Superheavy transactinide elements

Relativistic quantum chemistry of superheavy transactinide elements 243... 

Main, G.L., Styszynski, J. Ab initio all-electron fully relativistic Dirac-Fock-Breit calculations for molecules of the superheavy transactinide elements rutherfordium tetrachloride. J. Chem. Phys. 109, 4448-4455 (1998)... 

One of the most important and most fascinating questions for a chemist is the one about the position of the superheavy elements in the Periodic Table of the Elements how well accommodates the Periodic Table these elements as transition metals in the seventh period. Do the rules of the Periodic Table still hold for the heaviest elements What is a valid architecture of the Periodic Table at its upper end The main body of information to answer this question from our today s knowledge of the chemistry of superheavy or transactinide elements is embraced between the two mainly "nuclear" oriented chapters at the beginning and at the end. 

Transactinide elements, sometimes also called superheavy elements, belong to the 7th period of the periodic table, and only a handful of transactinide compounds have been prepared so far. There are a number of interesting aspects in superheavy chemistry [16] (see also chapter 1 of this book), but our interest is mostly theoretical in nature. Transactinide compounds can easily be treated with RECPs with the f electrons effectively removed from the valence space. Hence the RECP approach for transactinide compounds is less expensive compared to compounds containing actinide elements. However, spin-orbit interactions are important, and in sections 4 and 5 of this chapter we will discuss such... 

Superheavy elements are those with Z > 104 (transactinides). One may distinguish the d elements (Z=104-112) and the superheavy Ip elements (Z=113-118). Considerable progress has been made in the production of such elements. Element 104-106 have isotopes which are stable enough to perform chemical experiments [141, 142], while for elements such as element 114, both the production rate and the lifetimes are too small to allow for experimental chemical investigations. Besides experiments, relativistic density functional calculations have been performed for compounds of the 6d elements. A detailed account can be found in chapter 1 of this volume. 

Superheavy elements are defined as the transactinide elements—elements with an atomic number greater than 103. The current production of new superheavy elements takes place mostly at four locations around the world the Lawrence Berkeley National Laboratory (LBNL) at Berkeley, California the GSI Helmholtz Centre for Heavy Ion Research (GSI) at Darmstadt, Germany the Joint Institute for Nuclear Research (JINR) at Dubna, Russia and the Superheavy Element Laboratory of the Institute of Physical and Chemical Research (RIKEN) at Nishina, Japan. As of 2012, the discoveries of elements 113-118 have all been reported. The discoveries of four of these elements, however, are still awaiting independent confirmation from the other laboratories. 

The microscopic stabilization of a Z = 114 nucleus results in a spherical nucleus that is more strongly bound than predicted by the macroscopic model. This effect produces a barrier to deformations leading to fission where there would otherwise be none [10, 12, 13, 23, 25-27]. At the time of these model calculations, the Periodic Table ended at the extreme limit of the actinides (Z = 103), with some experimental evidence for observation of the first transactinide elements. The overall trend with increasing atomic number was shorter half-lives and decreasing resistance to decay by spontaneous fission. The shell-model calculations indicated that well beyond the limits of the known elements the trends might reverse, allowing an extension of the Periodic Table [9]. This led to the concept of an Island of Stability . The term superheavy elements was coined to describe the nuclides occupying the Island. 

The nuclear models that resulted in the prediction of an island of superheavy nuclei have evolved in response to experimental measurements of the decay properties of the heaviest elements. While the prediction of a spherical magic N = 184 is robust and persists across the models [8], the shell closure associated with Z — 114 is weaker, and different models place it at higher atomic numbers, from Z = 120 to 126 [60-69] or even higher [70] (see Nuclear Structure of Superheavy Elements ). Interpretation of the decay properties of the heaviest elements may support this [71, 72], but the most part decay and reaction data do not conclusively establish the location of the closed proton shell. Because of this, the domain of the superheavy elements can be considered to start at approximately Z = 106 (seaborgium), the point at which the liquid-drop fission barrier has vanished [9]. For our purposes, the transactinide elements (Z > 103) will be considered to be superheavy (see Nuclear Structure of Superheavy Elements ). 

Though the " Ca-produced transactinide elements can be relatively resistant to spontaneous fission decay, the local increase in a-decay Q value with an increase in atomic number results in an overall decrease in half-life [329]. The decays of the " Ca-produced superheavy nuclei lead to chains of sequential a decays to longer lived daughter nuclei lying closer to the line of stability, some of which have surprisingly long half-lives. As an example, the decay of 115, produced in the AmC Ca,3n) reaction, results in a chain of a-emitting superheavy nuclei that culminates in Db (Z = 105), a nuclide with a half-life of one day [285, 286, 330]. This nuclide contains 7 neutrons more than the heaviest dubnium isotope that can be produced by either cold fusion or more asymmetric hot-fusion reactions. 

It was emphasized in [1] that the nuclear decay properties of the isotope to be used in these studies must be well known and have unique decay characteristics suitable for detection and positive identification on an atom-at-a-time basis in order to verify that it is from the element whose chemistry is to be studied It must have a half-life comparable to the proposed chemical separation procedure as well as a reasonable production and detection rate to permit statistically significant results to be obtained, and must give the same results for a few atoms as for macro amounts. For the transactinide elements, production rates range from a few atoms per minute for rutherfordium (Rf, Z = 104) to only about one atom per day in the case of elements 108 (hassium, Hs), 112, and 114, the heaviest elements studied to date with chemical techniques. Details of these chemical investigations are outlined in Liquid-Phase Chemistry of Superheavy Elements and Gas-Phase Chemistry of SuperheavyElements . 

Already the synthesis of heavy and superheavy elements is, from the technological point of view, very demanding. In order to gain access to the longer-lived isotopes of transactinide elements, exotic, highly radioactive target nuclides such as " Pu, " Am, or " Es are bombarded with intense heavy... 

Early on, gas-phase chemical separations played an important role in the investigation of the chemical properties of transactinide elements. The technique was pioneered by Zvara et al. at the Dubna laboratory and involved first chemical studies of volatile Rf, Db, and Sg halides and/or oxyhalides [105-107] see Gas-Phase Chemistry of Superheavy Elements for a detailed discussion. The experimental set-ups and the techniques involved are presented in Sect. 4.2. A new technique, named OLGA (On-line Gas chromatography Apparatus), which allowed the a-spectrometric measurement of final products, developed by Gaggeler et al. [108] was then successful in studying volatile transactinide compounds from Rf up to Bh [109-112], see Gas-Phase Chemistry of Superheavy Elements for a detailed discussion. In all these experiments, the isolated transactinide nuclides... 

The discovery of new chemical elements - the transactinides or superheavy elements - stimulated the work on theoretical predictions of their chemical properties. Our intention is to present empirical methods [20-35], which can be used to predict chemical properties and which are relevant to gas phase chemical studies of transactinides. 

The transactinides are the doorway to the superheavy elements. The region of shell stabilization starts here (O Fig. 19.1) without which the chart of the nuclides would end around seaborgium. For this reason, these elements are sometimes also referred to as "superheavy nuclei. In this chapter the conventional definition will be adopted when referring to the superheavy elements spherical nuclei that he around the next double shell closure above Pb. 

Nuclear Structure of the Transactinide Nuclides 19.4.1 Superheavy Elements The Limits of Stability... 

The separation techniques described in Chaps. 52 and 53 of Vol. 5 are really fast. Fast separation is also a crucial requirement for the identification of transuranic/transactinide and superheavy elements as discussed in Chaps. 18-21 of Vol. 2 (p. 1585). 

Hot-fusion reactions were employed in the discoveries of the elements beyond mendelevium as far as element 106, producing the first three members of the domain of superheavy elements. Higher transactinides have also been synthesized in these reactions. As before, the general trends with increasing atomic number were shorter half-lives and smaller production cross sections, a consequence of decreased survival probability in the evaporation process [132, 133]. The probability of decay from the nuclear ground state by spontaneous fission became significant in these elements. The techniques used in the experiments still included radiochemistry and off-line radiation counting [134]. As half-lives dropped below minutes into seconds it became more common to use direct techniques like transportation in gas jets to mechanisms like wheels and tapes (see Sect. 3.3 and Experimental Techniques ). Detection of new nuclides resulted from the detailed... 

Malli, G.L. Thirty years of relativistic self-consistent field theory for molecules Relativistic and electron correlation effects for atomic and molecular systems of transactinide superheavy elements up to ekaplutonium E126 with g-atomic spinors in the ground state configuration. Theor. Chem. Ace. 118, 473 82 (2007)... 

Studies of the chemical properties of the heaviest actinides (Z > 101) and aU of the transactinides (Z > 103), including superheavy elements (SHEs), depend on the use of atom-at-a-time chemistry. They cannot be produced by simple neutron... 

Isotopes of heaviest actinides and transactinides are characterized by short half-lives and low production cross sections see Synthesis of Superheavy Elements . Study of their chemical properties is therefore a real challenge [1, 7]. It should be... 

---