Technetium decay

The isotope molybdenum-99 is produced in large quantity as the precursor to technetium-99y, a radionucleide used in numerous medical imaging procedures such as those of bone and the heart (see Medical imaging technology). The molybdenum-99 is either recovered from the fission of uranium or made from lighter Mo isotopes by neutron capture. Typically, a Mo-99 cow consists of MoO adsorbed on a lead-shielded alumina column. The TcO formed upon the decay of Mo-99 by P-decay, = 66 h, has less affinity for the column and is eluted or milked and either used directly or appropriately chemically derivatized for the particular diagnostic test (100). 

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... 

The -y-ray photons emitted by the nuclear decay of a technetium-99 atom used in radiopharmaceuticals have an energy of 140.511 keV. Calculate the wavelength of these "y-rays. 

Technetium-99m is produced by a sequence of reactions in which molybdenum-98 is bombarded with neutrons to form molybdenum-99, which undergoes p decay to technetium-99m. 

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]. 

Occurrence. The natural abundance of Tc is negligibly small. Technetium is a by-product of the nuclear industry and it is a product of the uranium decay. 

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. 

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. 

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 ... 

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. 

Special attention has been paid to Re, since this isotope can readily be obtained from isotope generators which are based on the decay of (physical ti/2 = 69.4 d) in a matrix from which the daughter nuclide Re can readily be separated. This permits continuous availability of the radioisotope at the clinic and allows the preparation of Re-radiopharmaceuticals in a kit procedure as has been established for technetium radiopharmaceuticals. W/ Re generators... 

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. 

Making metastable technetium-99 is an expensive business. A cheaper, common alternative tracer is iodine-131, which emits a gamma ray when it decays. But the iodine isotope also releases beta particles that can damage tissues, making it less attractive as an imaging agent. 

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

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. 

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. 

Technetium is now moderately abundant because it accumulates in the decay products of nuclear power plants. Another isotope, technetium-99, has pharmaceutical applications, particularly for bone scans (Box 17.2). 

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... 

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