Editing Einsteinium (section)

==Characteristics==

===Physical===
[[File:EinsteiniumGlow.JPG|thumb|left|upright|Glow due to the intense radiation from ~300 μg of {{sup|253}}Es<ref>[[#Haire|Haire]], p. 1580</ref>]]
Einsteinium is a synthetic, silvery, radioactive metal. In the [[periodic table]], it is located to the right of the actinide [[californium]], to the left of the actinide [[fermium]] and below the lanthanide [[holmium]] with which it shares many similarities in physical and chemical properties. Its density of 8.84&nbsp;g/cm{{sup|3}} is lower than that of californium (15.1&nbsp;g/cm{{sup|3}}) and is nearly the same as that of holmium (8.79&nbsp;g/cm{{sup|3}}), despite einsteinium being much heavier per atom than holmium. Einsteinium's melting point (860&nbsp;°C) is also relatively low – below californium (900&nbsp;°C), fermium (1527&nbsp;°C) and holmium (1461&nbsp;°C).<ref name="CRC">Hammond C. R. "The elements" in {{RubberBible86th}}</ref><ref name="HAIRE_1990">Haire, R. G. (1990) "Properties of the Transplutonium Metals (Am-Fm)", in: Metals Handbook, Vol.&nbsp;2, 10th edition, (ASM International, Materials Park, Ohio), pp. 1198–1201.</ref> Einsteinium is a soft metal, with a [[bulk modulus]] of only 15&nbsp;GPa, one of the lowest among non-[[alkali metal]]s.<ref name="h1591">[[#Haire|Haire]], p. 1591</ref>

Unlike the lighter actinides [[californium]], [[berkelium]], [[curium]] and [[americium]], which crystallize in a double [[hexagonal crystal family|hexagonal]] structure at ambient conditions; einsteinium is believed to have a [[Cubic crystal system|face-centered cubic]] (''fcc'') symmetry with the space group ''Fm''{{overline|3}}''m'' and the lattice constant {{nowrap|''a'' {{=}} 575&nbsp;pm}}. However, there is a report of room-temperature hexagonal einsteinium metal with {{nowrap|''a'' {{=}} 398 pm}} and {{nowrap|''c'' {{=}} 650 pm}}, which converted to the ''fcc'' phase upon heating to 300&nbsp;°C.<ref name="ev" />

The self-damage induced by the radioactivity of einsteinium is so strong that it rapidly destroys the crystal lattice,<ref name="g1268" /> and the energy release during this process, 1000 watts per gram of <sup>253</sup>Es, induces a visible glow.<ref name="h1579">[[#Haire|Haire]], p. 1579</ref> These processes may contribute to the relatively low density and melting point of einsteinium.<ref name="ES_METALL">{{cite journal|last1=Haire|first1=R. G.|last2=Baybarz|first2=R. D.|doi=10.1051/jphyscol:1979431|title=Studies of einsteinium metal|date=1979|pages=C4–101|volume=40|journal=Le Journal de Physique|s2cid=98493620 |url=http://hal.archives-ouvertes.fr/docs/00/21/88/27/PDF/ajp-jphyscol197940C431.pdf|access-date=2010-11-24|archive-date=2012-03-07|archive-url=https://web.archive.org/web/20120307233020/http://hal.archives-ouvertes.fr/docs/00/21/88/27/PDF/ajp-jphyscol197940C431.pdf|url-status=live}} [http://www.osti.gov/bridge/servlets/purl/6582609-SrTVod/6582609.pdf draft manuscript] {{Webarchive|url=https://web.archive.org/web/20190710170812/http://www.osti.gov/bridge/servlets/purl/6582609-SrTVod/6582609.pdf |date=2019-07-10 }}</ref> 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.<ref name="s61">[[#Seaborg|Seaborg]], p. 61</ref> Thus, surface effects in small samples could reduce the melting point.

The metal is trivalent and has a noticeably high volatility.<ref>{{cite journal|last1=Kleinschmidt|first1=Phillip D.|last2=Ward|first2=John W.|last3=Matlack|first3=George M.|last4=Haire|first4=Richard G.|title=Henry's Law vaporization studies and thermodynamics of einsteinium-253 metal dissolved in ytterbium|journal=The Journal of Chemical Physics|volume=81|issue=1|pages=473–477|date=1984|doi=10.1063/1.447328|bibcode = 1984JChPh..81..473K }}</ref> In order to reduce the self-radiation damage, most measurements of solid einsteinium and its compounds are performed right after thermal annealing.<ref name="s52">[[#Seaborg|Seaborg]], p. 52</ref> Also, some compounds are studied under the atmosphere of the reductant gas, for example H{{sub|2}}O+[[hydrogen chloride|HCl]] for EsOCl so that the sample is partly regrown during its decomposition.<ref name="s60" />

Apart from the self-destruction of solid einsteinium and its compounds, other intrinsic difficulties in studying this element include scarcity – the most common {{sup|253}}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:<ref name="ES_F3" /><ref name="ES2O3" /><ref name="s55">[[#Seaborg|Seaborg]], p. 55</ref>
:<chem>
^{253}_{99}Es ->[\alpha][20 \ce{d}] ^{249}_{97}Bk ->[\beta^-][314 \ce{d}] ^{249}_{98}Cf
</chem>

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.<ref name="s76">[[#Seaborg|Seaborg]], p. 76</ref>

Magnetic properties have been studied for einsteinium metal, its oxide and fluoride. All three materials showed [[Curie–Weiss law|Curie–Weiss]] [[paramagnetic]] behavior from [[liquid helium]] to room temperature. The effective magnetic moments were deduced as {{val|10.4|0.3|u=[[Bohr magneton|''μ''{{sub|B}}]]}} for Es{{sub|2}}O{{sub|3}} and {{val|11.4|0.3|u=''μ''{{sub|B}}}} for the EsF{{sub|3}}, which are the highest values among actinides, and the corresponding [[Curie temperature]]s are 53 and 37 K.<ref>{{cite journal|last1=Huray|first1=P.|last2=Nave|first2=S.|last3=Haire|first3=R.|title=Magnetism of the heavy 5f elements|journal=Journal of the Less Common Metals|volume=93|pages=293–300|date=1983|doi=10.1016/0022-5088(83)90175-3|issue=2}}</ref><ref>{{cite journal|last1=Huray|first1=Paul G.|last2=Nave|first2=S. E.|last3=Haire|first3=R. G.|last4=Moore|first4=J. R.|title=Magnetic Properties of Es{{sub|2}}O{{sub|3}} and EsF{{sub|3}}|journal=Inorganica Chimica Acta|volume=94|issue=1–3|pages=120–122|date=1984|doi=10.1016/S0020-1693(00)94587-0}}</ref>

===Chemical===
Like all actinides, einsteinium is rather reactive. Its trivalent [[oxidation state]] is most stable in solids and aqueous solution where it induces a pale pink color.<ref name="HOWI_1956">[[#Holleman|Holleman]], p. 1956</ref> The existence of divalent einsteinium is firmly established, especially in the solid phase; such +2 state is not observed in many other actinides, including [[protactinium]], [[uranium]], [[neptunium]], [[plutonium]], [[curium]] and [[berkelium]]. Einsteinium(II) compounds can be obtained, for example, by reducing einsteinium(III) with [[samarium(II) chloride]].<ref name="s53">[[#Seaborg|Seaborg]], p. 53</ref>

===Isotopes===
{{main|Isotopes of einsteinium}}
Eighteen isotopes and four [[nuclear isomer]]s are known for einsteinium, with [[mass number]]s 240–257.{{NUBASE2020|ref}} All are radioactive; the most stable one, {{sup|252}}Es, has half-life 471.7 days.<ref>{{cite journal|last1=Ahmad|first1=I.|title=Half-life of the longest-lived einsteinium isotope-252Es|journal=Journal of Inorganic and Nuclear Chemistry|volume=39|pages=1509–1511|date=1977|doi=10.1016/0022-1902(77)80089-4|issue=9|last2=Wagner|first2=Frank}}</ref> The next most stable isotopes are {{sup|254}}Es (half-life 275.7 days),<ref>{{cite journal|last1=McHarris|first1=William|last2=Stephens|first2=F.|last3=Asaro|first3=F.|last4=Perlman|first4=I.|title=Decay Scheme of Einsteinium-254|journal=Physical Review|volume=144|pages=1031–1045|date=1966|doi=10.1103/PhysRev.144.1031|issue=3|bibcode = 1966PhRv..144.1031M }}</ref> {{sup|255}}Es (39.8 days), and {{sup|253}}Es (20.47 days). All the other isotopes have half-lives shorter than 40 hours, most shorter than 30 minutes. Of the five isomers, the most stable is {{sup|254m}}Es with a half-life of 39.3 hours.{{NUBASE2020|ref}}

===Nuclear fission===
Einsteinium has a high rate of [[nuclear fission]] that results in a low [[critical mass]]. This mass is 9.89 kilograms for a bare sphere of {{sup|254}}Es, and can be lowered to 2.9 kg by adding a 30-centimeter-thick steel [[neutron reflector]], or even to 2.26 kg with a 20-cm-thick reflector made of water. However, even this small critical mass far exceeds the total amount of einsteinium isolated so far, especially of the rare {{sup|254}}Es.<ref name="irsn">Institut de Radioprotection et de Sûreté Nucléaire, [https://ec.europa.eu/energy/sites/ener/files/documents/20131018_trm_evaluation.pdf "Evaluation of nuclear criticality safety data and limits for actinides in transport"] {{Webarchive|url=https://web.archive.org/web/20160306031803/http://ec.europa.eu/energy/sites/ener/files/documents/20131018_trm_evaluation.pdf |date=2016-03-06 }}, p. 16.</ref>

===Natural occurrence===
Due to the short half-life of all isotopes of einsteinium, any [[Primordial nuclide|primordial]] einsteinium—that is, einsteinium that could have been present on Earth at its formation—has long since decayed. Synthesis of einsteinium from naturally-occurring uranium and thorium in the Earth's crust requires multiple neutron capture, an extremely unlikely event. Therefore, all einsteinium on Earth is produced in laboratories, high-power nuclear reactors, or [[nuclear testing]], and exists only within a few years from the time of the synthesis.<ref name="em" />

The transuranic elements [[americium]] to [[fermium]], including einsteinium, were once created in the [[natural nuclear fission reactor]] at [[Oklo]], but any quantities produced then would have long since decayed away.<ref name="emsley">{{cite book|last=Emsley|first=John|title=Nature's Building Blocks: An A-Z Guide to the Elements|edition=New|date=2011|publisher=Oxford University Press|location=New York, NY|isbn=978-0-19-960563-7}}</ref>

Einsteinium was theoretically observed in the spectrum of [[Przybylski's Star]].<ref>{{cite journal | doi=10.3103/S0884591308020049 | volume=24 |issue = 2| title=Identification of absorption lines of short half-life actinides in the spectrum of Przybylski's star (HD 101065) | journal=Kinematics and Physics of Celestial Bodies | pages=89–98| bibcode=2008KPCB...24...89G |year = 2008|last1 = Gopka|first1 = V. F.|last2 = Yushchenko|first2 = A. V.|last3 = Yushchenko|first3 = V. A.|last4 = Panov|first4 = I. V.|last5 = Kim|first5 = Ch.| s2cid=120526363 }}</ref> However, the lead author of the studies finding einsteinium and other short-lived actinides in Przybylski's Star, Vera F. Gopka, admitted that "the position of lines of the radioactive elements under search were simply visualized in synthetic spectrum as vertical markers because there are not any atomic data for these lines except for their wavelengths (Sansonetti et al. 2004), enabling one to calculate their profiles with more or less real intensities."<ref>{{cite journal |last1=Gopka |first1=V. F. |last2=Yushchenko |first2=Alexander V. |last3=Shavrina |first3=Angelina V. |last4=Mkrtichian |first4=David E. |last5=Hatzes |first5=Artie P. |last6=Andrievsky |first6=Sergey M. |last7=Chernysheva |first7=Larissa V. |title=On the radioactive shells in peculiar main sequence stars: the phenomenon of Przybylski's star. |journal=Proceedings of the International Astronomical Union |year=2005 |volume=2004 |pages=734–742 |doi=10.1017/S174392130500966X |s2cid=122474778 |doi-access=free }}</ref> The signature spectra of einsteinium's isotopes have since been comprehensively analyzed experimentally (in 2021),<ref>{{cite journal | doi=10.1103/PhysRevC.105.L021302 |title = Nuclear structure investigations of {{sup|253−255}}Es by laser spectroscopy |journal = Physical Review C |volume = 105 |year = 2022 |last1 = Nothhelfer |first1 = S. |last2 = Albrecht-Schönzart |first2 = Th.E. |last3 = Block |first3 = M. |last4 = Chhetri |first4 = P. |last5 = Düllmann |first5 = Ch.E. |last6 = Ezold |first6 = J.G. |last7 = Gadelshin |first7 = V. |last8 = Gaiser |first8 = A. |last9 = Giacoppo |first9 = F. |last10 = Heinke |first10 = R. |last11 = Kieck |first11 = T. |last12 = Kneip |first12 = N. |last13 = Laatiaoui |first13 = M. |last14 = Mokry |first14 = Ch. |last15 = Raeder |first15 = S. |last16 = Runke |first16 = J. |last17 = Schneider |first17 = F. |last18 = Sperling |first18 = J.M. |last19 = Studer |first19 = D. |last20 = Thörle-Pospiech |first20 = P. |last21 = Trautmann |first21 = N. |last22 = Weber |first22 = F. |last23 = Wendt |first23 = K.|s2cid = 246603539 |doi-access = free }}</ref> though there is no published research confirming whether the theorized einsteinium signatures proposed to be found in the star's spectrum match the lab-determined results.