Astatine limitations

Numerous nuclear reactions have been employed to produce astatine. Three of these are particularly suited for routine preparation of the relatively long-lived isotopes with mass numbers 209, 210, and 211. The most frequently used is the ° Bi(a,xn) At (a = 1-4) reaction, in which bismuth 44, 74,120) or bismuth oxide (7,125) is bombarded by 21-to 40-MeV a-particles. The ° Bi(He, xn) At reaction can also be used to produce isotopes of astatine 152), the nuclear excitation functions (62) favor a predominant yield of ° At and °At. The routine preparation of astatine is most conveniently carried out through the ° Bi(a,xn) At nuclear reactions, from which a limited spectrum of astatine nuclides may be derived. The excitation functions for these nuclear reactions have been studied extensively (78, 89, 120). The... 

Only limited information about the electrochemical properties of astatine is available. The formation of a singly positively charged cation, At+, in aqueous and other solvent environments has been observed. A study in a nitric acid environment investigated the adsorption into ion exchange materials of this cation [206]. In a similar study in aqueous perchloric acid, the mobility of At+ was found to change with pH and the presence of a strongly water bound species, At(H20)2", with a pA of ca. 1.5 was proposed [207]. 

A serious disadvantage is that the organic compounds of thallium are formed under strong oxidative conditions and this very much limits the group of compounds which can be astatinated using this method. 

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... 

Nuclear chemistry (radiochemistry) has now become a large and very important branch of science. Over four hundred radioactive isotopes have been made in the laboratory, whereas only about three hundred stable isotopes have been detected in nature. Three elements —technetium (43), astatine (85), and promethium (61), as well as some trans-uranium elements, seem not to occur in nature, and are available only as products of artificial transmutation. The use of radioactive isotopes as tracers has become a valuable technique in scientific and medical research. The controlled release of nuclear energy promises to lead us into a new world, in which the achievement of man is no longer limited by the supply of energy available to him. 

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