Technetium is a chemical element; it has symbol Tc and atomic number 43. It is the lightest element whose isotopes are all radioactive.
Many of technetium’s properties had been predicted by Dmitri Mendeleev before it was discovered; Mendeleev noted a gap in his periodic table and gave the undiscovered element the provisional name ekamanganese (Em).
In 1937, technetium became the first predominantly artificial element to be produced, hence its name (from the Greek technetos, ‘artificial’, + -ium).
Because even the longest-lived isotope of technetium has a relatively short half-life (4.21 million years), the 1952 detection of technetium in red giants helped to prove that stars can produce heavier elements.
[Emilio] Segrè enlisted his colleague Perrier to attempt to prove, through comparative chemistry, that the molybdenum activity was indeed from an element with the atomic number 43, which they did. … In 1947, element 43 was named after the Greek word technetos (τεχνητός), meaning ‘artificial’, since it was the first element to be artificially produced. Segrè returned to Berkeley and met Glenn T. Seaborg. They isolated the metastable isotope technetium-99m, which is now used in some ten million medical diagnostic procedures annually.
In 1952, the astronomer Paul W. Merrill detected the spectral signature of technetium (specifically wavelengths of 403.1 nm, 423.8 nm, 426.2 nm, and 429.7 nm) in light from S-type red giants. The stars were near the end of their lives but were rich in the short-lived element, which indicated that it was being produced in the stars by nuclear reactions. That evidence bolstered the hypothesis that heavier elements are the product of nucleosynthesis in stars.
In 1962, technetium-99 was isolated and identified in pitchblende from the Belgian Congo in very small quantities (about 0.2 ng/kg), where it originates as a spontaneous fission product of uranium-238.
The most stable radioactive isotopes are technetium-97 with a half-life of 4.21±0.16 million years and technetium-98 with 4.2±0.3 million years…. Thirty-four other radioisotopes have been characterized with mass numbers ranging from 86 to 122. Most of these have half-lives that are less than an hour, the exceptions being technetium-93 (2.75 hours), technetium-94 (4.88 hours), technetium-95 (19.26 hours), and technetium-96 (4.28 days).
Technetium occurs naturally in the Earth’s crust in minute concentrations of about 0.003 parts per trillion. Technetium is so rare because the half-lives of 97Tc and 98Tc are only 4.2 million years. More than a thousand of such periods have passed since the formation of the Earth.
echnetium-99 electroplated onto a strip of gold foil By GFDL, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=109512161
Simulated emission spectrum of neutral Technetium (Tc I) based on data from the National Institute of Standards and Technology Atomic Spectra Database (NIST ASD).
Elder G walks us thru the spectral line discovery.
Technetium has no stable isotopes.
Every isotope of technetium is radioactive. The most relevant one in stars, technetium-99, has a half-life of about 211,000 years. That sounds like a long time, but in the life of a star, it’s the equivalent of finding a cup of hot coffee in a house abandoned for centuries. If it’s still warm, someone made it recently.
The mystery
In the 1950s, astronomer Paul W. Merrill examined the spectra of certain red giant stars and noticed absorption lines belonging to technetium. This was astonishing.
If these stars had simply inherited their technetium when they formed billions of years ago, every atom would have decayed long ago. There shouldn’t have been any left. Yet there it was.
The solution
The only reasonable explanation was that the stars were manufacturing technetium right now.
Inside aging red giants, neutron-capture reactions gradually build heavier and heavier elements from lighter ones. This is called the s-process (“slow neutron capture process”).
Very roughly: Iron → heavier nuclei → zirconium → molybdenum → technetium → ruthenium → …
The star “cooks” these elements deep inside. Later, enormous convective currents, called dredge-up, slowly bring some of this freshly made technetium to the surface, where astronomers can detect it in the star’s spectrum.
Artemis Spyrou and Hendrik Schatz have an interesting and very readable article in The Conversation (Academic rigor, journalistic flair) where they describe Paul Merrill’s discovery and discuss nuclear fusion in stars.
Nearly 70 years ago, astronomer Paul Merrill was watching the sky through a telescope at Mount Wilson Observatory in Pasadena, California. As he observed the light coming from a distant star, he saw signatures of the element technetium.
This was completely unexpected. Technetium has no stable forms – it’s what physicists call an “artificial” element. As Merrill himself put it with a bit of understatement, “It is surprising to find an unstable element in the stars.”
Modern nucleosynthesis experiments, like those of the authors, are run on nuclear physics equipment including particle accelerators. National Superconducting Cyclotron Laboratory, CC BY-ND
We’ve been looking to get a DIY nucleosynthesis machine.
Here’s our budget. The coffee pot is non-negotiable.
WLBOTT Home Nucleosynthesis Initiative
Item
Estimated Cost
Used particle accelerator (slightly dented)
$18,000,000
Superconducting magnets
$45,000,000
Liquid helium budget
$2,500,000/year
Radiation shielding (lead, concrete, and hope)
$12,000,000
Power substation
$25,000,000
Extension cord from garage to substation
$19.95
Industrial cooling system
$8,000,000
Coffee maker
$89
Coffee budget
$4,800/year
Replacement garage door
$2,100
Marriage counseling
Variable
Grand Total:Approximately $110 million
We asked our artist-in-residence, Perch Periwinkle (of the La Mesa Periwinkle) if she’d like to decorate the laboratory. Big Texas Yes!
Technetatia, the Goddess of Tech Support
The Greek Goddess Technetatia was based on an actual ancient Greek woman. Eternally petulant and fed up with the clueless user community, she later became deified.
Leaving No Turn Un-Stoned
And while we’re at it, “Red Giant” is ambiguous enough to get some good AI images.
Anyhow….
Medical Imaging
Technetium-99m (Tc-99m) is the most widely used radioactive tracer in medical imaging, powering roughly 80% of all nuclear medicine diagnostic procedures worldwide.
Elder G provides a nice summary.
This is actually one of technetium’s greatest success stories. While WLBOTT is busy trying to manufacture technetium in the garage, hospitals quietly use it every day to help millions of patients.
The workhorse is technetium-99m (pronounced “technetium ninety-nine m“), where the “m” stands for metastable.
Why technetium-99m is almost the perfect medical isotope
It has a remarkable combination of properties:
Half-life: about 6 hours
Long enough for doctors to perform imaging.
Short enough that most of the radioactivity disappears within a day or two.
It emits a 140 keV gamma ray, which is energetic enough to leave the body and be detected by a gamma camera, but not so energetic that it delivers unnecessary radiation.
It emits very little particulate radiation, so it provides excellent images while keeping the patient’s radiation dose relatively low.
In nuclear medicine, that’s almost the Goldilocks combination: not too long, not too short, not too energetic, not too weak.
How it’s used
The technetium isn’t injected by itself. Chemists attach it to molecules that naturally travel to specific organs.
Think of it as putting a tiny glowing beacon on a molecule the body already knows where to send.
For example:
Bone scans
Technetium attaches to phosphonate compounds.
These accumulate where bone is actively remodeling.
Useful for detecting fractures, infections, arthritis, or cancer spread.
Heart scans
Certain technetium compounds are taken up by healthy heart muscle.
Areas with poor blood flow appear dimmer.
This helps evaluate coronary artery disease.
Lung scans
Used to assess blood flow through the lungs.
Helpful when pulmonary embolism is suspected.
Brain imaging
Some compounds cross into brain tissue, allowing physicians to evaluate blood flow.
Kidneys
Different technetium compounds can measure kidney function, drainage, and blood flow.
Liver and gallbladder
HIDA scans use technetium-labeled compounds that follow the normal path of bile.
How the picture is made
After injection:
The radiopharmaceutical travels to the target organ.
The technetium emits gamma rays.
A gamma camera detects those gamma rays.
A computer reconstructs an image showing where the tracer accumulated.
Unlike an ordinary X-ray, which shows anatomy, many technetium scans reveal physiology. They show how an organ is working, not just what it looks like.
Where does the technetium come from?
Most hospitals don’t make it from scratch. Instead, they receive a device called a technetium generator, affectionately nicknamed a “moly cow.”
Inside is molybdenum-99, which decays into technetium-99m.
Each morning, the nuclear medicine technologist literally “milks” the generator by flushing saline through it, collecting fresh technetium-99m for the day’s patients.
It really is called milking the generator.
A technetium-99m generator, or colloquially a technetium cow or moly cow, is a device used to extract the metastable isotope 99mTc of technetium from a decaying sample of molybdenum-99. 99Mo has a half-life of 66 hours and can be easily transported over long distances to hospitals where its decay product technetium-99m (with a half-life of only 6 hours, inconvenient for transport) is extracted and used for a variety of nuclear medicine diagnostic procedures, where its short half-life is very useful.
Brookhaven National Laboratory, located in the hamlet[1] of Upton, New York, was instrumental in ushering in nuclear medicine. They commemorate the 60th anniversary with the background of the discovery in this article.
Brookhaven National Laboratory celebrates the 60th anniversary of Technetium-99m with a history of this major technological development.
“Brookhaven was founded in 1947 on the idea of the peaceful application of nuclear research,” said David Schyler, a scientist emeritus familiar with the history of the isotope program. Medical applications using radiation including isotopes for diagnosing disease and new forms of treatment were increasingly popular research topics.
Brookhaven Lab chemist Margaret Greene played a prominent role in the development of the original Tc-99m generator, shown here.
