Synthesis of Superheavy Elements
The Island of Stability of spherical superheavy nuclides exists at the extreme limit of the Chart of the Nuclides, beyond regions of nuclear stability associated with deformed nuclear shapes. In this chapter, the reactions that are used to synthesize thes
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Abstract The Island of Stability of spherical superheavy nuclides exists at the extreme limit of the Chart of the Nuclides, beyond regions of nuclear stability associated with deformed nuclear shapes. In this chapter, the reactions that are used to synthesize these transactinide nuclides are discussed. Particular emphasis is placed on the production of nuclides with decay properties that are conducive to a radiochemical measurement. The cold- and hot-fusion reactions that lead to the formation of evaporation residues are discussed, as are the physical techniques that have been used in production experiments. Recent results from 48Ca-induced fusion reactions are included. Speculative methods of producing the more neutronrich nuclides that populate the approaches to the center of the Island of Stability are also presented.
1 Introduction The known elements were organized into the Periodic Table in the nineteenth century, first by atomic weight and then by atomic number. In both versions, uranium was the most extreme element. Since that time, the possibility of extension of the Periodic Table to unknown atomic numbers has captured the imaginations of many people, among them scientists and students of chemistry and physics. Can they be produced? If so, what are their chemical and physical properties? Does the Periodic Table have an extreme limit? These questions are some of the most fundamental in the chemical sciences. The discovery of the neutron and the development of the particle accelerator provided the means for exploration of the Periodic Table beyond uranium. In 1934,
K. J. Moody (&) Lawrence Livermore National Laboratory, Livermore, CA, USA e-mail: [email protected]
M. Schädel and D. Shaughnessy (eds.), The Chemistry of Superheavy Elements, DOI: 10.1007/978-3-642-37466-1_1, Springer-Verlag Berlin Heidelberg 2014
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K. J. Moody
Fermi irradiated uranium with slow neutrons, and observed a variety of radioactivities that he tentatively identified as being transuranium elements [1]. We now know that these radioactive species were the products of the fission of the 235U in the sample. Study of the chemical properties of these new nuclides led to the subsequent discovery of fission in 1939 [2, 3]. Explanation of the fission process was closely connected to the creation of the liquid-drop model [4–6], in which the nucleus is treated like an incompressible charged fluid with surface tension. See ‘‘Nuclear Structure of Superheavy Elements’’ for more information on nuclear structure and the stability of the heaviest nuclides. The liquid-drop model was very successful in reproducing the beta-stable nuclei at a given atomic mass (A) as a function of atomic number (Z) and neutron number (N), and the global behavior of nuclear masses and binding energies. Early versions of the liquid-drop model predicted that the nucleus would lose its stability to even small changes in nuclear shape when Z2/A [ 39, around element 100 for beta-stable nuclei [6, 7]. At this point, the electrostatic repulsion between the protons in th
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