzzled chemists for decades.

• Atomic Number4343 protons, 43 electrons
• Atomic Mass96.90636 u43× heavier than hydrogen
• State at Room TempSolidSolid
• Density11 g/cm³
• Melting / Boiling2156.8°C / 4264.9°C
• Discovered1937

What is Technetium?

Technetium is a radioactive transition metal in Group 7 of the periodic table, sitting below manganese. With 43 protons, it has no stable isotopes, all of them eventually decay into other elements. The most stable isotope, technetium-98, has a half-life of 4.2 million years, long on a human scale, but short enough that all the primordial technetium formed when the Earth was born has long since decayed away.

Technetium gets its name from the ancient Greek word technetos meaning artificial, chosen because it was the first element to be created artificially, by bombardment in a particle accelerator. The name was proposed by its discoverers Carlo Perrier and Emilio Segrè in 1947, though the element had been produced in 1937. The symbol Tc comes from the name. Mendeleev had predicted its existence as eka-manganese.

Fact Technetium-99m is the most widely used medical radiotracer in the world, used in approx. 85% of all nuclear medicine procedures. It has a half-life of just 6 hours, meaning it decays to nearly nothing within 24 hours, minimising radiation dose to the patient.

Where you find Technetium

In space

Technetium has been detected in certain types of ageing red giant stars, which is remarkable because any primordial technetium would have decayed long ago. Its presence means these stars are actively producing technetium in ongoing nuclear reactions, providing direct evidence of nucleosynthesis inside living stars.

On Earth

Technetium does not occur naturally on Earth in any significant quantity, any primordial technetium formed when the solar system began has completely decayed. Tiny traces are found in uranium ores, produced by spontaneous fission of uranium-238.

• Nuclear reactors. Technetium-99m is produced in large quantities from the fission of uranium-235 in nuclear reactors. Molybdenum-99 is the primary precursor used in hospitals.
• Uranium ores. Vanishingly small amounts of technetium occur naturally in uranium ores as a result of spontaneous fission.

How we use Technetium

• Medical imaging (Tc-99m).. Technetium-99m is the most widely used radioactive tracer in nuclear medicine. About 40 million medical scans worldwide each year use this short-lived isotope to image the heart, bones, liver, thyroid and brain.
• Corrosion inhibitor.. Technetium can protect steel from corrosion, but its radioactivity prevents practical use.

Did you know? The "m" in technetium-99m stands for "metastable", it is a nuclear isomer in a higher energy state that emits a gamma ray as it drops to its ground state. This gamma ray is what medical cameras detect. The extremely short half-life makes Tc-99m ideal for imaging: it decays quickly enough to minimise radiation dose, but slowly enough that images can be taken.

How it was discovered

Technetium was discovered in 1937 by Carlo Perrier and Emilio Segrè at the University of Palermo, who obtained a sample of molybdenum that had been bombarded with deuterons in the Berkeley cyclotron and found new radioactive elements within it. This confirmed the long-suspected existence of element 43. Segrè later shared the 1959 Nobel Prize in Physics (for the discovery of the antiproton).

Deeper dive: technetium chemistry and applications

The medical use of technetium-99m (Tc-99m) is one of the most important nuclear medicine applications ever developed. Tc-99m decays by isomeric transition, emitting a 140 keV gamma ray that passes cleanly through tissue and is detected by a gamma camera outside the body. The short 6-hour half-life means patients receive a manageable radiation dose. Different chemical compounds containing Tc-99m distribute to different organs: methylene diphosphonate (MDP) goes to bone, sestamibi to the heart, MAG3 to the kidneys. Each compound allows a different organ to be imaged with high sensitivity.

The supply of Tc-99m depends on a chain of only a handful of nuclear reactors worldwide that produce molybdenum-99 (Mo-99, half-life 66 hours). Mo-99 is shipped to hospital radiopharmacies, where it decays to Tc-99m on demand. Any shutdown of a major Mo-99 reactor creates immediate shortages in nuclear medicine departments worldwide, as happened dramatically in 2009-2010 when two reactors failed simultaneously.

Moving to 44 protons on the periodic table brings us to Ruthenium.