Separative work isotope separation from

Formation and transport of radon ) In the present work, lead isotopes were chemically separated from the sample gas as lead sulfide since the formation of lead sulfide was inevitable under the presence of H2S in the fumarolic gas. The lead sulfide was then dissolved in a small amount of concentrated HCI and mixed with the Insta Gel(emulsion scintillator solution, Insta Gel, Packard Inc.) for the liquid scintillation counting. The chemical yield and the volume of the collected non-condensing gas were obtained from the measurement of the activities of Pb-214 and its progeny which were in radioequilibrium with their precursor Rn-222 whose concentration was determined separately by the direct method. 

From Figs. 1.1 and 1.2 it follows that the main end products of the uranium and thorium series are isotopes of lead (at the time referred to as Pb206.5 and ThO2208.4). The end products are thus isotopes of lead differing by two mass units. This observation became the motivation for the measurement of atomic weights of lead samples separated from thorium and uranium minerals. In his Nobel Lecture, Soddy describes this work as follows ... 

Since 202Hg, (1) has the highest abundance of any of the isotopes in vHg, (2) is readily available in high purity, and (3) has an life, at 2537 A., well separated from the remaining hyperfine contours, most of the experimental work in monoisotopic photosensitization has been carried out with the 202Hg isotope. 

A potentially more efficient method of enrichment would involve the use of sophisticated tunable lasers to ionize selectively and not fU. The ionized could then be made to react with negative ions to form another compound, easily separated from the mixture. For this method to work, we must construct lasers capable of producing radiation monochromatic enough to excite one isotope and not the other—a difficult challenge. 

Electro-magnetic separation is the only method by which the isotopes of an element can be completely separated from one another. The separation is carried out by the mass spectrograph which works on the principle elaborated earlier for the mass spectrometer (Chapter 13). Working of the Dempster s mass spectrograph diagramatically represented by Figure 19.4, illustrates the basics of electromagnetic separation of isotopes. 

The first product of disintegration is mesothorium I, discovered by Hahn in 1907. It is isotopic with radium and is used as a substitute for certain radium preparations. As large quantities of thorium minerals are now worked up in connection with the gas-mantle industry, and mesothorium is a by-product, it has assumed commercial importance. It is separated from thorium in monazite being precipitated along with barium as sulphate. Thorium Xy discovered by Rutherford and Soddy in 1902, is another isotope of radium. Radiothorium, RdTh, is an active isotope of thorium and cannot be separated from it directly it has to be obtained from mesothorium I by disintegration if required free from isotopes. 

If this isotope could be used for maintaining chain reactions, it would have to be separated from the bulk of uranium. This, no doubt, would be done if necessary, but it might take five to ten years before it can be done on a technical scale. Should small scale experiments show that the thorium and the bulk of uranium would not work, but the rare isotope of uranium would, we would have the task immediately to attack the question of concentrating the rare isotope of uranium. ... 

Another strand of development came from several attempts to separate some of these new radio-elements chemically, which ended in failure. First of all, in 1907 Herbert McCoy and WiUiam Ross concluded that, in the case of thorium and radiothorium, Our experiments strongly indicate that radiothorium is entirely inseparable from thorium by chemical processes, " a comment Soddy considered the first definitive statement of the chemical inseparability of what were soon to be called isotopes. Soddy himself wrote in the same year that there seemed to be no known method of separating thorium X from mesothorium.They were in fact two isotopes of thorium. Similar cases began to multiply. Bertram Boltwood discovered the radio-element ionium, which could not be chemically separated from thorium. In another famous case, Hevesy and Paneth were asked by Rutherford to try to separate radio-lead from ordinary lead and likewise failed to do so, in spite of using 20 different chemical methods. Their work was not entirely in vain, however, since it led to the development of the use of radioactive tracers, which have become an indispensable tool in modem chemistry and biochemistry. 

CPD was, of course, dependent on Chalk River for all its isotopes. Aside from the physical distance that separated them, each of these two parts of AECL had its own distinct history and culture. There were plenty of opportunities for conflict. Some scientists at Chalk River believed that their research work was for the common good and should not be appropriated for CPDs mercenary ends. Others simply resented having isotope production interfere with their access to the reactor for research. Conflicts arose over the scheduling of irradiations for CPD. Chalk River naturally wanted to plan its reactor use as thoroughly as possible. When sales were steady, CPD could give it a fair estimate of its requirements. However, when the market took an unpredicted turn, CPD was eager to change the reactor schedule immediately so that it could get its hands on the products that it needed at the earliest possible moment. 

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