Technetium half-life

Several modes of waste management are available. The simplest is to dilute and disperse. This practice is adequate for the release of small amounts of radioactive material to the atmosphere or to a large body of water. Noble gases and slightly contaminated water from reactor operation are eligible for such treatment. A second technique is to hold the material for decay. This is appHcable to radionucHdes of short half-life such as the medical isotope technetium-9 9m = 6 h), the concentration of which becomes negligible in a week s holding period. The third and most common approach to waste... 

Technetium-99m (the m signifies a metastable, or moderately stable, species) is generated in nuclear reactors and shipped to hospitals for use in medical imaging. The radioisotope has a half-life of 6.01 h. If a 165-mg sample of technetium-99m is shipped from a nuclear reactor to a hospital 125 kilometers away in a truck that averages 50.0 kmh. what mass of technetium-99m will remain when it arrives at the hospital ... 

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. 

Although the half-life of "Tc in steller interiors is remarkably decreased, a substantial amount of the isotope ean survive the s-process. Observations have revealed that more than 50 stars contain technetium in their outer envelope. According to other calculations, the production of neutrons in the competitive processes of neutron capture and / -decay is even more enhanced at such high temperatures, and this fact almost compensates for the depletion of "Tc [41]. 

Transfer of technetium from seawater to animals has been studied by laboratory experiments using 95mTc, The advantages of 95mTc over "Tc are 95mTc emits y-rays, thus whole-body counting techniques can be used, and it has a sufficiently high specific activity because of its relatively short half life (61 d). 

TEA chloride See tetraethylammonium chloride., te,e a klorjd ) technetium chem A transition element, symbol Tc, atomic number 43 derived from uranium and plutonium fission products chemically similar to rhenium and manganese isotope Tc has a half-life of 200,000 years used to absorb slow neutrons in reactor technology. tek ne-she-om ... 

Most radioactive nuclides employed in radiopharmaceuticals have a short half-life. This is beneficial to the patient as the total number of radioactive atoms given to the patient to produce an image is small when the half-life of the radioactive nuelide is short, as compared to longer half-life radioactive nuclides. Fewer total atoms reduce the radiation dose to the patient and thus the risk from a nuclear medi-eine procedure. However, the short half-life of the radioactive nuclide results in a short shelf-life for the radiopharmaeeutical. As a result, most radiopharmaceuticals are eompounded on a daily basis. The most common radioactive nuclide used for this purpose is technetium-99m (Te-99m) with a half-life of 6 hr, emiting only gamma radiation with an energy almost ideal for detection. 

The most sensitive method for determining trace amounts of technetium is the neutron activation . The Tc sample is irradiated by slow neutrons. The radioactive isotope Tc with a half-life of 15.8 s is formed by the reaction Tcfn, y) Tc, the neutron capture cross section of which is comparatively large (20 bams), so that it is possible to determine amounts < 2x 10 " g of Tc. However, the method is not widely used since the half-life of Tc is very short. Moreover, this method is only convenient when a reactor or a neutron source is available. 

It was the first new element to be produced artificially from another element experimentally in a laboratory. Today, all technetium is produced mostly in the nuclear reactors of electrical generation power plants. Molybdenum-98 is bombarded with neutrons, which then becomes molybdenum-99 when it captures a neutron. Since Mo-99 has a short half-life of about 66 hours, it decays into Tc-99 by beta decay. 

The major driving force for the development of technetium coordination chemistry has undoubtedly been the potential applications in diagnostic nuclear medicine. The primary requirements for a radionuclide to be used in imaging are that the radiation emitted must be of appropriate energy, the decay half-life must lie in a suitable time window, it must be relatively cheap and readily available in the radiopharmacy, and finally it must have highly flexible co-ordination chemistry. 

Technetium has not been found to exist on earth. However, it has been detected in certain stars. Long-hved technetium-99 isotope of half-life 2.15x10 years is found in relatively significant quantities in fission products of uranium-235. Every Ig of uranium-235 yields about 0.027g of technetium-99 from its fission. 

There are no stable isotopes of technetium. The element is obtained from fission reactions rather than from natural sources. The most commonly encountered isotopes are Tc, a weak 292-keV emitter with a half-life of 2.1 x 10 yr, and Tc, a metastable form that decays to Tc with the emission of a 140-keV y photon with a half-life of ca 6 h. The coordination chemistry [1, 2] and electrochemistry [3] of technetium have been reviewed on several occasions. 

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... 

The first member of this family, manganese, exhibits One of the most interesting redox chemistries known thus it has already been discussed in detail above. Technetium exhibits the expected oxidation states, and associated with these are modest emf values. All of the isotopes of technetium are radioactive but "Tc has a relatively long half-life (2.14 k 10s years) and is found in nature in small amounts because of the radioactive decay of uranium. Oxidation slates of rhenium range from +7 to - 3, with some species ReOj and Re3+) unstable with respect to disproportionation. 

The radioisotope most widely used today is technetium-99m, whose short half-life of 6.01 hours minimizes a patient s exposure to harmful effects. Bone scans using Tc-99m, such as that shown in Figure 22.12a, are an important tool in the diagnosis of cancer and other pathological conditions. 

I (radioactive half-life 13 hours) has replaced 131I for diagnostic purposes however, for in vivo imaging meta-stable technetium-99 (99mTc) is often preferred, because of its lower radiation dose, availability, and cost. 

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