Synthesis of elements

Such reactions are discussed at appropriate points throughout the book as each individual compound is being considered. A particularly important set of reactions in this category is the synthesis of element hydrides by hydrolysis of certain sulfides (to give H2S), nitrides (to give NH3), phosphides (PH3), carbides (C Hm), borides (B Hm), etc. Useful reviews are available on hydrometallurgy (the recovery of metals by use of aqueous solutions at relatively low temperatures), hydrothermal syntheses and the use of supercritical water as a reaction medium for chemistry. 

In the early years of this century the periodic table ended with element 92 but, with J. Chadwick s discovery of the neutron in 1932 and the realization that neutron-capture by a heavy atom is frequently followed by j6 emission yielding the next higher element, the synthesis of new elements became an exciting possibility. E. Fermi and others were quick to attempt the synthesis of element 93 by neutron bombardment of but it gradually became evident that the main result of the process was not the production of element 93 but nuclear fission, which produces lighter elements. However, in 1940, E. M. McMillan and P. H. Abelson in Berkeley, California, were able to identify, along with the fission products, a short-lived isotope of... 

Since the radioactive half-lives of the known transuranium elements and their resistance to spontaneous fission decrease with increase in atomic number, the outlook for the synthesis of further elements might appear increasingly bleak. However, theoretical calculations of nuclear stabilities, based on the concept of closed nucleon shells (p. 13) suggest the existence of an island of stability around Z= 114 and N= 184. Attention has therefore been directed towards the synthesis of element 114 (a congenor of Pb in Group 14 and adjacent superheavy elements, by bombardment of heavy nuclides with a wide range of heavy ions, but so far without success. 

The first (inconclusive) work bearing on the synthesis of element 104 was published by the Dubna group in 1964. However, the crucial Dubna evidence (1969-70) for the production of element 104 by bombardment of 94PU with loNe came after the development of a sophisticated method for rapid in situ chlorination of the product atoms followed by their gas-chromatographic separation on an atom-by-atom basis. This was a heroic enterprise which combined cyclotron nuclear physics and chemical separations. As we have seen, the actinide series of elements ends with 103 Lr. The next element should be in Group 4 of the transition elements, i.e. a heavier congenor of Ti, Zr and Hf. As such it would be expected to have a chloride... 

From ancient times, humans have pondered what the universe is made of Early philosophers proposed fire, earth, water, and air either individually or in combination as the building blocks of nature. Lavoisier defined an element operationally as a substance that cannot be broken down chemically. Using this definition, the number of elements has increased from around 30 in Lavoisier s time to over 115 today. The initial search for elements involved classical methods such as replacement reactions, electrochemical separation, and chemical analysis. New methods such as spectroscopy greatly advanced the discovery of new elements during the twentieth century. The last half century has been marked by the synthesis of elements by humans. 

The Dubna researchers tried unsuccessfully for many months to repeat their apparent synthesis of element 114. Eventually, however, their persistence was rewarded with the sighting of a different isotope of element 114, with 174 neutrons and a lifetime of a few seconds. This time the researchers saw two separate decay events, making the sighting much more secure. Encouraged by this success, they changed the target material to califomium-248 and manufactured element 116, which decayed by alpha emission to element 114. 

One reaction proposed for the synthesis of element 110 is the reaction of 59Co with 209Bi at a laboratory energy of 295 MeV. Calculate the expected total reaction cross section. 

However, as indicated in Section 15.4, observations of the synthesis of elements 114 and 116 (and possibly element 118) have been reported with low ( pb) cross sections. In addition, instead of following the trends shown in Figure 15.10, the half-lives of the longest-lived known isotopes of elements 106-112 are reported to be approximately milliseconds to seconds, an enhancement of orders of magnitude in then- lifetimes. At present, none of these observations have been verified by independent measurements. 

The synthesis of element 95, americium (Am), was accomplished in 1945 by Seaborg, James, and Morgan ... 

The mechanism assumed here is equivalent to the previous proposal [62] of a-addition, with the added advantage of demonstrating the transition between two states defined by Z/N = 1 and r respectively. This proposed synthesis of elements is more economical than the widely accepted big-bang scenario that requires special hypothetical conditions for the production of... 

These experiments resulted in the identification of elements 107 to 112 at the Gesellschaft fur Schwerionenforschung, GSI, in Darmstadt, and in the recent synthesis of elements 114 and 116 at the Joint Institute for Nuclear Research, JINR, in Dubna. We also report on a search for element 118, which started in 1999 at Lawrence Berkeley National Laboratory, LBNL, in Berkeley. In subsequent sections a theoretical description follows discussing properties of nuclei in the region of SHEs and phenomena, which influence the yield for the synthesis of SHEs. Empirical descriptions of hot and cold fusion nuclear reaction systematic are outlined. Finally, a summary and outlook is given. 

The effect of Coulomb repulsion on the cross section starts to act severely for fusion reactions to produce elements beyond fermium. From there on a continuous decrease of cross section was measured from microbams for the synthesis of nobelium down to picobarns for the synthesis of element 112. Data obtained in reactions with Pb and Bi for the In-evaporation channel at low excitation energies of about 10-15 MeV (therefore named cold fusion) and in reactions with actinide targets at excitation energies of 35-45 MeV (hot fusion) for the 4n channel are plotted in Figure 7a and b, respectively. 

The experimental work of the last two decades has shown that cross sections for the synthesis of the heaviest elements decrease almost continuously. However, recent data on the synthesis of element 114 and 116 in Dubna using hot fusion seem to break this trend when the region of spherical superheavy elements is reached. Therefore a confirmation is urgently needed that the region of spherical SHEs has finally been reached and that the exploration of the island has started and can be performed even on a relatively high cross section level. 

Synthesis of element 107 by nuclear fusion (reproduced with permission from G. Herrmann, Angew. Chem., Int. Ed. Engl, 1988, 27, 1421). 

The original (1974) synthesis of element 106 by the Berkeley group was repeated there by a different team in 1993 ... 

The first transuranium elements were discovered at Berkeley, California, by G. T. Seaborg and his group, first reports about elements 104 to 106 came from Dubna, Russia, synthesis of elements 107 to 112 was first accomplished at Darmstadt, that of element 114 at Dubna, and that of elements 116 and 118 at Berkeley. With increasing atomic number the stability decreases appreciably to values of the order of milliseconds, and the question whether an island of higher stability may be reached at atomic munbers of about 114 (or 120 or 126) is still open. 

Recently, three more elements have been detected. Synthesis of element 114 was reported 1999 at Dubna by Oganessian et al. who irradiated plutonium with Ca. Formation of 114 was inferred from the following decay chain ... 

A Russian-American collaboration led by Yuri A. Lazerev of Dubna and Ronald W. Lougheed of the Lawrence Livermore National Laboratory announced in January 1995, the synthesis of element 110 by the reaction 9 Pu -b ilS —b 110 -b Sn at Dubna. 

Molybdenum disilicide is made by direct synthesis of elements in a powdered mixture. Forming (e.g. from plastic mass containing an organic plasticizer) is followed by sintering at 1600—1700 °C the last stage of sintering may be effected by direct resistance heating. 

Synthesis of elements has also occurred since 1940 all the transuranic elements from 93 to 106, as well as a vast array of radioisotopes of natural elements, have been created by nuclear bombardment of various types. See resin, synthetic semisynthetic. 

Because of the hazardous character of hydrofluoric acid and the difficult access to elemental fluorine itself, the development of organofluorine chemistry and the practical use of fluoroorganic compounds started relatively late in the 19th century (Table 1.1). The real breakthrough was the first synthesis of elemental fluorine by H. Moissan in 1886 [1]. 

A. S. Marggraf, repeated in 1771 by C. Scheele 1886 First synthesis of elemental fluorine by H. Moissan (Nobel Prize in 1906) by... 

A purely chemical synthesis of elemental fluorine was achieved by K. O. Christe in 1986 [10] (Scheme 1.1), just in time for the 100 year anniversary of Moissan s first electrochemical fluorine synthesis. Nevertheless, in his paper Christe remarks that all the basic know-how required for this work had already been available 50 years earlier. The key to his simple method is a displacement reaction between potassium hexafluoropermanganate [11] with the strongly fluorophilic Lewis acid antimony pentafluoride at 150 °C. 

Hoyle, F. On nuclear reactions occurring in very hot stars. 1. The synthesis of elements from carbon to nickel. Astrophysical Journal Supplement, 1 (1954), 121 16. 

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