Heavy-ion accelerators

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. 

The fundamental usefulness of exotic nuclei and their decay assures a continuing interest in the field. New heavy-ion accelerators will ensure that... 

All the elements beyond Z = 94 are synthetic and are produced by the bombardment of target nuclei with a smaller projectile. For example, German scientists have made two atoms of element 112, ununbiium (Uub), by bombarding lead-208 atoms with zinc-70 atoms in a heavy-ion accelerator ... 

Reactions of atomic carbon, produced by nuclear reactions, with a number of hydrocarbons have been studied by Wolfgang and his collaborators (69). To minimize radiation induced secondary reactions which occur when use is made of C14, a technique has been developed using short-lived C11 produced by a neutron exchange reaction between a platinum foil and a C12 ion beam from a heavy ion accelerator. Part of the scattered Cu atoms has been allowed to penetrate through the thin brass foil wall of a brass vessel and come in contact with the compound wrhose reaction is studied. Products have been analyzed by gas chromatography using a technique of simultaneous mass and radioactivity determination. 

G. J. Mathews, R. C. Haight, and R. W. Bauer, "Proceedings of the Workshop on the Prospects for Research with Radioactive Beams from Heavy-Ion Accelerators", J. M. Nitschke (ed.) (Washington, DC 1984). 

In principal at least, a heavy-ion accelerator with the capabilities of TASCC should be ideally suited both to the specific synthesis of a selected group of isotopes and to high current production runs of a wide range of isotopes. 

Chalk River is not the only laboratory with an isotope separator on-line to a heavy-ion accelerator, Berkeley, Oak Ridge and GSI Darmstadt have already proven the value of such a combination in studying exotic nuclei. We believe that the versatility and energy range of TASCC, together with the proven quality of separated beams from the ISOL, will make the Chalk River facility among the best in the field. 

Recently, the SISAK technique has been applied for the separation of new, neutron-rich neptunium isotopes formed in direct transfer reactions between 8Xe projectiles and targets of Pu at the UNI LAC heavy-ion accelerator. The SISAK system consisted of three mixer-centrifuge units and a degasser. 

The study of the chemical properties of the heaviest known elements in the Periodic Table is an extremely challenging task and requires the development of unique experimental methods, but also the persistence to continuously improve all the techniques and components involved. The difficulties are numerous. First, elements at the upper end of the Periodic Table can only be artificially synthesized "one-atom-at-a-time" at heavy ion accelerators, requiring highest possible sensitivity. Second, due to the relatively short half-lives of all known transactinide nuclides, very rapid and at the same time selective and efficient separation procedures have to be developed. Finally, sophisticated detection systems are needed which allow the efficient detection of the nuclear decay of the separated species and therefore offer unequivocal proof that the observed decay signature originated indeed form a single atom of a transactinide element. 

Fig. 3. Allegorical view of heavy-ion accelerator projects launched in the early seventieths for a journey to the island of superheavy elements. The flags indicate characteristic projectile beams offered by the facilities, see text. Cartoon provided by G.N. Flerov [13].

The various types of accelerators offer the possibility of applying a great variety of projectiles of different energies. The most frequently used projectiles are protons, deuterons and a particles. Some features of the reactions induced by these partieles are summarized in Table 12.4. Neutrons may be produced indirectly by nuclear reactions, y rays are generated as bremsstrahlung in electron accelerators, and heavy ions are available in heavy-ion accelerators. 

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... 

Heavy ions such as Li, °B or others may also be used for charged particle activation, provided that a suitable heavy-ion accelerator is available. Examples of activation analysis by charged particles are given in Table 17.4. 

The expectation that superheavy elements will be detected by chemical and other identification procedures, even with these very small-cross sections, is now shifting to the heavy-ion accelerator laboratory (GSI) in Germany. There is the hope that the use of other heavy ions (including ions up to uranium) and greater beam intensities will lead to the synthesis and identification of superheavy elements. There are also several groups associated with GSI presently developing setups to detect superheavy elements using chemical separation methods similar to those described above as well as phase separations. 

Beam Exposure and Research Facility) chamber of the ISL heavy ion accelerator of the Hahn-Meitner-Institute, Berlin, Germany, at a flux of typically 0.1 nA up to fluences of 5><10 cm. The resulting latent SHI tracks produced in the oxide layer were etched by 1.35 wt.% HF solution at 20 1 C for 40 min, until the track opening was detected. The geometry of etched tracks (nanopores) is a truncated cone with the base diameter of 150-200 nm at the Si/SiOa interface and 250-300 nm on the top. The final depth of pores (200 nm) was less than the initial thickness of Si02 layer due to etching process of Si02 film. 

Giving a rigorous account of relativistic effects is now an important goal in theoretical and experimental studies because of recent progress made in experimental techniques and because of the accuracy currently achievable in measurements, e.g. in atomic and molecular spectroscopy, or in view of newly available laser techniques. Present accessible energies in heavy-ion accelerators allow a new generation of experiments with ultrarelativistic ions, which, for example, enable us to probe the structure of the vacuum via the electromagnetic particle-antiparticle pair creation. 

Chemical studies of these elements must be performed with isotopes having not only a fleeting existence but producible only in atom quantities. In Table 1 we list the most frequently made isotopes, their half lives, and the atoms that have been synthesized for each data point. Except for 255] the nuclides listed can be created only by nuclear reactions between accelerated charged particles and transplutonium target nuclei. For this reason and the short lifetimes of the isotopes, all chemical studies are carried out at large heavy-ion accelerators. Such research calls upon nuclear physics for the methods of element synthesis and detection while the research goals are aimed toward atomic and chemical properties. Therefore, this field of research most easily falls into the domain of the nuclear chemist. 

The heavier elements (transactinides), Z=104 (1969) through 106 (1974) were produced in heavy-ion accelerators by bombardment of heavy actinide (plutonium-californium) targets with light ions (carbon, boron, neon, oxygen), so called hot-fiision reactions. The institutions involved in the production of these elements were the LBNL (USA) and the JINR (Russia) (see Ref. 31 for a review). 

Particle-producing machines currently used Nuclear reactor Cyclotron Cyclotron (for deu-terons) Cyclotron or proton synchrotron Electron synchrotron or linear Heavy ion accelerator Proton synchrotron ... 

Ion-track technology based on the irradiation of thin films of various materials with accelerated heavy ions is one example of industrial application of ionizing radiation (Waheed et al. 2009). Modern heavy ion accelerators employed for irradiation of materials on the industrial scale provide beams in the 10-100 MeV/u energy range, which expands the treatment depth of considered films up to millimeters (Apel 2003). 

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