Technetium
Many of technetium's properties were predicted by Dmitri Mendeleev before the element was discovered. Mendeleev noted a gap in his periodic table and gave the undiscovered element the provisional name ekamanganese (Em). In 1937, technetium (specifically the technetium-97 isotope) became the first predominantly artificial element to be produced, hence its name (from the Greek meaning "artificial").
Its short-lived gamma ray-emitting nuclear isomer—technetium-99m—is used in nuclear medicine for a wide variety of diagnostic tests. Technetium-99 is used as a gamma ray-free source of beta particles. Long-lived technetium isotopes produced commercially are by-products of fission of uranium-235 in nuclear reactors and are extracted from nuclear fuel rods. Because no isotope of technetium has a half-life longer than 4.2 million years (technetium-98), its detection in 1952 in red giants, which are billions of years old, helped bolster the theory that stars can produce heavier elements.
Occurrence and production
Only minute traces occur naturally in the Earth's crust as a spontaneous fission product in uranium ores. A kilogram of uranium contains an estimated 1 nanogram (10−9 g) of technetium. Some red giant stars with the spectral types S-, M-, and N contain an absorption line in their spectrum indicating the presence of technetium. These red-giants are known informally as technetium stars.
Fission waste product
In contrast with its rare natural occurrence, bulk quantities of technetium-99 are produced each year from spent nuclear fuel rods, which contain various fission products. The fission of a gram of uranium-235 in nuclear reactors yields 27 mg of technetium-99, giving technetium a fission product yield of 6.1%. Other fissile isotopes also produce similar yields of technetium, such as 4.9% from uranium-233 and 6.21% from plutonium-239. About 49,000 TBq (78 metric tons) of technetium is estimated to have been produced in nuclear reactors between 1983 and 1994, which is by far the dominant source of terrestrial technetium. Only a fraction of the production is used commercially.
Technetium-99 is produced by the nuclear fission of both uranium-235 and plutonium-239. It is therefore present in radioactive waste and in the nuclear fallout of fission bomb explosions. Its decay, measured in becquerels per amount of spent fuel, is dominant after about 104 to 106 years after the creation of the nuclear waste. From 1945 to 1994, an estimated 160 TBq (about 250 kg) of technetium-99 was released into the environment by atmospheric nuclear tests. The amount of technetium-99 from nuclear reactors released into the environment up to 1986 is on the order of 1000 TBq (about 1600 kg), primarily by nuclear fuel reprocessing; most of this was discharged into the sea. Reprocessing methods have reduced emissions since then, but as of 2005 the primary release of technetium-99 into the environment is by the Sellafield plant, which released an estimated 550 TBq (about 900 kg) from 1995–1999 into the Irish Sea. From 2000 onwards the amount has been limited by regulation to 90 TBq (about 140 kg) per year. Discharge of technetium into the sea has resulted in some seafood containing minuscule quantities of this element. For example, European lobster and fish from west Cumbria contain about 1 Bq/kg of technetium.
| Symbol | Tc | |
| Atomic Number | 43 | |
| Atomic Weight | 97.9072 | |
| Oxidation States | +4,+6,+7 | |
| Electronegativity, Pauling | 1.9 | |
| State at RT | Solid, Metal | |
| Melting Point, K | 2445 | |
| Boiling Point, K | 5150 |
Appearance and Characteristics
Harmful effects:
Technetium is harmful due to its radioactivity.
Characteristics:
- Technetium is a rare, silver-gray metal that tarnishes slowly in moist air.
- In powder form, it burns in oxygen to the heptoxide (Tc2O7).
- Technetium dissolves in nitric acid and concentrated sulfuric acid, but is not soluble in hydrochloric acid of any strength.
- Is an excellent superconductor at temperatures of 11 K and below.
- Technetium and promethium are unusual among the light elements, because they have no stable isotopes.
Uses of Technetium
- Technetium-99m is a metastable isotope with a half-life of six hours. Technetium-99m emits gamma rays and low energy electrons, forming technetium-99 (half-life 211 000 years). The gamma rays can be photographed using a gamma camera, and technetium-99m is used in 80 to 90 percent of all diagnostic procedures that use radioactive elements.
- Technetium-95, with a half-life of 61 days, is used as a radioactive tracer.
- Technetium-99, has a very long half-life (2.11 X 105 years) and decays almost entirely by beta decay with no gamma rays. It is used as for equipment calibration.
- In small concentrations the pertechnetate ion (TcO 4-) can protect carbon steels and iron from corrosion. This use is limited to closed systems due to its radioactivity.
