transuranium elements


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transuranium elements,

in chemistry, radioactive elements with atomic numbers greater than that of uraniumuranium
, radioactive metallic chemical element; symbol U; at. no. 92; mass number of most stable isotope 238; m.p. 1,132°C;; b.p. 3,818°C;; sp. gr. 19.1 at 25°C;; valence +3, +4, +5, or +6.
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 (at. no. 92). All the transuranium elements of the actinide seriesactinide series,
a series of radioactive metallic elements in Group 3 of the periodic table. Members of the series are often called actinides, although actinium (at. no. 89) is not always considered a member of the series.
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 were discovered as synthetic radioactive isotopes at the Univ. of California at Berkeley or at Argonne National Laboratory; in order of increasing atomic number they are neptuniumneptunium
, radioactive chemical element; symbol Np; at. no. 93; mass number of most stable isotope 237; m.p. about 640°C;; b.p. 3,902°C; (estimated); sp. gr. 20.25 at 20°C;; valence +3, +4, +5, or +6. Neptunium is a ductile, silvery radioactive metal.
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, plutoniumplutonium
, radioactive chemical element; symbol Pu; at. no. 94; mass no. of most stable isotope 244; m.p. 641°C;; b.p. 3,232°C;; sp. gr. 19.84 at 20°C;; valence +3, +4, +5, or +6.
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, americiumamericium
, artificially produced radioactive chemical element; symbol Am; at. no. 95; mass no. of most stable isotope 243; m.p. about 1,175°C;; b.p. about 2,600°C;; sp. gr. 13.67 at 20°C;; valence +2, +3, +4, +5, or +6.
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, curiumcurium
, artificially produced radioactive chemical element; symbol Cm; at. no. 96; mass no. of most stable isotope 247; m.p. about 1,340°C;; b.p. 3,110°C;; sp. gr. 13.5 (calculated); valence +3, +4.
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, berkeliumberkelium
[from Berkeley], artificially produced radioactive chemical element; symbol Bk; at. no. 97; mass no. of most stable isotope 247; m.p. about 1,050°C;; b.p. about 2,590°C;; sp. gr. 14 (estimated); valence +3, +4.
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, californiumcalifornium
[from California], artificially produced, radioactive metallic chemical element; symbol Cf; at. no. 98; mass no. of most stable isotope 251; m.p. about 900°C;; b.p. about 1,470°C;; density unknown; valence +3.
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, einsteiniumeinsteinium
[for Albert Einstein], artificially produced radioactive chemical element; symbol Es; at. no. 99; mass no. of most stable isotope 252; m.p. about 860°C;; b.p. and sp. gr. unknown; valence +2, +3.
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, fermiumfermium
[for Enrico Fermi], artificially produced radioactive chemical element; symbol Fm; at. no. 100; mass no. of most stable isotope 257; m.p. 1,527°C;; b.p. and sp. gr. unknown; valence +2, +3. Fermium is a member of Group 3 of the periodic table.
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, mendeleviummendelevium
, artificially produced radioactive chemical element; symbol Md; at. no. 101; mass no. of most stable isotope 258; m.p. 827°C;; b.p. and sp. gr. unknown; valence +1, +2, +3. Mendelevium is a metal of the actinide series in Group 3 of the periodic table.
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, nobeliumnobelium
, artificially produced radioactive chemical element; symbol No; at. no. 102; mass no. of most stable isotope 259; m.p. 827°C;; b.p. and density unknown; valence +2, +3. It is a metal of the actinide series in Group 3 of the periodic table.
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, and lawrenciumlawrencium,
artificially produced radioactive chemical element; symbol Lr; at. no. 103; mass number of most stable isotope 262; m.p. about 1,627°C;; b.p. and sp. gr. unknown; valence +3.
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. Of these only neptunium and plutonium occur in nature; they are produced in minute amounts in the radioactive decay of uranium.

Much of the study of the transuranium elements has taken place at the Lawrence Berkeley National Laboratory (at Berkeley, Calif.) and at the Joint Institute for Nuclear Research in Dubna, Russia; workers at both locations share credit for the independent discovery of rutherfordiumrutherfordium
, artificially produced radioactive chemical element; symbol Rf; at. no. 104; mass number of most stable isotope 265; m.p., b.p., and sp. gr. unknown; valence +4.
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, dubniumdubnium
, artificially produced radioactive chemical element; symbol Db; at. no. 105; mass number of most stable isotope 268; m.p., b.p., and sp. gr. unknown; valence +5.
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, and seaborgiumseaborgium
, artificially produced radioactive chemical element; symbol Sg; at. no. 106; mass number of most stable isotope 271; m.p., b.p., sp. gr., and valence unknown. Situated in Group 6 of the periodic table, it is expected to have properties similar to those of tungsten.
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 (at. no. 104 through 106), which are the first three transactinide elementstransactinide elements
, in chemistry, elements with atomic numbers greater than that of lawrencium (at. no. 103), the last member of the actinide series. See transuranium elements.
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. A German team at the Institute for Heavy Ion Research at Darmstadt discovered bohriumbohrium
, artificially produced radioactive chemical element; symbol Bh; at. no. 107; mass number of most stable isotope 270; m.p., b.p., sp. gr., and valence unknown. Situated in Group 7 of the periodic table, it is expected to have properties similar to those of the rare metal
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, hassiumhassium
, artificially produced radioactive chemical element; symbol Hs; at. no. 108; mass number of most stable isotope 277; m.p., b.p., sp. gr., and valence unknown. Situated in Group 8 of the periodic table, it is expected to have properties similar to those of osmium.
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, meitneriummeitnerium
, artificially produced radioactive chemical element; symbol Mt; at. no. 109; mass number of most stable isotope 276; m.p., b.p., sp. gr., and valence unknown. Situated in Group 9 of the periodic table it is expected to have properties similar to those of iridium.
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, darmstadtiumdarmstadtium,
artificially produced radioactive chemical element; symbol Ds; at. no. 110; mass number of most stable isotope 281; m.p., b.p., sp. gr., and valence unknown. Situated in Group 10 of the periodic table, it is expected to have properties similar to those of platinum.
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, roentgeniumroentgenium,
artificially produced radioactive chemical element; symbol Rg; at. no. 111; mass number of most stable isotope 280; m.p., b.p., sp. gr., and valence unknown. Situated in Group 11 of the periodic table, it is expected to have properties similar to those of gold.
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, and coperniciumcopernicium,
artificially produced radioactive chemical element; symbol Cn; at. no. 112; mass number of most stable isotope 285; m.p., b.p., sp. gr., and valence unknown.
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 (at. no. 107 through 112). Researchers at Japan's RIKEN Linear Accelerator Facility in Wako have been credited with the discovery of nihoniumnihonium
, artificially produced radioactive chemical element; symbol Nh; at. no. 113; mass number of most stable isotope 284; m.p., b.p., sp. gr., and valence unknown. Situated in Group 13 of the periodic table, it is expected to have properties similar to those of thallium and
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 (at. no. 113). The Dubna laboratory, with assistance from Lawrence Livermore National Laboratory, Calif., synthesized fleroviumflerovium,
artificially produced radioactive chemical element; symbol Fl; at. no. 114; mass number of most stable isotope 289; m.p., b.p., sp. gr., and valence unknown. Situated in Group 14 of the periodic table, it is expected to have properties similar to those of lead and tin.
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, moscoviummoscovium
, artificially produced radioactive chemical element; symbol Mc; at. no. 115; mass number of most stable isotope 288; m.p., b.p., sp. gr., and valence unknown.
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, livermoriumlivermorium,
artificially produced radioactive chemical element; symbol Lv; at. no. 116; mass number of most stable isotope 292; m.p., b.p., sp. gr., and valence unknown.
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, and oganessonoganesson
, artificially produced radioactive chemical element; symbol Og; at. no. 118. Scientists from the Joint Institute for Nuclear Research in Dubna, Russia, and Lawrence Livermore National Laboratory in California collaborated in the discovery of oganesson in experiments
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 (at. no. 114 through 116 and 118); and, with assistance from Vanderbilt Univ. and the Oak Ridge National Laboratory, Tenn., tennessinetennessine
, artificially produced radioactive chemical element; symbol Ts; at. no. 117; mass number of most stable isotope 294; m.p., b.p., sp. gr., and valence unknown.
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 (at. no. 117). The Berkeley team claimed to have produced livermorium and oganesson, but later retracted the claim for after other laboratories failed to reproduce Berkeley's results and a reanalysis of their data did not show the production of the element.

Up to and including fermium (at. no. 100), the transuranium elements are produced by the capture of neutrons; the transfermium elements are synthesized by the bombardment of transuranium targets with light particles or, more recently, by projecting medium-weight elements at targets of other medium-weight elements (see also synthetic elementssynthetic elements,
in chemistry, radioactive elements that were not discovered occurring in nature but as artificially produced isotopes. They are technetium (at. no. 43), which was the first element to be synthesized, promethium (at. no. 61), astatine (at. no.
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).

Isotopes of the transuranium elements are radioactive because their large nuclei are unstable, and the transactinide, or superheavy, elements in particular have very short half-liveshalf-life,
measure of the average lifetime of a radioactive substance (see radioactivity) or an unstable subatomic particle. One half-life is the time required for one half of any given quantity of the substance to decay.
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. However, on the basis of theories of nuclear structure, physicists have predicted that certain transactinide elements may have relatively stable isotopes. For example, an isotope of flerovium with mass number 298 (comprising 114 protons and 184 neutrons) should be very stable and resemble lead in its chemical properties. However, the three isotopes of flerovium that are claimed to have been synthesized have fewer than the requisite 184 neutrons.

Bibliography

See G. T. Seaborg and W. D. Loveland, The Elements beyond Uranium (1990); L. R. Morss and J. Fuger, ed., Transuranium Elements (1992); G. T. Seaborg and A. Ghiorso, The Transuranium People (1999).

Transuranium Elements

 

chemical elements beyond uranium in D. I. Mendeleev’s periodic system of the elements, that is, elements with atomic number (Z) greater than or equal to 93. Fourteen transuranium elements are known.

Owing to the relatively rapid rate of their radioactive decay, these elements have not been retained in the earth’s crust in significant amounts. The age of the earth is about 5 × 109 years (yr), while the half-life (T1/2) of the longest-lived isotopes of the transuranium elements is less than 107 yr. In the period since the formation of the earth, transuranium elements, which were synthesized by nuclear reactions, have either completely decayed or have greatly reduced in quantity (by a factor up to 1012). Microscopic amounts of 244Pu, the longest-lived transuranium element (T1/2 ~ 8 × 106 yr), have been found in natural ores. This isotope possibly has remained in the earth since the time of the earth’s formation. Uranium ores have yielded traces of 237Np (T1/2 ~ 2.14 × 106 yr) and 239Pu (T1/2 ~ 2.4 × 104 yr), which were formed as a result of atomic reactions with the participation of uranium nuclei.

The first transuranium elements were synthesized in the early 1940’s in Berkeley (USA) by a group of scientists under the direction of E. McMillan and G. Seaborg, both of whom received a Nobel Prize for the discovery and study of these elements. There are several methods of synthesizing transuranium elements, all of which essentially reduce to the bombardment of targets with beams of neutrons or charged particles. When uranium is the target, powerful neutron beams produced in nuclear reactors or by the explosion of nuclear devices may be used to obtain the transuranium elements through fermium (Z = 100) inclusively. The synthesis process consists either in (1) the consecutive capture of neutrons, with each capture step accompanied by an increase in the mass number A, leading to beta decay and an increase in nuclear charge Z, or (2) the instantaneous capture of a large number of neutrons (by way of an explosion), with a long chain of beta-decay steps. The possibilities of this method are limited because of the insufficient density of neutron beams, the low probability of capturing a large number of neutrons, and, most important of all, the very rapid radioactive decay of nuclei with Z > 100, which precludes the obtainment of nuclei with Z > 100.

The element with Z = 101, Mendelevium, was discovered in 1955 by the bombardment of 25399Es with accelerated alpha particles. Five elements with Z > 101 were obtained in charged particle accelerators (the cyclotron of the Joint Institute for Nuclear Research at Dubna, USSR, and the Heavy Ion Linear Accelerator at Berkeley, USA) through nuclear reactions with accelerated heavy ions. The scientific groups under the direction of G. N. Flerov at Dubna and of Seaborg and A. Ghiorso at the Lawrence Radiation Laboratory in Berkeley have made the major contributions in this work. Significant results have also been obtained at the Oak Ridge National Laboratory in the USA.

Two types of nuclear reactions, namely, fusion and fission, are used for the synthesis of the heavier transuranium elements. In the first case, the nuclei of the target and the accelerated ion fuse completely and the excess energy of the excited compound nucleus is eliminated by neutron “evaporation.” Upon using ions of carbon, oxygen, and neon and targets of plutonium, curium, and californium, a highly excited compound nucleus is formed with excitation of about 40–60 megaelectron volts (MeV). Each evaporated neutron is capable of removing, on the average, energy of the order of 10–12 MeV from the nucleus, and consequently up to five neutrons must be ejected to “cool” the compound nucleus. For elements with Z = 104–105, the probability of the evaporation of one neutron is 500–100 times less than the probability of fission. This accounts for the low yield of new elements: the fraction of nuclei that “survive” as a result of the loss of excitation is only 10–8–10–10 of the total number of target nuclei that fuse with the particles. This accounts for the synthesis of only five new elements (Z = 102–106) in the past 20 years.

A new method, based on nuclear fusion, has been developed at the Joint Institute for Nuclear Research for the synthesis of transuranium elements. In this method, densely packed stable nuclei of lead isotopes are used as the target, and the relatively heavy ions of argon, titanium, and chromium as the bombarding particles. The excess energy of the ions is used for the “unpacking” of the compound nucleus; the excitation energy is low, only 10–15 MeV. The evaporation of one or two neutrons is sufficient to eliminate the excitation of such a nuclear system. As a result, a very noticeable gain in the yield of new transuranium elements has been obtained. This method was used to synthesize the transuranium elements with Z = 100, Z = 104, and Z = 106.

In 1965, Flerov proposed the method of induced fission using heavy ions for the synthesis of transuranium elements. Fragments resulting from such nuclear fission have a symmetrical distribution relative to mass and charge with a large dispersion; thus, elements with Z significantly greater than half the sum of Z of the target and Z of the bombarding ion may be observed in the fission fragments. The distribution of fission fragments was found experimentally to become broader with the use of heavier particles. The use of accelerated xenon or uranium ions would permit the production of new transuranium elements as heavy fission fragments upon the bombardment of uranium targets. In 1971 xenon ions were accelerated using two cyclotrons at the Joint Institute for Nuclear Research for the bombardment of a uranium target. The results indicated that this new method is suitable for the synthesis of heavy transuranium elements.

Transuranium elements undergo all types of radioactive decay. However, electron capture and beta decay are relatively slow processes, and their role becomes minor in the decay of nuclei with Z > 100, which have short lifetimes with respect to alpha decay and spontaneous fission. With increasing atomic number, the competition between spontaneous fission and beta decay becomes more significant. Instability with respect to spontaneous fission apparently determines the limit of the periodic system of the elements. While the half-life of 92U in spontaneous fission is about 1016 and of 94Pu about 1010 yr, the half-life for 100Fm is measured in hours, the half-life of element 104 (seeKURCHA-TOVIUM) is measured in seconds, and the half-life of element number 106 is only several milliseconds. (SeeACTINIDES for the chemical properties of transuranium elements to Z = 104 and the structure of their electron shells.)

Theory suggests that the existence of very heavy nuclei with enhanced stability with respect to spontaneous fission and alpha decay is possible. This “island of stability” should be located near the magic number nucleus, which has 114 protons and 184 neutrons. If this hypothetical region of stability is found to be real, then the limits of the periodic system of the elements will be expanded significantly, to which end work is under way in search of new experimental methods that would make possible the discovery of new elements. It is relatively simple to obtain 114 protons in a new nucleus but difficult to obtain 184 neutrons. Failure to reach the magic number 184 even by a few units sharply decreases the stability of a nucleus with respect to spontaneous fission.

Analysis of the fission barriers and lifetimes of the superheavy elements have indicated that some such elements, may have a half-life of about 1018 yr, and microscopic amounts of these elements may have been retained on the earth to the present time. In 1968 work was begun under the direction of Flerov to search for superheavy elements in nature. Terrestrial minerals, products of volcanic eruption, and geothermal waters are being investigated, as well as substances capable of accumulating the heavy component of cosmic rays (iron-manganese concretions from the ocean bottom, bottom silts of lakes and seas, meteorites, and lunar regolith). Samples in which theoretically there may be chemical elements with Z = 108 are being studied. At the same time research is being conducted using multicharged ion accelerators.

REFERENCES

Flerov, G. N., and I. Zvara. Khimicheskie elementy vtoroi sotni: Soobshcheniia Ollal D7–6013. [Dubna, 1971.]
Flerov, G. N. “Poisk i sintez transuranovykh elementov.” In Peaceful Uses of Atomic Energy, vol. 7. New York-Vienna, 1972. Page 471.
Radioaktivnye elementy Po(Ns)— . . . . Edited by I. V. Petrianov-Sokolov. Moscow, 1974.

G. N. FLEROV and V. A. DRUIN

transuranium elements

[¦tranz·yu̇′rā·nē·əm ′el·ə·məns]
(chemistry)
References in periodicals archive ?
Our prime objectives are to serve as a reference centre for basic actinide research, to contribute to an effective safety and safeguards system for the nuclear fuel cycle, and to study technological and medical applications of transuranium elements.
After the war, Seaborg and his colleagues continued their research on the transuranium elements, discovering such elements as berkelium, californium, einsteinium, fermium, mendelevium, and nobelium.
The waste will include transuranium elements, which have long half-life periods, the group said.
The Chemistry Nobelists Name Award Field Year Ernest Rutherford Disintegration of elements and chemistry 1908 of radioactive substances Marie Curie Discovery of radium and 1911 polonium Frederick Soddy Chemistry of radioactive 1921 substances and origin and nature of isotopes Francis Aston Discovery of isotopes of 1922 many elements by mass spectroscopy Harold Urey Discovery of heavy 1934 hydrogen Frederic Joliot & Synthesis of new radio- 1935 Irene Joliot-Curie active elements George de Hevesy Isotopes as tracers in 1943 chemical research Otto Hahn Discovery of atomic 1944 fission Glenn Seaborg & Discoveries of 1951 Edwin McMillan transuranium elements Willard Libby Development of radiocarbon dating 1960
Neptunium and plutonium were the first of the transuranium elements to be discovered.
of Chemistry of Transuranium Elements of the Russian Academy
Dewan came up with the name, a nod to the nuclear optimism of the 1950s and the transuranium elements that make nuclear power possible.
Progress in synthesis and in the study of the properties of the far transuranium elements has increased interest in the question of the upper limits of the Periodic Table.
Located at the Joint Research Centre's Institute for Transuranium Elements in Karlsruhe, Germany, the facilities cost Euro 10 million, paid for by the JRC.
McMillan for the discovery of plutonium and nine other transuranium elements.
Contract notice: Supply of air filters for the Institute for Transuranium Elements (ITU)
The other four institutes that make up the JRC are the Institute for Reference Materials and Measurement (IRMM) in Geel, Belgium), the Institute for Transuranium Elements (ITU) in Karlsruhe, Germany), the Institute for Health and Consumer Protection (IHCP) in Ispra, and the Institute for Prospective Technological Studies (in Seville, Spain).

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