Technetium isotopes

Technetium isotopes also help tremendously in the diagnosis of breast cancer. A technetium complex preferentially binds to cancer cells, so if a patient has cancer, radioactivity imaging will reveal high levels of radioactivity from the cancerous tissues. The red spot in the image below marks the location of cancerous cells. 

Chemical elements including technetium are being produced in nuclear reactions occurring in the stars today. This has been proved by observing of the presence of technetium in some stars [1]. Technetium has no stable isotopes and none of the technetium isotopes has a half-life long enough to survive the age of the universe. So the technetium observed must have been synthesized by nuclear processes in the stars. 

Wie schon besprochen, kamen fur das Technetium als Element mit ungerader Ordnungszahl nur die Massenzahlen 97 und 99 als stabile Isotope in Betracht. Die MATTAUCHsche Regel hat aber zur Folge, daB auch diese beiden Isotope instabil sein miissen, so daB kein stabiles Technetium-Isotop existieren kann. Im Laufe der Jahre sind zahlreiche Technetium-Isotope synthetisiert worden (s. Tabelle 7). Betrachten wir zunachst die schwereren Isotope Tc 99, Tc 99, TclOl, Tc 105 und Tc 107 kommen unter den Spaltprodukten des Urans vor. 

Abb. 3- - Zerfallsencrgien der Technetium - Isotope in Abhanfigkcit ihrer Massenzahlen. 

Technetium isotopes formed upon irradiation of a molybdenum target by protons with an energy of 22 MeV have been ascertained by mass spectrometry. After separation of technetium by ion exchange, the isotopes Tc (0.5 %), Tc (56.0%), Tc (17.3%) and Tc (26.7%) are detected. The sensitivity of this method is very high 5 x 10 g of technetium can be detected. Mass spectrometric determination of technetium is also described by Kukavadze et al. . Pertech-netate is reduced to technetium metal and Tc ions are produced at 1600 to 1800 °C. 

The major characteristic of technetium is that it is the only element within the 29 transition metal-to-nonmetal elements that is artificially produced as a uranium-fission product in nuclear power plants. It is also the tightest (in atomic weight) of all elements with no stable isotopes. Since all of technetiums isotopes emit harmful radiation, they are stored for some time before being processed by solvent extraction and ion-exchange techniques. The two long-lived radioactive isotopes, Tc-98 and Tc-99, are relatively safe to handle in a well-equipped laboratory. 

Over the last few years the number of complexes with heterocyclic carbene ligands has rapidly increased. Next to complexes of all transition metals [1, 2, 9, 73, 74], NHCs have been used as ligands for more exotic metals such as the /-block elements [92] and various technetium isotopes [93]. The search for NHC complexes is still driven by the need for new and selective catalysts [94]. 

For work with solutions, and in particular with solid materials, precautions against electrostatic charging and the effects of air currents have to be taken, and standard radiochemical techniques should be used. The handling techniques required for other technetium isotopes such as Tc are described below (Scheme 2). 

Technetium isotopes are prepared by bombardment of molybdenum with protons and neutrons. A few nuclear reactions are shown for the three long-... 

Technetium can be measured by spectrophotmetric methods. It forms two characteristic peaks with absorption maxima at 247 and 285 nm. Also, it can be measured by polarographic methods. All technetium isotopes are radioactive. The element can be identified from its specific activity using a scintillation counter. 

The technetium isotope produced is the metastable "mTc, which is in a nuclear excited state. The eventual fall to the ground state has a half-life of 6 hours, and is accompanied by the emission of a gamma-ray photon. The gamma-ray photons have energies sufficiently low not to harm... 

One of the strangest transition metals in modern medicine is technetium, which does not exist on Earth naturally. Its half-life, or the time that it takes for half of a sample of the element to break down, is so short that all the technetium created when the Earth formed has already disappeared. But scientists have found a way to bring it back from the dead. When an isotope of the element molybdenum—another transition metal—breaks down, it turns into an isotope of technetium that lasts for about 6 hours. The technetium isotope latches on to certain kinds of heart muscle and can be seen in the muscle with special machines, similar to an X-ray. 

Doctors sometimes inject the technetium isotope to help them see exactly where a heart has been damaged after a heart attack... 

The technetium isotope of interest for nuclear fuel waste disposal is Tc. It is a pure 3-emitter (E = 0.293 MeV) with a half-life of 2.13x10 years. Its high fission yield of 6% accounts for the relatively high concentration 0.02% by weight) (1) in fuel discharged from a CANDU (CANada Deuterium Uranium) reactor (burnup 650 GJ/kg U). 

Technetium Isotopes. NH, cO, half-life 61 days), obtained from New England Nuclear, and NH TcO, from Amersham-Searle, were used in this study. The presence of reduced technetium was determined by extracting the Tc(7+) into... 

Short-lived technetium Isotopes, produced as a daughter product of molybdenum radioisotopes or as fission products of U255 were extracted as the tetraphenylarsonlum salt In chloroform together with perrhenate carrier (91,262). 

Rdsch F, Qaim SM (1993) Nuclear data relevant to the production of the positron emitting technetium isotope " Tc via the Mo(p,n)-reaction. Radiochim Acta 62 115-121 Rdsch F, Novgorodov AF, Qaim SM (1994) Thermochromatographic separation of Tc from enriched molybdenum targets and its large scale production for nuclear medical application. Radiochim Acta 64 113-120... 

Klement 43 in the seventh subgroup of the periodic system, technetium, is the lowest atomic number radioelement. Stable, non-radioactive isotopes do not exist according to Mattauch s rule. Technetium isotopes can be produced artificially by nuclear processes. Long-lived isotopes are Tc (2.6 10 a), Tc (4.2 10 a) and Tc (2.1 10- a). The spectroscopic discovery of technetium in several fixed stars provided the first proof of stellar synthesis of heavy nuclides. Traces of Tc occur in the earth s crust where they arise mainly from spontaneous fission of... 

Among the long-lived technetium isotopes only the p -emitter Tc with a half-life of 2.13-10 a is obtained in vveighablc amounts, either by neutron irradiation of highly purified natural molybdenum or by induced fission of with thermal neutrons. Because of the high fission yield of 6.13 atom%, appreciable quantities of Te ean be isolated from uranium fission product mixtures. Nuelear reactors with a power of 3500 MWth produce about 100 g of Tc per day or 6 TBq ( 10 kg) c/GWn, per year. 

Fig. 5.1.A A modified section of the nuclide churt of some technetium isotopes and isolopes of rullie-niuni and molybdenum. The stable isotopes are indicated by tlie hatched sejuares.

Small quantities (f.ig) of the three long-lived technetium isotopes Tc. and Tc were produced for the first lime by bombarding molybdenum metal with 22 VIeV protons [8. Small amounts of Te are also accessible by neutron irradiation of ruthenium... 

Among the technetium isotopes, only " Tc, a pure emitter ( ,nax=0.29 McV) with a half-life of 213 000 a, can be obtained (Sect. 5.1) in amounts adequate for studying the technical applicability of the element and its compounds. However, the widespread use of technetium is necessarily restricted by its radioactivity. The application of the metastable isotope Tc in nuclear medicine has quite superior significance and will be described in detail in Part B. 

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