Astatine-211, half-life

The element exists as an intermediate in uranium and thorium minerals through their decay. There is no stable isotope. The longest-living isotope has a half-life of 8.3 hours. In the crust of the Earth, the total steady-state mass is estimated at a few tens of grams. Thus astatine is the rarest element (record ). A few atoms of this relative of iodine can be found in all uranium ore. It exhibits certain metallic properties. 

Astatine - the atomic number is 85 and the chemical symbol is At. The name derives from the Greek astatos for unstable since it is an unstable element. It was first thought to have been discovered in nature in 1931 and was named alabamine. When it was determined that there are no stable nuclides of this element in nature, that claim was discarded. It was later shown that astatine had been synthesized by the physicists Dale R. Corson, K. R. Mackenzie and Emilio Segre at the University of California lab in Berkeley, California in 1940 who bombarded bismuth with alpha particles, in the reaction Bi ( He, 2n ) "At. Independently, a claim about finding some x-ray lines of astatine was the basis for claiming discovery of an element helvetium, which was made in Bern, Switzerland. However, the very short half-life precluded any chemical separation and identification. The longest half-life associated with this unstable element is 8.1 hour °At. 

ISOTOPES All 41 isotopes of astatine are radioactive, with half-lives ranging from 125 nanoseconds to 8.1 hours. The isotope As-210, the most stable isotope with an 8.1-hour half-life, is used to determine the atomic weight of astatine. As-210 decays by alpha decay into bismuth-206 or by electron capture into polonium-210. 

Astatine does not have stable or useful compounds. Like a halogen, it will form halogen salts with a few other elements. No significant astatine commercial compounds have been produced with the exception of astatine-211, which has a half-life of just over seven hours and is used as a radioactive tracer for thyroid diseases. 

Astatine is highly radioactive and only produced and isolated in very small quantities isotope with the longest half-life (8.3 h) considered. 

In 1940 D. R. Corson, K. R. Mackenzie, and E. Segre at the University of California bombarded bismuth with alpha particles (26, 27). Preliminary tracer studies indicated that they had obtained element 85, which appeared to possess metallic properties. The pressure of war work prevented a continuation of these studies at the time. After the war, the investigators resumed their work, and in 1947 proposed the name astatine, symbol At, for their element. The name comes from the Greek word for unstable, since this element is the only halogen without stable isotopes (28). The longest lived isotope is At210 with a half-life of 8.3 hours and a very high activity. 

Astatine-211, half-life, 216 Au-191, sorbent/complex combination, 9 Au-195, activity, 44 Au-195m... 

J Since the most stable isotope of astatine has a half-life or only 8.3 hours, Ihc chemistry of this halogen has not been studied extensively. In Ihc following discussion generalities made eboul ihc hnlogens may or may not include astatine. In ihe present instance AlBr and AtCI have been prepared. Sec the discussion of nsiaimc chemistry later in this chapter. 

The heaviest member of Group 17, astatine (At), has only very short-lived isotopes. 219At is a daughter of 223Fr and a granddaughter of 227Ac. 219At has a half-life much shorter than either Ac or Fr and its oceanic concentration profiles... 

Although there are a number of isotopes of francium, most decay very rapidly to other elements. Most isotopes with masses of 223 AMU and lower emit tt-particles (consisting of two protons and two neutrons) to become astatine. Some low mass francium isotopes can also undergo electron capture (the conversion of a proton to a neutron through the absorption of an electron) to become radon. Francium isotopes with masses of 220 AMU and higher can undergo /3-decay (the conversion of a neutron to a proton through the emission of an electron) to become radium. Francium-223 is the most stable isotope and has a half-life of 21.8 minutes. 

Astatine-211 (half-life 7.214 h), produced in the 209Bi (a, 2n) nuclear reaction504, under-... 

Astatination by means of nucleophilic halogen exchange, occasionally with the help of catalysts, and electrophilic replacement via demetalation seem to have become the preferred techniques. Short synthesis and separation time together with the possibility of carrier-free preparation of labelled compounds are especially important factors, bearing in mind the short half-life of astatine isotopes and the requirement of high specific activity for chemical and biomedical investigations. 

The chemistry of astatine is reviewed in Standard Potentials and elsewhere (148). Because of the short half-life of this element ( 8 hr) not much is known of its chemistry. There are no reports of its free radicals in aqueous solution. 

Although astatine is a member of Group 7A, its chemistry is of no practical importance because all its known isotopes are radioactive. The longest-lived isotope, 210At, has a half-life of only 8.3 hours. 

Astatine-211 is a promising radionuclide for systemic therapy1 3 due to its decay properties with a half-life of 7.2 hours and an effective emission of one a-particle per decay. However, the weakness of the astatine-protein bond formed after direct astatination1 4 has so far limited its clinical use. To overcome these problems indirect labelling methods have been tried such as the use of ALsuccinimidyl-(trialkylstannyl) benzoate as an intermediate for the astatination of antibodies using conjugation procedures.5 8... 

The isotopes with the longest half life are astatine-209, astatine-210, and astatine-211. The numbers after the names here are the atomic weights of the isotopes. These isotopes have half lives of 5.4 to 8.1 hours. The half life of a radioactive isotope is the time it takes for half of a sample of the element to break down. In 5.4 hours, only half of a sample of astatine-209 will still be astatine-209. Another 5.4 hours later, only 25 percent of it will remain. 

Because of the very low half-life of its isotopes, the radioactive astatine has no significance for living systems. 

Astatine is a radioactive element that occurs in uranium ores, but only to a tiny extent. Its most stable isotope, °At, has a half-life of 8.3 h. The isotopes formed in uranium ores have much shorter lifetimes. The properties of astatine are surmised from spectroscopic measurements. Astatine is created by bombarding bismuth with alpha particles in a cyclotron, which accelerates particles to high speed. 

The most difficult problem in the radiochemistry of TAE is possible formation of a compound which has no analogs in chemistry of the known elements. The only example of a satisfactory solution to a similar problem in modem radiochemistry was the assignment of a cationic form of astatine [123]. It had required many years of experimentation despite the fact that the utilized At isotope had convenient half-life and was readily available in high enough activity to allow thorough experimentation. 

The element astatine also belongs to the Group 7A family. However, all isotopes of astatine are radioactive its longest-hved isotope is astatine-210, which has a half-life of 8.3 hours. Therefore it is both difflcult and expensive to study astatine in the laboratory. 

The most stable isotope of astatine is °At, which has a half-life of 8.1 hours. Other isotopes have mass numbers ranging from 193 to 223 and half-lives ranging from 125 nanoseconds ( At) to 7.2 hours ( At). Astatine is known to form interhalogen compounds with bromine (AtBr), chlorine (AtCl), and iodine (Atl). Additional compounds (HAt and CHjAt) have also been detected. 

Because of its scarcity and short half-life, there were no commercial uses for astatine as of 2003. Researchers are investigating astatine as a means of... 

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