Half-life of cobalt

An instrument for cancer treatment containing a cobalt-60 source was manufactured in 1978. In 1995 it was removed from service and, in error, was buried in a landfill with the source still in place. What percentage of its inihal radioactivity will remain in the year 2010 (See Table 10.2 for the half-life of cobalt-60.)... 

Cobalt-60 undergoes radioactive decay with the emi.sskm of beta particles and strong gamma radiation. It ultimately decays to nonradioactive nickel. The half-life of cobalt-60 is 5.27 years. This is short enough to make isolation a useful treatment strategy for contaminated areas. In some cases, simply waiting 10 to 20 years allows for sufficient decay to make the site acceptable for use again. 

The half-life of cobalt-60 is 5.3 yr. How much of a 1.000-mg sample of cobalt-60 is left after 15.9 yr ... 

As a radioactive sample decays, the amount of radiation emanating from the sample decays as well. For example, the half-life of cobalt-60 is 5.26 yr. The 4.0-mCi sample of cobalt-60 would, after 5.26 yr, have a radiation activity of 2.0 mCi, or 7.5 x 10 Bq. 

A 1.40-g sample containing radioactive cobalt was kept for 2.50 a, at which time it was found to contain 0.266 g of 67Co. The half-life of 67Co is 5.27 a. What percentage (by mass) of the original sample was f,Co ... 

The radioisotope cobalt-60, with a half-life of 5.27 years (1925.3 days) through beta ((3) emission, decays to form the stable element nickel-60. It is used to test welds and metal casts for flaws, to irradiate food crops to prolong freshness, as a portable source of ionizing gamma (Y) radiation, for radiation research, and for a medical source of radiation to treat cancers and other diseases. 

It was soon noticed, to the great satisfaction of theoreticians, that the brightness of the object was falling at the rate implied by the decay of cobalt-56 (with a mean lifetime of 111 days or a half-life of 77 days), precisely as predicted. This decay was considered to be responsible for the snpernova s light emissions at that stage. It was then replaced by the decay of cobalt-57, which in good time probably handed over to titaninm-44. 

Sediments in the Mississippi River were accidentally contaminated with a low-level radioactive waste material that leaked from a nuclear power plant on the river. Pore water concentrations of radioactive compounds were measured following the spill and found to be 10 g/m over a 2-mm depth. The water contamination was 30% radioactive cesium ( Cs), with a half-life of 30 years, and 70% radioactive cobalt ( °Co), with a half-life of 6 years. Objections by the local residents are preventing clean-up efforts because some professor at the local state university convinced them that dredging the sediments and placing them in a disposal facility downstream would expose the residents to still more radioactivity. The state has decided that the sediments should be capped with 10 cm of clay and needs a quick estimate of the diffusion of radioactive material through the clay cap (Figure E2.8.1). If the drinking water limit (10 g/m ) is reached at mid-depth in the cap, the state will increase its thickness. Will this occur ... 

The damaging effects that radioactivity can have on tissues are not all bad. To treat cancers, we want to kill cells - albeit the unhealthy, frantically replicating tumour cells, not healthy cells. If radioisotopes can be localized in tumours, they do their destructive business to good effect. Cobalt-60, made by neutron bombardment of stable cobalt-59, is a radioisotope with a half-life of 5.3 years that is used to treat cancer. 

The most widely used radioactive isotopes in medical and industrial applications are cobalt 60 ( C), cesium 137 ( Cs), and iridium 192 ( lr). The half-life of is 5.3 years, that of Cs is 30 years, and the half-life of Ir is 74 days. When used for irradiation the isotope is generally in the form of a pellet size, 1.5 x 1.5 mm, loaded into a stainless steel capsule and sealed. Unlike electron beam or x-rays, gamma rays cannot be turned off. 

Cobalt must be supplied in the diet in its physiologically active form, vitamin B12. GI absorption of cobalt is about 25%, with wide individual variation excretion occurs mainly via the urine. The major part is excreted within days and the rest has a biological half-life of about two years. Originally, the therapy for pernicious anemia was to have patients eat large amounts of liver. The most reliable treatment now is monthly injections of cobalamin. 

The treatment of diorganozincs or organozinc halides with cobalt bromide in THF NMP mixtures provides blue solutions of organocobalt reagents, which have a half-life of several hours at -20 °C.25,26 Carbonylation reactions with these new cobalt reagents proceed well simply by bubbling carbon monoxide... 

Isotope dilution is applicable to any element for which an enriched isotope is available. Figure 1.1 of Chapter 1 indicates which elements are amenable to isotope dilution in most cases the natural element has at least two stable isotopes, but this is not necessarily the case. For example, 232Th, though radioactive (half-life of 1.4 X 1010 years), is present in the earth s crust 230Th (half-life of 7.5 X 104 years), an isotope present in nature at such low levels as to be negligible for most applications, is used as a spike for isotope dilution purposes in the author s laboratory. Another common example is the use of 233U (a synthetic isotope) as a spike for uranium analyses. The only elements not amenable to the technique are those, like cobalt and arsenic, that have only one stable isotope and all of whose radioactive isotopes have half-lives so short as to preclude their use. 

The medical applications of nuclear technology range from in vitro and in vivo injections for diagnostic tests to cobalt radiation for cancer therapy. A new medical specialty was created, a family of compact cyclotrons was developed to provide short-lived nuclides, and a sizable industry evolved to produce technetium. Until the nuclear industry was created, technetium had been missing from the chart of chemical elements because the half-life of the most stable member was too short, 21,000 years. Technetium and several other nuclides of importance here are discussed elsewhere in the chapter in connection with their production (see Table 21.19).60,61... 

Transferrin is mainly synthesized in the hepatocytes. There are about 20 known variants. Iron is transported by transferrin (approx. 30% of transferrin is saturated with iron). With the help of a membrane receptor, the iron-transferrin complex is taken up and released in the liver cell, where it is immediately bound (because of its toxicity) to ferritin. The liver cells take up iron predominantly from transferrin, to a lesser degree also from haptoglobin, haemopexin, lactoferrin and circulating ferrin. Transferrin, which is mainly formed in the hepatocytes, may also bind and transport, in decreasing order, chromium, copper, manganese, cobalt, cadmium, zinc and nickel. The half-life of transferrin is 1 - 2 hours, which is very short in view of its total blood concentration of 3-4 mg. Approximately 0.4 g ferritin iron is stored in the liver. In the case of transferrin deficiency, its bacteriostatic and fungistatic effects are also reduced. Transferrin without iron saturation is known as apo-transferrin. (31, 66, 67)... 

Cobalt-60, with a half-life of 5 years, is used in cancer radiation treatments. If a hospital purchases a supply of 30.0 g, how much would be left after 15 years ... 

Cyanombalamln Radioactive Cobalt ( Co) Capsules, USP. Cyanocobalamin Co capsules contain cyanocobaJ-amin in which some of the molecules contain radioactive cobalt ( Co), Each microgram of this cyanocobalamin preparation has a specific activity of not less than 0.02 MBq (0.. i Ci). The USP cautions that in making dosage calculations one. should correct for radioactive decay. The radioactive half-life of Co is 270 days. 

Cobalt-60 and iodine-131 are used in treatments for some types of cancer. Cobalt-60 decays with a half-life of 5.27 years, emitting beta particles with a maximum energy of 0.32 MeV. Iodine-131 decays with a half-life of 8.04 days, emitting beta particles with a maximum energy of 0.60 MeV. 

A sealed radioactive source used for physics demonstrations in 1940 contained 10 microcuries (/xCi) of 60Co (cobalt-60). Given a half-life of 1900 days for 60Co, what would be the source strength in 1993 ... 

The cobalt treatments used in medicine to arrest certain types of cancer rely on the ability of gamma rays to destroy cancerous tissues. Cobalt-60 decays with the emission of beta particles and gamma rays, with a half-life of 5.27 years. 

This pathway cannot continue indefinitely, however. What limits the process is the relationship between neutron capture time and the half-life of isotopes produced by neutron capture. The reactions just described, for example, which successively change iron to cobalt and nickel, take place very slowly and are, therefore, known as slow neutron capture reactions or, more simply, as s reactions. They are called "slow" because, on average, hundreds to thousands of years may pass before any given nucleus absorbs a neutron. These reactions can occur because they all involve the presence of a stable isotope at some point, for instance, iron-57, iron-58, or cobalt-59. As long as these isotopes are present—or as long as isotopes with half-lives greater than a few hundreds or thousands of years are present—there is enough time for neutron capture to occur. 

Cobalt-60, which is used in radiation therapy, has a half-life of 5.26 years. 

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