Technetium radioactive decay

Technetium- 99 is produced in commercial quantities in nuclear reactors by bombarding molybdenum with large numbers of neutrons. A simplified version of the radioactive decay reaction follows ... 

An image of the human body recorded from the radioactive decay of metastable technetium-99 in the bloodstream... 

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. 

Some elements do not occur naturally, but can be synthesized. They can be produced in nuclear reactors, from collisions in particle accelerators, or can be part of the fallout from nuclear explosions. One of the elements most commonly made in nuclear reactors is technetium. Relatively large quantities are made every day for applications in nuclear medicine. Sometimes, the initial product made in an accelerator is a heavy element whose atoms have very short half-lives and undergo radioactive decay. When the atoms decay, atoms of elements lighter than the parent atoms are produced. By identifying the daughter atoms, scientists can work backward and correctly identify the parent atoms from which they came. 

Technetium is an artificial element obtained by the radioactive decay of molybdenum. Element 43, named technetium in 1947, had been discovered in 1937 by Carlo Perrier and Emilio Segre in a sample obtained from the Berkely Radiation Laboratory (now Lawrence Berkeley National Laboratory) in California (Perrier and Segre 1937, 1947). By bombarding a molybdenum strip with 8-MeV deuterons in a 37-in. cyclotron, a radioactive molybdenum species (half-life, 65 h) had been obtained which decayed by yff-emission to a short-lived isotope (half-life, 6 h) with novel properties, identified as technetium-99m (Segre and Seaborg 1938). 

Long-lived Tc atoms pose an inherent isotopic impurity that is eluted from the column and is also generated in the eluate by radioactive decay of Tc. Since the concentration of Tc in the eluate is very low, chemical effects may result when generators are not eluted at regular intervals. The total mass of technetium ( Tc + Tc) in the 24-h eluate is calculated as 6.90x10 g/37 MBq (1 mCi). (For calculation of specific activity, see Appendix A2 of this chapter)... 

Early forms of the periodic table left a gap between molybdenum and ruthenium. The missing element, technetium, does not have any stable isotopes. The longest-lived isotope of technetium is Tc. Predict the radioactive decay products for this isotope and explain why it does not exist naturally on earth. 

A variety of radiotracers are used in clinical work, the most used isotopes being technetium-99m, iodine-131, tantalum-201, xenon-133, and indium-113m. The use of technetium, Tc, dominates, since it can be made to react with many substances having specific biological behavior. Tc is obtained from an isotope generator, which is based on the radioactive decay of radioactive molybdenum, Mo. Pharmaceuticals containing Tc are usually introduced by intravenous injection. Some radiopharmaceuticals may also be introduced orally, e.g., for those containing iodine this is the common procedure. 

Most radioisotopes used in nuclear medicine are artificial. They are produced in nuclear reactors (e.g. Sr, Co), cyclotrons (e.g. C, F) or specialized generators such as a molybdenum-technetium generator. The metastable radioisotope ""Tc has a half-life of 6 hours and is important for medical imaging. It is a decay product of Mo - 2.8 days), which is itself man-made, being produced in a nuclear reactor. The radioactive decay of Mo to Tc and the much longer lived Tc is summarized below ... 

Clean-room assembly of technetium-99m generators. [ Mo04] is adsorbed on alumina in a cold kit generator, and radioactive decay produces [ c04P. 

Technetium is an unusual element. Although a d-transition element (under manganese in Group VIIB) with a small atomic number (Z = 43), it has no stable isotopes. The nucleus of every technetium isotope is radioactive and decays, or disintegrates, to give an isotope of another element. Many of the technetium isotopes decay by emitting an electron from the nucleus. 

The radioactive decay of technetium-95 is an example of positron emission. 

Often gamma emission occurs very quickly after radioactive decay. In some cases, however, an excited state has significant hfetime before it emits a gamma photon. A metastable nucleus is a nucleus in an excited state with a lifetime of at least one nanosecond (10 s). In time, the metastable nucleus decays by gamma emission. An example is metastable technetium-99, denoted which... 

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... 

In hospitals, radioisotope Mo-99, which decays into technetium-99, is given internally to cancer patients as a radioactive cocktail. Radioactive Tc-99 is absorbed by tissues of cancer patients, and then x-ray-hke radiation is used to produce pictures of the body s internal organs. 

Radioactive labels are -emitters selected on the basis of half-lives, the energies emitted, decay products, ease of labeling, availability and expense. Iodine isotopes 121,123, and 124, Indium 111, and Technetium 99 are the labels most widely used. The short half-lives of these labels (hours to days) means that radioimaging reagents are prepared immediately prior to treatment. Radioimaging of diseased tissue also provides useful information on the design of therapies that localize radioisotopes or toxins at tumor sites for therapy. 

Technetium-99m ("Tcm) is a radionuclide that finds many applications in nuclear medicine. Virtually all technetium used in nuclear medicine labs is prepared synthetically from other radioactive materials. "Tcm is produced by the (3 decay of "Mo as illustrated in the reaction below. "Mo is produced through fission of 235U or via the capture of a neutron by "Mo. 

Drake once suggested that an advanced civilization could place a technetium cloud around its star. This radioactive metal is observed on Earth only when it is produced artificially, and only weakly on the Sun, because it is short-lived and rapidly decays away. Drake estimated that aliens could mark a star using only a few hundred tons of light-absorbing substance spread around the star. 

The Group 7 metals technetium and rhenium have not been applied to the problem of oxidation chemistry to the level of their Group 6 and Group 8 counterparts. This is understandable in light of their relative scarcity. Technetium is a synthetic element, recovered as a fission by-product from uranium.3 "Tc is radioactive (/3 decay, 0.3 MeV, tv2 = 2.14 X 10s years) and its use even in the laboratory requires the appropriate safety precautions. Rhenium is not plagued by either issue, yet it is still a relatively rare element, present at only an estimated 0.001 ppm in the Earth s crust. It is... 

A radioactive isotope (radioisotope) is an unstable isotope of an element that decays into a more stable isotope of the same element. They are of great use in medicine as tracers (to help monitor particular atoms in chemical and biological reactions) for the purpose of diagnosis (such as imaging) and treatment. Iodine (-131 and -123) and Technetium-99 are used for their short half-lives. 

All the possible mass numbers between 142 and 150 are already taken by neod)Tnium (Z = 60) and samarium (Z = 62), so that no stable isotope is expected for element 61. They would all be radioactive, just as in the case of technetium (Z = 43). The Mattauch rule however was not capable of ascribing these radioactive isotopes a certain half-life. A number of uranium and thorium isotopes are also radioactive, but their half-lives are great enough so that one can still find them in nature. During that same year, in 1934, the American physicist and future Noble Prize winner, Willard Libby (1908-1980), discovered that neodymium is a (3 emitter (Libby, 1934). According to Soddy s displacement laws, this should imply that when neodymium decays, isotopes of element 61 should be formed. 

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