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Einsteinium is a synthetic chemical element; it has Chemical symbol Es and atomic number 99 and is a member of the actinide series and the seventh transuranium element.
Einsteinium was discovered as a component of the debris of the Ivy Mike explosion in 1952. Its most common isotope, einsteinium-253 (Es; half-life 20.47 days), is produced artificially from decay of californium-253 in a few dedicated high-power with a total yield on the order of one milligram per year. The reactor synthesis is followed by a complex process of separating einsteinium-253 from other actinides and products of their decay. Other isotopes are synthesized in various laboratories, but in much smaller amounts, by bombarding heavy actinide elements with light ions. Due to the small amounts of einsteinium produced and the short half-life of its most common isotope, there are no practical applications for it except basic scientific research. In particular, einsteinium was used to synthesize, for the first time, 17 atoms of the new element mendelevium in 1955.
Einsteinium is a soft, silvery, paramagnetic metal. Its chemistry is typical of the late actinides, with a preponderance of the +3 oxidation state; the +2 oxidation state is also accessible, especially in solids. The high radioactivity of Es produces a visible glow and rapidly damages its crystalline metal lattice, with released heat of about 1000 per gram. Studying its properties is difficult due to Es's decay to berkelium-249 and then californium-249 at a rate of about 3% per day. The longest-lived isotope of einsteinium, Es (half-life 471.7 days) would be more suitable for investigation of physical properties, but it has proven far more difficult to produce and is available only in minute quantities, not in bulk. Einsteinium . periodic.lanl.gov Einsteinium is the element with the highest atomic number which has been observed in macroscopic quantities in its pure form as einsteinium-253.
Like all synthetic transuranium elements, isotopes of einsteinium are very radioactive and are considered highly dangerous to health on ingestion.
Ghiorso and co-workers analyzed filter papers which had been flown through the explosion cloud on airplanes (the same sampling technique that had been used to discover Pu).Seaborg, p. 39 Larger amounts of radioactive material were later isolated from coral debris of the atoll, and these were delivered to the U.S. The separation of suspected new elements was carried out in the presence of a citric acid/ammonium buffer solution in a weakly acidic medium (pH ≈ 3.5), using ion exchange at elevated temperatures; fewer than 200 atoms of einsteinium were recovered in the end. Nevertheless, element 99, einsteinium, and in particular Es, could be detected via its characteristic high-energy alpha decay at 6.6 MeV. It was produced by the neutron capture of 15 by uranium-238 nuclei followed by seven beta decays, and had a half-life of 20.5 days. Such multiple neutron absorption was made possible by the high neutron flux density during the detonation, so that newly generated heavy isotopes had plenty of available neutrons to absorb before they could disintegrate into lighter elements. Neutron capture initially raised the mass number without changing the atomic number of the nuclide, and the concomitant beta-decays resulted in a gradual increase in the atomic number:
Some U atoms, however, could absorb two additional neutrons (for a total of 17), resulting in Es, as well as in the Fm isotope of another new element, fermium.Es, Fm and Fm would not be produced because of lack of beta decay in Cf and Es The discovery of the new elements and the associated new data on multiple neutron capture were initially kept secret on the orders of the U.S. military until 1955 due to Cold War tensions and competition with Soviet Union in nuclear technologies. However, the rapid capture of so many neutrons would provide needed direct experimental confirmation of the r-process multi-neutron absorption needed to explain the cosmic nucleosynthesis (production) of certain heavy elements (heavier than nickel) in , before beta decay. Such a process is needed to explain the existence of many stable elements in the universe. (pbk.) pp. 267.
Meanwhile, isotopes of element 99 (as well as of new element 100, fermium) were produced in the Berkeley and Argonne laboratories, in a nuclear fusion between nitrogen-14 and uranium-238, and later by intense neutron irradiation of plutonium or californium:
These results were published in several articles in 1954 with the disclaimer that these were not the first studies that had been carried out on the elements. The Berkeley team also reported some results on the chemical properties of einsteinium and fermium. Radiation Laboratory, University of California, Berkeley, UCRL-2591 The Ivy Mike results were declassified and published in 1955.
In their discovery of elements 99 and 100, the American teams had competed with a group at the Nobel Institute for Physics, Stockholm, Sweden. In late 1953 – early 1954, the Swedish group succeeded in synthesizing light isotopes of element 100, in particular Fm, by bombarding uranium with oxygen nuclei. These results were also published in 1954. Nevertheless, the priority of the Berkeley team was generally recognized, as its publications preceded the Swedish article, and they were based on the previously undisclosed results of the 1952 thermonuclear explosion; thus the Berkeley team was given the privilege to name the new elements. As the effort which had led to the design of Ivy Mike was codenamed Project PANDA, element 99 had been jokingly nicknamed "Pandemonium" but the official names suggested by the Berkeley group derived from two prominent scientists, Einstein and Fermi: "We suggest for the name for the element with the atomic number 99, einsteinium (symbol E) after Albert Einstein and for the name for the element with atomic number 100, fermium (symbol Fm), after Enrico Fermi." Both Einstein and Fermi died between the time the names were originally proposed and when they were announced. The discovery of these new elements was announced by Albert Ghiorso at the first Geneva Atomic Conference held on 8–20 August 1955. The symbol for einsteinium was first given as "E" and later changed to "Es" by IUPAC.Haire, p. 1577.
Unlike the lighter actinides californium, berkelium, curium and americium, which crystallize in a double hexagonal structure at ambient conditions; einsteinium is believed to have a face-centered cubic ( fcc) symmetry with the space group Fm m and the lattice constant . However, there is a report of room-temperature hexagonal einsteinium metal with and , which converted to the fcc phase upon heating to 300 °C.
The self-damage induced by the radioactivity of einsteinium is so strong that it rapidly destroys the crystal lattice, and the energy release during this process, 1000 watts per gram of 253Es, induces a visible glow.Haire, p. 1579 These processes may contribute to the relatively low density and melting point of einsteinium. draft manuscript Further, due to the small size of available samples, the melting point of einsteinium was often deduced by observing the sample being heated inside an electron microscope.Seaborg, p. 61 Thus, surface effects in small samples could reduce the melting point.
The metal is trivalent and has a noticeably high volatility. In order to reduce the self-radiation damage, most measurements of solid einsteinium and its compounds are performed right after thermal annealing.Seaborg, p. 52 Also, some compounds are studied under the atmosphere of the reductant gas, for example HO+HCl for EsOCl so that the sample is partly regrown during its decomposition.
Apart from the self-destruction of solid einsteinium and its compounds, other intrinsic difficulties in studying this element include scarcity – the most common Es isotope is available only once or twice a year in sub-milligram amounts – and self-contamination due to rapid conversion of einsteinium to berkelium and then to californium at a rate of about 3.3% per day:Seaborg, p. 55
Thus, most einsteinium samples are contaminated, and their intrinsic properties are often deduced by extrapolating back experimental data accumulated over time. Other experimental techniques to circumvent the contamination problem include selective optical excitation of einsteinium ions by a tunable laser, such as in studying its luminescence properties.Seaborg, p. 76
Magnetic properties have been studied for einsteinium metal, its oxide and fluoride. All three materials showed Curie–Weiss paramagnetic behavior from liquid helium to room temperature. The effective magnetic moments were deduced as for EsO and for the EsF, which are the highest values among actinides, and the corresponding Curie temperatures are 53 and 37 K.
The transuranic elements up to fermium, including einsteinium, should have been present in the natural nuclear fission reactor at Oklo, but any quantities produced then would have long since decayed away.
The first microscopic sample of Es sample weighing about 10 was prepared in 1961 at HFIR. A special magnetic balance was designed to estimate its weight.Hoffman, Darleane C.; Ghiorso, Albert and Seaborg, Glenn Theodore (2000) The Transuranium People: The Inside Story, Imperial College Press, pp. 190–191, . Larger batches were produced later starting from several kilograms of plutonium with the einsteinium yields (mostly Es) of 0.48 milligram in 1967–1970, 3.2 milligrams in 1971–1973, followed by steady production of about 3 milligrams per year between 1974 and 1978.Seaborg, pp. 36–37 These quantities however refer to the integral amount in the target right after irradiation. Subsequent separation procedures reduced the amount of isotopically pure einsteinium roughly tenfold.
Es (half-life 4.55 min) was produced by irradiating Am with carbon or U with nitrogen ions.Harry H. Binder: Lexikon der chemischen Elemente, S. Hirzel Verlag, Stuttgart 1999, , pp. 18–23. The latter reaction was first realized in 1967 in Dubna, Russia, and the involved scientists were awarded the Lenin Komsomol Prize. Эйнштейний (in Russian, a popular article by one of the involved scientists)
Es was produced by irradiating Cf with deuterium ions. It mainly β-decays to Cf with a half-life of minutes, but also releases 6.87-MeV α-particles; the ratio of β's to α-particles is about 400.
Es were obtained by bombarding Bk with α-particles. One to four neutrons are released, so four different isotopes are formed in one reaction.
Es was produced by irradiating a 0.1–0.2 milligram Cf target with a thermal neutron flux of (2–5)×10 neutrons/(cm·s) for 500–900 hours:
In 2020, scientists at ORNL created about 200 nanograms of Es; allowing some chemical properties of the element to be studied for the first time.
The atmospheric results were supplemented by the underground test data accumulated in the 1960s at the Nevada Test Site, as it was hoped that powerful explosions in a confined space might give improved yields and heavier isotopes. Apart from traditional uranium charges, combinations of uranium with americium and thorium have been tried, as well as a mixed plutonium-neptunium charge, but they were less successful in terms of yield and was attributed to stronger losses of heavy isotopes due to enhanced fission rates in heavy-element charges. Product isolation was problematic as the explosions were spreading debris through melting and vaporizing the surrounding rocks at depths of 300–600 meters. Drilling to such depths to extract the products was both slow and inefficient in terms of collected volumes.Seaborg, p. 40
Of the nine underground tests between 1962 and 1969,These were codenamed: "Anacostia" (5.2 TNT equivalent, 1962), "Kennebec" (<5 kilotons, 1963), "Par" (38 kilotons, 1964), "Barbel" (<20 kilotons, 1964), "Tweed" (<20 kilotons, 1965), "Cyclamen" (13 kilotons, 1966), "Kankakee" (20-200 kilotons, 1966), "Vulcan" (25 kilotons, 1966) and "Hutch" (20-200 kilotons, 1969) United States Nuclear Tests July 1945 through September 1992 , DOE/NV--209-REV 15, December 2000. the last one was the most powerful and had the highest yield of transuranics. Milligrams of einsteinium that would normally take a year of irradiation in a high-power reactor, were produced within a microsecond. However, the major practical problem of the entire proposal was collecting the radioactive debris dispersed by the powerful blast. Aircraft filters adsorbed only ~4 of the total amount, and collection of tons of corals at Enewetak Atoll increased this fraction by only two orders of magnitude. Extraction of about 500 kilograms of underground rocks 60 days after the Hutch explosion recovered only ~1 of the total charge. The amount of transuranic elements in this 500-kg batch was only 30 times higher than in a 0.4-kg rock picked up 7 days after the test which showed the highly non-linear dependence of the transuranics yield on the amount of retrieved radioactive rock.Seaborg, p. 43 Shafts were drilled at the site before the test in order to accelerate sample collection after explosion, so that explosion would expel radioactive material from the epicenter through the shafts and to collecting volumes near the surface. This method was tried in two tests and instantly provided hundreds of kilograms of material, but with actinide concentration 3 times lower than in samples obtained after drilling. Whereas such method could have been efficient in scientific studies of short-lived isotopes, it could not improve the overall collection efficiency of the produced actinides.Seaborg, p. 44
Though no new elements (except einsteinium and fermium) could be detected in the nuclear test debris, and the total yields of transuranics were disappointingly low, these tests did provide significantly higher amounts of rare heavy isotopes than previously available in laboratories.Seaborg, p. 47
Trivalent actinides can be separated from lanthanide fission products by a cation-exchange resin column using a 90% water/10% ethanol solution saturated with hydrochloric acid (HCl) as eluant. It is usually followed by anion-exchange chromatography using 6 molar HCl as eluant. A cation-exchange resin column (Dowex-50 exchange column) treated with ammonium salts is then used to separate fractions containing elements 99, 100 and 101. These elements can be then identified simply based on their elution position/time, using α-hydroxyisobutyrate solution (α-HIB), for example, as eluant.
The 3+ actinides can also be separated via solvent extraction chromatography, using bis-(2-ethylhexyl) phosphoric acid (abbreviated as HDEHP) as the stationary organic phase, and nitric acid as the mobile aqueous phase. The actinide elution sequence is reversed from that of the cation-exchange resin column. The einsteinium separated by this method has the advantage to be free of organic complexing agent, as compared to the separation using a resin column.
However, owing to its low melting point and high rate of self-radiation damage, einsteinium has a higher vapor pressure than lithium fluoride. This makes this reduction reaction rather inefficient. It was tried in the early preparation attempts and quickly abandoned in favor of reduction of einsteinium(III) oxide with lanthanum metal:Haire, p. 1590
| +Crystal structure and lattice constants of some Es compounds !Compound!!Color !! Symmetry!!Space group!!No!!Pearson symbol | a (picometre)!! b (pm)!! c (pm) |
| 880 | |
| 600 | |
| 410 | |
| 681 | |
| 2084 | |
| 670.2 |
Einsteinium(III) fluoride (EsF) can be precipitated from Es(III) chloride solutions upon reaction with fluoride ions. An alternative preparation procedure is to exposure Es(III) oxide to chlorine trifluoride (ClF) or F gas at a pressure of 1–2 atmospheres and temperature 300–400°C. The EsF crystal structure is hexagonal, as in californium(III) fluoride (CfF) where the Es ions are 8-fold coordinated by fluorine ions in a bicapped trigonal prism arrangement.Greenwood, p. 1270
Es(III) chloride (EsCl) can be prepared by annealing Es(III) oxide in the atmosphere of dry hydrogen chloride vapors at about 500°C for some 20 minutes. It crystallizes upon cooling at about 425°C into an orange solid with a hexagonal structure of UCl type, where einsteinium atoms are 9-fold coordinated by chlorine atoms in a tricapped trigonal prism geometry.Miasoedov, B. F. Analytical chemistry of transplutonium elements, Wiley, 1974 (Original from the University of California), , p. 99 Einsteinium(III) bromide (EsBr) is a pale-yellow solid with a monoclinic structure of AlCl type, where the einsteinium atoms are octahedrally coordinated by bromine (coordination number 6).
The divalent compounds of einsteinium are obtained by reducing the trivalent halides with hydrogen: manuscript draft
Einsteinium(II) chloride (EsCl),Fellows, R.L.; Young, J.P.; Haire, R.G. and Peterson J.R. (1977) in: GJ McCarthy and JJ Rhyne (eds) The Rare Earths in Modern Science and Technology, Plenum Press, New York, pp. 493–499. einsteinium(II) bromide (EsBr),Young, J.P.; Haire R.G., Fellows, R.L.; Noe, M. and Peterson, J.R. (1976) "Spectroscopic and X-Ray Diffraction Studies of the Bromides of Californium-249 and Einsteinium-253", in: W. Müller and R. Lindner (eds.) Plutonium 1975, North Holland, Amsterdam, pp. 227–234. and einsteinium(II) iodide (EsI) have been produced and characterized by optical absorption, with no structural information available yet.
Known oxyhalides of einsteinium include EsOCl, EsOBr and EsOI. These salts are synthesized by treating a trihalide with a vapor mixture of water and the corresponding hydrogen halide: for example, EsCl + HO/HCl to obtain EsOCl.Seaborg, p. 60
Luminescence of Es ions was however observed in inorganic hydrochloric acid solutions as well as in organic solution with di(2-ethylhexyl)orthophosphoric acid. It shows a broad peak at about 1064 nanometers (half-width about 100 nm) which can be resonantly excited by green light (ca. 495 nm wavelength). The luminescence has a lifetime of several microseconds and the quantum yield below 0.1%. The relatively high, compared to lanthanides, non-radiative decay rates in Es were associated with the stronger interaction of f-electrons with the inner Es electrons.
In 1955, mendelevium was synthesized by irradiating a target consisting of about 10 atoms of Es in the 60-inch cyclotron at Berkeley Laboratory. The resulting Es(α,n)Md reaction yielded 17 atoms of the new element with the atomic number of 101.
The rare isotope Es is favored for production of superheavy elements due to its large mass, relatively long half-life of 270 days, and availability in significant amounts of several micrograms. Hence Es was used as a target in the attempted synthesis of ununennium (element 119) in 1985 by bombarding it with calcium-48 ions at the superHILAC linear particle accelerator at Berkeley, California. No atoms were identified, setting an upper limit for the cross section of this reaction at 300 nanobarns.
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