Bismuth isotopes, radioactive

C. Radiochemical Syntheses and Uses of Organometallic Compounds of Radioactive Bismuth Isotopes... 

All elements heavier than bismuth are radioactive. They have no stable isotopes. Does that mean that scientists will never find another stable element in the transfermium group As they search for elements 117,119, and beyond, will they always find radioactive isotopes only ... 

Alternatives for yield determination in the absence of stable isotopic carrier are nonisotopic stable carrier and radioactive tracer, as discussed in Sections 4.5 and 6.3. Technetium, promethium, and the elements heavier than bismuth have radioactive but no stable isotopes. 

Astatine is a radioactive element that occurs in nature in uranium and thorium ores, but only to a minute extent. Samples are made by bombarding bismuth with a particles in a cyclotron, which accelerates the particles to a very high speed. Astatine isotopes do not exist long enough for its properties to be studied, but it is thought from spectroscopic measurements to have properties similar to those of iodine. 

The silver gray metal can be cut with a knife, although it only melts at 1545 °C (for comparison, iron 1538 °C). It is the rarest of the "rare earths", but is nevertheless more abundant than iodine, mercury, and silver. Thulium has few applications, especially because it is relatively expensive. The element occurs naturally as a single isotope, namely 169Tm (compare bismuth). The artificial, radioactive 170Tm is a transportable source of X-rays for testing materials. Occasionally used in laser optics and microwave technology. 

Iodine-131 was among the first radioactive isotopes used for radioimmunoconjugate preparation (Order, 1982 Regoeczi, 1984). Since the earliest studies on the efficacy of radiotherapy, additional isotopes have been employed, such as iodine-125, bismuth-212, yttrium-90, yttrium-88, technetium-99 m, copper-67, rhenium-188, rhenium-186, galium-66, galium-67, indium-111, indium-114 m, indium-115, and boron-10. 

Figure 10.2 The radioactive stability of the elements. The x axis is proton number (up to Z = 83, bismuth), the y axis the neutron number (N). Stable isotopes are shown in black and radioactive isotopes in grey, indicating the relative excess of radioactive isotopes over stable isotopes in nature, and the fact that as proton number increases, the neutron number has to increase faster to maintain stability. The basic data for this figure are given in Appendix VI.

Table A. 1 comprises the stable elements from hydrogen to bismuth with the radioactive elements technetium and promethium omitted. Natural variations in isotopic composition of some elements such as carbon or lead do not allow for more accurate values, a fact also reflected in the accuracy of their relative atomic mass. However, exact masses of the isotopes are not affected by varying abundances. The isotopic masses listed may differ up to some 10 u in other publications.

ISOTOPES There are a total of 59 radioactive isotopes for bismuth, ranging in half-lives from a few milliseconds to thousands of years. At one time it was thought that there was just one stable isotope (Bi-209), but it was later found that Bi-209 is radioactive with a half-life of 19,000,000,000,000,000,000 years. Such a long half-life means that BI-209 has not completely disintegrated and Is still found In nature, and Is thus considered stable. In this case, BI-209 makes up 100% of Bismuth s natural abundance. 

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. 

If you look at the periodic table, you will notice that all elements after bismuth, atomic number 83, have their atomic weight denoted by an integer within parentheses. Such large nuclei are unstable and undergo radioactivity, the spontaneous disintegration by the emission of particles. The atomic weight shown on the periodic table is the mass number of the most common isotope of each radioactive element. 

Astatine (from the Greek astatos unstable) is highly unstable and radioactive. It was synthesized in 1940 by D. R. Corson, K. R. MacKenzie, and E. Segre at the University of California by bombarding bismuth with a-particles. The resulting 209-2iiy isotopes are relatively long-lived... 

Sir Alexander Fleck, 1889—. Author of many research papers on the radioactive isotopes. He proved the inseparability of uranium Xi and radioaetinium from thorium, of thorium B and actinium B from lead, of mesothorium 2 from actinium, of radium E from bismuth, and of radium A from polonium, and confirmed the discovery of uranium X3 by Faj ans and O. H. Gohring. Chairman of Imperial Chemical Industries, Ltd. See also ref. (1S7). 

Thus it is evident that there are three natural radioactive isotopes of thallium, seven of lead, four of bismuth, seven elements in the polonium pleiad, three inert radioactive gases, four isotopes of radium, two of actinium, six of thorium, three eka-tantalums, and three uraniums. 

The oldest, most well-established chemical separation technique is precipitation. Because the amount of the radionuclide present may be very small, carriers are frequently used. The carrier is added in macroscopic quantities and ensures the radioactive species will be part of a kinetic and thermodynamic equilibrium system. Recovery of the carrier also serves as a measure of the yield of the separation. It is important that there is an isotopic exchange between the carrier and the radionuclide. There is the related phenomenon of co-precipitation wherein the radionuclide is incorporated into or adsorbed on the surface of a precipitate that does not involve an isotope of the radionuclide or isomorphously replaces one of the elements in the precipitate. Examples of this behavior are the sorption of radionuclides by Fe(OH)3 or the co-precipitation of the actinides with LaF3. Separation by precipitation is largely restricted to laboratory procedures and apart from the bismuth phosphate process used in World War II to purify Pu, has little commercial application. 

All isotopes heavier than bismuth-209 are radioactive, even though they may occur naturally. 

All isotopes of all elements beyond bismuth (Z 83) are radioactive. In particular, isotope 227 of actinium (Z = 89) decays mainly with the emission of particles, forming a0Th227 (Chap. 27). It has been shown, however, that about 1 percent of this actinium isotope decays in a differ-... 

All elements beyond bismuth in the Periodic Table are radioactive, most of these having several isotopes (or nuclides), each with a characteristic half-life. A small number of elements of low atomic number (K, Rb, Sm, Lu, Re, and perhaps La and H) each have one naturally occurring radioisotope also. In addition, over 700 radioisotopes have been made artificially (p. 466). 

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