Technetium-99
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| Technetium-99 | |
|---|---|
| Background | #faa |
| Caption | A technetium-99m generator, used to produce the metastable isomer for medical imaging. |
| Mass number | 99 |
| Num neutrons | 56 |
| Num protons | 43 |
| Halflife | 2.111e5 years |
| Decay mode1 | Beta decay |
| Decay energy1 | 0.294 MeV |
| Decay product1 | Ruthenium-99 |
| Parent | Molybdenum-99 |
| Parent decay | β− |
Technetium-99 is a significant radioisotope of the element technetium, notable for its long half-life and role as a major fission product. It is produced in substantial quantities from the nuclear fission of uranium-235 and plutonium-239 in nuclear reactors and is a primary component of long-lived radioactive waste. While the metastable isomer technetium-99m is renowned in nuclear medicine, technetium-99 itself finds important applications in industrial radiography and as a tracer in environmental science.
Properties
Technetium-99 is a pure beta emitter, decaying with a half-life of approximately 211,100 years to stable ruthenium-99. Its decay energy is relatively low, emitting beta particles with a maximum energy of 0.294 MeV. Unlike its isomer technetium-99m, it does not emit significant gamma rays, making its radiation easier to shield with materials like plastic or thin sheets of aluminum. The isotope is a metallic transition element and can form various chemical compounds, including the soluble pertechnetate anion, which influences its environmental mobility. Its long half-life and specific decay chain make it a key subject in studies of nuclear chemistry and long-term radioactive decay processes.
Production
The primary source of technetium-99 is as a fission product in nuclear fuel within nuclear power plants and during detonations of nuclear weapons. It is generated from the beta decay of its short-lived precursor, molybdenum-99, which has a half-life of about 66 hours. Most medical technetium-99m is obtained from molybdenum-99 produced in research reactors like the NRU Reactor in Canada or the High Flux Reactor in the Netherlands. Technetium-99 is also extracted during the reprocessing of spent nuclear fuel at facilities such as the Sellafield site in the United Kingdom and the La Hague site in France. The fission yield from uranium-235 is notably high, making it one of the most abundant medium-lived fission products.
Medical applications
While not used directly in diagnostic procedures, technetium-99 is intrinsically linked to medical imaging through its parent isotope, molybdenum-99. The decay of molybdenum-99 produces technetium-99m, which is the workhorse of single-photon emission computed tomography (SPECT) imaging worldwide. Devices called technetium-99m generators, often supplied by companies like Curium and Lantheus Medical Imaging, allow hospitals to elute the short-lived technetium-99m for tagging with pharmaceutical compounds such as sestamibi and medronate. The widespread use of these radiopharmaceuticals for imaging the heart, bones, and thyroid is a direct consequence of the technetium-99 decay chain.
Industrial and research uses
In industry, technetium-99 serves as a durable radioactive tracer due to its long half-life and chemical properties. It is employed in radiography to inspect welds and castings for defects in sectors like aerospace and petroleum refining. Research applications include its use as a beta radiation standard in laboratory calibration and in studies of corrosion inhibition for steel alloys. Scientists at institutions like the CERN and the Joint Institute for Nuclear Research have also investigated its nuclear structure. Furthermore, its behavior in geological formations is studied for assessing the safety of deep geological repositories for nuclear waste.
Environmental and safety considerations
Technetium-99 is a major concern in the management of high-level waste from the nuclear industry due to its long half-life and high environmental mobility, particularly in the form of water-soluble pertechnetate. It has been detected in ecosystems near nuclear facilities, such as the Irish Sea from Sellafield discharges and the Columbia River downstream from the Hanford Site. Its potential bioavailability and long-term radiological impact are subjects of ongoing assessment by agencies like the International Atomic Energy Agency and the United States Environmental Protection Agency. Handling requires strict radiation protection protocols to prevent internal contamination, though its low-energy beta emission poses an external hazard only to unprotected skin.
Category:Technetium Category:Isotopes Category:Nuclear medicine Category:Fission products