Production methods heavy elements

The applicability of heavy-ion reactions to the production of heavy elements increased with the development of efficient heavy-ion accelerators at Berkeley, Dubna and Darmstadt. On the other hand, the importance of instrumental methods... 

To give one a feel for the magnitude of the quantities involved, we outline below a very simple schematic method for estimating heavy-element production cross sections. It is intended to show the relevant factors and should not be taken too seriously, except to indicate the order of magnitude of a particular formation cross section. 

There was also great uncertainty of the production yields for SHEs. Closely related to the fission probability of SHEs in the ground-state, the survival of the compound nuclei formed after complete fusion was difficult to predict. Even the best choice of the reaction mechanism, fusion or transfer of nucleons, was critically debated. However, as soon as experiments could be performed without technical limitations, it turned out that the most successful methods for the laboratory synthesis of heavy elements are fusion-evaporation reactions using heavy-element targets, recoil-separation techniques, and the identification of the nuclei by generic ties to known daughter decays after implantation into position-sensitive detectors [13-15],... 

II. Emergence-Angle Experiments.— Two methods were used in the present work, both based on the fact that such indirect rays as may exist are produced at a variety of depths averaging somewhat greater than the mean depth of production of rays in the continuous spectrum. This is obvious qualitatively from the fact that, in any fairly heavy element, X-rays of the types needed for fluorescence of its K series are more penetrating than the cathode rays producing them. 

Photoreactions in which two or more particles are emitted, hke those produced by heavy particles should be the products of the decay of compound nuclei and their relative cross sections should be calculable by statistical methods. Moreover, the relative yields of the (y, 2n) to the (y, n) reactions should throw light on the extent to which the (y, n) reaction is produced by direct interaction. For such studies, however, it is best to take a heavy element for which the (y, p) or (y, a) reactions are known to be infrequent. Wilkinson and his collaborators... 

HIBA/sodium octanesuIfonate-a-HIBA systems were employed for separation and assay of lanthanide fission products. In one of the studies, the HPLC method was used to separate and estimate a lanthanide fission product, e.g., lanthanum and a heavy element, e.g., uranium. The bum-up obtained was found to be in good agreement with the conventional mass spectrometric method. In another study. 

The application of nuclear forensic techniques to samples of purified heavy elements is well developed however, when applied to unseparated spent reactor fuel, the methods become more complicated. The radionuclide content of a spent fuel sample is not controlled solely by radioactive decay, but is strongly influenced by neutron-induced transmutation. Chronometry based on the decay of the light plutonium isotopes cannot be performed due to the initial presence of an overwhelming quantity of uranium. The isotopic distribution of the plutonium isotopes and the concentration of fission products can provide a means by which the degree of transmutation can be estimated, unless the material started out as MOX fuel (where reprocessed plutonium is incorporated into fuel fabricated from uranium with insufficient fissile content to support the reactor application). More study is needed to extend the methodology to unprocessed fuel. 

This chapter describes tire problem of cost visibility we addressed in Chapters 24 and 25. Plumbco faces a situation we find increasingly common. Its operations include heavy elements of both manufacturing and distribution, but its methods for determining product and customer profitability were outdated. The case study shows how company management can expeditiously get a handle on profitability for decision making. 

The radiochemist may have need to recover rare gases from a variety of target materials, though most usually from heavy elements in which fission has occurred. Any method suitable for bringing the target material into a clear solution may be used in principle. Since the recovery of the rare gases inust be effected from the volatile products of solution, solution procedures which produce the more tractable gdseous products are to be desired. Methods reported in the literature for the solution of spent fuel elements and re-... 

Recent applications of photon activation to the analysis of heavy elements include the determination of Te, Sr, and Pb. Campbell and Steele measured Te in the presence of U by Ge(Li) spectrometry of the activated Te isotope [ Te(y,n) Te] with a half-life of 17 d. The method is useful because it avoids the complications arising in n.a.a. caused by fission of the uranium giving rise to direct and spectral interferences from fission products. The measurement of "Sr induced by Sr(), n) and Sr(y,y ) reactions using 30 MeV Bremsstrahlung has been applied to the analysis of Sr in sea-water at the 8 p.p.m. level this involved a radiochemical separation of the 2—8 h Sr. The (y,n) reaction of Pb has been used for the determination of Pb in milk powder.Measurement of the Pb isotope (/ 52 h) after a non-specific sulphate precipitation of the Pb is sufficient to attain a limit of detection of 0.5 //g. The activity was measured with a NaI(TI) detector after "Sr, which was also produced, had decayed. 

Dissolved Minerals. The most significant source of minerals for sustainable recovery may be ocean waters which contain nearly all the known elements in some degree of solution. Production of dissolved minerals from seawater is limited to fresh water, magnesium, magnesium compounds (qv), salt, bromine, and heavy water, ie, deuterium oxide. Considerable development of techniques for recovery of copper, gold, and uranium by solution or bacterial methods has been carried out in several countries for appHcation onshore. These methods are expected to be fully transferable to the marine environment (5). The potential for extraction of dissolved materials from naturally enriched sources, such as hydrothermal vents, may be high. 

The heavy metal salts, ia contrast to the alkah metal salts, have lower melting points and are more soluble ia organic solvents, eg, methylene chloride, chloroform, tetrahydrofiiran, and benzene. They are slightly soluble ia water, alcohol, ahphatic hydrocarbons, and ethyl ether (18). Their thermal decompositions have been extensively studied by dta and tga (thermal gravimetric analysis) methods. They decompose to the metal sulfides and gaseous products, which are primarily carbonyl sulfide and carbon disulfide ia varying ratios. In some cases, the dialkyl xanthate forms. Solvent extraction studies of a large number of elements as their xanthate salts have been reported (19). 

Often the products of nuclear reactions have very short half-lives. This is especially true for the heaviest elements obtained by bombardment of heavy targets with heavy ions. To identify and characterize such short-lived nuclides, fast separations are required solvent extraction techniques are well suited to provide the required fast separations. For example, the SISAK method [68] has been successfully used in conjunction with in-line gas jet separators at heavy ion accelerators to identify short half-life actinide isotopes produced by collision of heavy atoms. The Sisak method involves use of centrifugal contactors, with phase residence times as low as tenths of a second, in conjunction with in-line radiometric detection equipment. 

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