Technetium-99m is produced through the radioactive decay of molybdenum-99, which itself is created inside nuclear reactors by splitting uranium-235. The process involves a carefully orchestrated chain: reactor irradiation, chemical extraction, shipping, and finally a bedside generator that delivers the finished isotope to hospitals on demand. With a half-life of only 6 hours, technetium-99m cannot be manufactured in advance and stored, making its production one of the most time-sensitive supply chains in modern medicine.
Step One: Making Molybdenum-99 in a Reactor
The process starts with uranium-235 targets placed inside a research nuclear reactor. When neutrons strike these targets, the uranium atoms split apart in a process called fission. That fission produces dozens of different byproducts, and about 6.1 percent of the time, one of those byproducts is molybdenum-99. Uranium-235 has an exceptionally high probability of absorbing a neutron and splitting, which is why it remains the preferred starting material.
After irradiation, the targets are removed from the reactor and dissolved in chemical solutions to separate molybdenum-99 from the other fission products. This extraction must happen quickly because molybdenum-99 has a half-life of roughly 66 hours, meaning it loses half its useful radioactivity every two and a half days. The purified molybdenum-99 is then loaded into generators and shipped to hospitals and pharmacies around the world.
Only a handful of aging research reactors supply most of the world’s molybdenum-99. The most important have historically been the NRU reactor in Canada, the High Flux Reactor in the Netherlands, the BR2 in Belgium, OSIRIS in France, and the SAFARI reactor in South Africa. Several of these reactors are over 50 years old, which has raised ongoing concerns about supply reliability. Because molybdenum-99 cannot be stockpiled, any unplanned reactor shutdown can cause immediate shortages at hospitals.
The Generator: A Portable Isotope Factory
The device that actually delivers technetium-99m to hospitals is called a molybdenum-99/technetium-99m generator, sometimes nicknamed a “moly cow” because technicians repeatedly “milk” it for doses. It is a small, shielded canister containing a column of aluminum oxide loaded with molybdenum-99. The molybdenum atoms stick to the aluminum through electrostatic attraction: the molybdenum carries a negative charge, while the aluminum surface is positively charged at the acidic conditions used during manufacturing.
As molybdenum-99 decays, it transforms into technetium-99m. To collect it, a technician passes a simple saline solution (0.9% sodium chloride) through the column. The technetium washes off the aluminum in a chemical form called pertechnetate, while the molybdenum stays behind, continuing to generate fresh technetium-99m. This process, called elution, can be repeated multiple times over about a week before the molybdenum-99 has decayed too much to produce useful quantities.
The elegance of this system is that it puts isotope production directly in the hospital. No second shipment is needed. A generator arrives by courier, sits in the nuclear medicine department, and produces fresh technetium-99m on demand for days.
Why Technetium-99m Works So Well for Imaging
When technetium-99m decays into technetium-99, it releases a gamma ray with an energy of 140 keV. That energy level is ideal for medical imaging cameras: high enough to pass through body tissue and reach the detector, but low enough that the radiation dose to the patient stays relatively small. The 6-hour half-life is also a practical sweet spot. It is long enough for a technician to prepare the dose, inject the patient, and complete the scan, but short enough that the radioactivity fades quickly afterward. The final decay product, technetium-99, is only very weakly radioactive with a half-life of about 214,000 years, meaning it emits radiation at an extremely low rate and poses negligible risk.
The Race Against Decay
The 66-hour half-life of molybdenum-99 turns the entire supply chain into a logistics challenge. From the moment the uranium target comes out of the reactor, the clock is ticking. The target must be chemically processed, the molybdenum-99 purified, generators assembled, and packages shipped to hospitals, often across international borders. By the time a generator reaches a nuclear medicine department, a significant fraction of the original molybdenum-99 has already decayed away. Every day of delay means less technetium-99m available for patients.
This is why production runs continuously. Reactors irradiate new targets on a weekly cycle, processing facilities operate around the clock, and generators are shipped by air freight on tight schedules. There is no buffer of stored inventory anywhere in this chain.
The Shift From Highly Enriched Uranium
Historically, most molybdenum-99 was produced using highly enriched uranium (HEU) targets, the same type of uranium used in nuclear weapons. This created a proliferation concern: shipments of weapons-grade material moving regularly between countries. An international effort has been underway for years to switch production to low-enriched uranium (LEU) targets instead. Nearly all molybdenum-99 suppliers outside of Russia have either completed this conversion or are in the final stages of doing so.
Cyclotron Production: Skipping the Reactor
A newer approach bypasses the reactor and generator system entirely by making technetium-99m directly using a particle accelerator called a cyclotron. In this method, a beam of protons is fired at a target made of molybdenum-100 (a different, stable isotope of molybdenum). The proton strikes the molybdenum-100 nucleus, knocking out two neutrons and converting it directly into technetium-99m. The optimal proton energy for this reaction falls between 10 and 22 million electron volts, a range achievable by the medical cyclotrons already installed at many large hospitals for producing other imaging isotopes.
Cyclotron production has a major advantage: it can be done locally, eliminating the international shipping bottleneck. A hospital with a cyclotron could, in principle, manufacture its own technetium-99m each morning. The limitation is scale. A single cyclotron produces enough for one hospital or a small regional network, not for an entire country. Still, this approach is considered one of the most promising backup options for weathering reactor shutdowns and supply shortages.
Neutron Capture: A Simpler Reactor Method
There is also a second reactor-based approach that avoids uranium entirely. Instead of splitting uranium, a stable molybdenum-98 target is placed in a reactor and absorbs a neutron, converting it into molybdenum-99. This is simpler and produces far less radioactive waste than the fission method. The tradeoff is that the molybdenum-99 produced this way has much lower specific activity, meaning less radioactivity per gram of material. That makes it harder to load into the small generator columns hospitals are designed to use, though specially designed generators using materials like zirconium molybdate gel or nano-scale aluminum oxide can partially compensate.
The fission process also co-produces other medically useful isotopes, including iodine-131 and xenon-133. Switching entirely to neutron capture would require finding separate sources for those isotopes as well.