Table XII

398 Pages·2005·30.61 MB·English

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Table of Contents
(Subject Area: Inorganic Chemistry)

Pages in the
Article Authors
Encyclopedia

Actinide Elements Siegfried Hübener Pages 211-236
Bioinorganic Brian T. Farrer and Vincent L.
Pages 117-139
Chemistry Pecoraro
Herbert Beall and Donald F.
Boron Hydrides Pages 301-316
Gaines
Coordination
R. D. Gillard Pages 739-760
Compounds
L. G. Christophorou and S. J.
Dielectric Gases Pages 357-371
Dale
Electron Transfer
Gilbert P. Haight, Jr. Pages 347-361
Reactions
Halogen Chemistry Marianna Anderson Busch Pages 197-222
Inclusion (Clathrate)
Jerry L. Atwood Pages 717-729
Compounds
Inorganic Exotic Joel F. Liebman, Kay Severin and
Pages 817-838
Molecules Thomas M. Klapötke
Liquid Alkali Metals C. C. Addison Pages 661-671
Main Group Russell L. Rasmussen, Joseph G.
Pages 1-30
Elements Morse and Karen W. Morse
Mesoporous
Robert Mokaya Pages 369-381
Materials, Synthesis
Metal Cluster
D. F. Shriver Pages 407-409
Chemistry
Metal Hydrides Holger Kohlmann Pages 441-458
Metal Particles and Allan W. Olsen and Kenneth J.
Pages 513-550
Cluster Compounds Klabunde
Nano sized Inorganic Leroy Cronin, Achim Müller and
Pages 303-317
Clusters Dieter Fenske
Noble Metals Hubert Schmidbaur and John L.
Pages 463-492
(Chemistry) Cihonski
Noble-Gas Chemistry Gary J. Schrobilgen Pages 449-461
Periodic Table
N. D. Epiotis and D. K. Henze Pages 671-695
(Chemistry)
Rare Earth Elements Zhiping Zheng and John E.
Pages 1-22
and Materials Greedan
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Actinide Elements
Siegfried Hu¨bener
ForschungszentrumRossendorf
I. Discovery,Occurrence,and
SynthesisoftheActinides
II. RadioactivityandNuclearReactionsofActinides
III. ApplicationsofActinides
IV. ActinideMetals
V. ActinideIons
VI. ActinideCompoundsandComplexes
GLOSSARY Speciation Characterization of physical and chemical
states of (actinide) species in a given (chemical)
Actinylion DioxoactinidecationsMO+andMO2+. environment.
2 2
Decaychain Aseriesofnuclidesinwhicheachmember Transactinide elements Artificial elements beyond the
transformsintothenextthroughnucleardecayuntila actinideelements,beginningwithrutherfordium(Rf),
stablenuclidehasbeenformed. element104.Theheaviestelements,synthesizeduntil
Lanthanides Fourteenelementswithatomicnumbers58 now, are the elements 114, 116, and 118. At present,
(cerium)to71(lutetium)thatarearesultoffillingthe bohrium (Bh), element 107, is the heaviest element
4f orbitalswithelectrons. which has been characterized chemically; chemical
Nuclear fission The division of a nucleus into two or studiesofelement108,hassium(Hs),andelement112
more parts, usually accompanied by the emission of areinpreparation.
neutronsandγ radiation.
Nuclide Aspeciesofatomcharacterizedbyitsmassnum-
ber, atomic number, and nuclear energy state. A ra- THE ACTINIDE ELEMENTS (actinoids) comprise the
dionuclideisaradioactivenuclide. 14 elements with atomic numbers 90–103, which fol-
Primordial radionuclides Nuclides which were pro- low actinium in the periodic table: thorium (Th), pro-
duced during element evolution and which have tactinium(Pa),uranium(U),neptunium(Np),plutonium
partly survived since then due to their long half- (Pu),americium(Am),curium(Cm),berkelium(Bk),cal-
lives. ifornium(Cf),einsteinium(Es),fermium(Fm),mendele-
Radioactivity Thepropertyofcertainnuclidesofshow- vium(Md),nobelium(No),andlawrencium(Lr).Theac-
ing radioactive decay in which particles or γ radia- tinides constitute a unique series of elements which are
tionareemittedorthenucleusundergoesspontaneous formedbytheprogressivefillingofthe5f electronshell.
fission. Although not formally an actinide element, actinium (Ac;
211
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212 ActinideElements
atomicnumber89)isusuallyincludedindiscussionsabout tainedbyreductionofitstetrachloridewithpotassiumhe
theactinides. namedthorium.(Later,in1841,B.Peligotusedthesame
AccordingtotheInternationalUnionofPureandAp- methodtoprepareuraniummetalforthefirsttime.)Tho-
plied Chemistry (IUPAC), the name actinoid is prefer- riumconstitutes8.1ppmoftheEarth’scrustandisthus
abletoactinidebecausetheending“-ide”normallyindi- as abundant as boron. Converted by neutron irradiation
catesanegativeion.However,owingtowidecurrentuse, to 233U, it could yield an amount of neutron-fissile ma-
“actinide”isstillallowed. terial several hundred times the amount of the naturally
occurringfissileuraniumisotope235U.Theprincipaltho-
riumoreismonazite,amixtureofrare-earthandthorium
I. DISCOVERY, OCCURRENCE, AND
phosphatescontainingupto30%ThO .Monazitesands
2
SYNTHESIS OF THE ACTINIDES
are widely distributed throughout the world. In Canada
thoriumisrecoveredfromuranothorite(amixedthorium-
A. NaturallyOccurringActinides uranium silicate accompanied by pitchblende) as a co-
productofuranium.Rarermineralsthorianite(90%ThO )
All of the isotopes of the actinide elements are radioac- 2
tive,andonlyfouroftheprimordialisotopes,232Th,235U, andthorite(ThSiO4;62%thorium)havebeenfoundinthe
238U,and244Pu,haveasufficientlonghalf-lifeforthereto westernUnitedStatesandNewzealand.Naturalthorium
is100%232Th.
beanyoftheseisotopesleftinnature.Onlythreeactinide
In1913protactiniumwasdiscoveredbyK.Fajansand
elementsandactiniumwereknownaslateas1940.Inad-
O.Go¨hring,whoidentified234mPaasanunstablemember
ditiontothoriumanduranium,protactiniumandactinium
ofthe238Udecayseries.Theynamedthenewelementbre-
havebeenfoundtoexistinuraniumandthoriumoresdue
tothe238U[Eq.(1)]and235U[Eq.(2)]decayseries: viumbecauseofitsshorthalf-lifeof1.15min.In1918the
longer-livedisotope231Pa,withahalf-lifeof32,800years,
−α −β− −β−
238U−→234Th−→234Pa−→234U, (1) wasidentifiedindependentlybytwogroups,O.Hahnand
92 90 91 92
L. Meitner, and F. Soddy and J. A. Cranston, as a prod-
235U−−→α 231Th−−→β− 231Pa−−→α 227Ac. (2) uctof235Udecay.Sincethenamebreviumwasobviously
92 90 91 89
inappropriate for such a long-lived radioelement, it was
Itwasnotuntil1971thattheexistenceofprimordial244Pu
changed to protactinium, thus naming element 91 as the
innatureintraceamountswasshownbyD.C.Hoffman
parent of actinium. Protactinium is one of the rarest of
andco-workers.
thenaturallyoccurringelements.Althoughnotworthex-
Uranium was the first actinide element to be discov-
tracting from uranium ores, protactinium becomes con-
ered.M.H.Klaprothshowedin1789thatpitchblendecon-
centratedinresiduesfromuraniumprocessingplants.
tainedanewelementandnamedituraniumafterthethen
Actinium was discovered by A. Debierne in 1899. Its
newlydiscoveredplanetUranus.Uraniumisnowknown
name is derived from the Greek word for beam or ray,
to comprise 2.1 ppm of the Earth’s crust, which makes
referring to its radioactivity. The natural occurrence of
itaboutasabundantasarsenicoreuropium.Itiswidely
thelongestlivedactiniumisotope227Ac,withahalf-life
distributed,withtheprincipalsourcesbeinginAustralia,
of 21.77 years, is entirely dependent on that of its pri-
Canada, South Africa, and the United States. The two
mordial ancestor, 235U. The natural abundance of 227Ac
most important oxide minerals of uranium are uraninite isestimatedtobe5.7·10−10ppm.Themostconcentrated
(U O ; 50–90% uranium), a variety of which is called
3 8 actiniumsampleeverpreparedfromanaturalrawmaterial
pitchblende,andcarnotite(K2(UO2)(VO4)2·3H2O;54% consisted of about 7 µg of 227Ac in less than 0.1 mg of
uranium). A very common uranium mineral is autu-
La O .
nite (Ca(UO ) (PO ) ·nH O, n=8–12). Natural ura- 2 3
2 2 4 2 2
niumconsistsof99.3%238Uand0.72%ofthefissionable
isotope 235U. A third important isotope, 233U, does not B. SyntheticActinides
occur in nature but can be produced by thermal-neutron
Stimulated by the discovery of the neutron in 1932 by
irradiationof232Th[Eq.(3)]:
J.Chadwickandthefirstsynthesisofartificialradioactive
−β− −β− nucleiusingαparticle-inducednuclearreactionsin1934
232Th+1n →233Th−→233Pa−→233U. (3)
90 0 90 91 92 by F. Joliot and I. Curie, many attempts were made to
This process converts thorium to fissionable fuel in a producetransuraniumelementsbyneutronirradiationof
breederreactor. uranium.In1934,E.FermiandlaterO.Hahn,L.Meitner,
ThoriumwasdiscoveredbyJ.J.Berzeliusin1828when andF.Strassmannreportedthattheyhadcreatedtransura-
heisolatedanewoxidefromaNorwegianorethenknown niumelements.Butin1938,O.HahnandF.Strassmann
asthorite.Henamedtheoxidethoria,andthemetalheob- showedthattheradioactivespeciesproducedbyneutron
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ActinideElements 213
irradiation of uranium were in fact fission fragments re- cium and curium failed, believing that they would have
sultingfromthenuclearfissionofuranium!Thus,theearly chemical properties similar to uranium, neptunium, and
searchfortransuraniumelementsledtooneofthegreatest plutonium. Once it was recognized that these elements,
discoveriesofthe20thcentury. accordingtoG.T.Seaborg’sactinideconcept,mighthave
Thefirsttransuraniumelement,neptunium,wasdiscov- propertiessimilartoeuropiumandgadolinium,theuseof
eredin1940byE.M.McMillanandP.H.Abelson.They properchemicalproceduresledtosuccess.Byanalogyto
wereabletochemicallyseparateandidentifyelement93 europium (named after Europe) and gadolinium (named
formedinthefollowingreactionsequences[Eq.(4)]: afterJohanGadolin,aFinnishrare-earthchemist),forel-
ements95and96thenamesamericiumafterthecontinent
−β− −β−
238U+1n →239U−−→239Np−−−→239Pu. (4) ofAmericaandcuriumtohonorPierreandMarieCurie
92 0 92 93 94
23min 2.3days were proposed. The elements with the atomic numbers
Theyshowedthatelement93haschemicalpropertiessim- 97 and 98 at first could not be produced by irradiation
ilartothoseofuraniumandnotthoseofaneka-rheniumas with neutrons, because β− decaying isotopes of curium
suggestedonthebasisoftheperiodictableofthattime.To were not known. By 1949 sufficient amounts of 241Am
distinguish it from uranium, element 93 was reduced by and 242Cm had been accumulated to make it possible to
SO andprecipitatedasafluoride.Thisnewelementwas produceelements97and98inhelium-ionbombardments.
2
namedneptuniumafterNeptune,theplanetdiscoveredaf- Theαparticle-emittingspeciesproducedinthebombard-
ter Uranus. In 1952, trace amounts of 237Np were found mentscouldbeidentifiedasisotopesofelements97and
in uranium of natural origin, formed by neutron capture 98, which were named berkelium and californium after
inuranium. thecityandstateofdiscovery.
It was obvious to the discoverers of neptunium that Elements99and100,namedeinsteiniumandfermium
239Np should β decay to the isotope of element 94 with to honor Albert Einstein and Enrico Fermi, were unex-
mass number 239, but they were unable to identify it. pectedlysynthesizedinthefirstU.S.thermonuclearex-
However, up to the end of 1940, G. T. Seaborg, E. M. plosionin1952.Thesuccessivecaptureofnumerousneu-
McMillan, J. W. Kennedy, and A. C. Wahl succeeded in trons by 238U and subsequent β− decay chains ended in
identifying238Puinuranium,whichwasbombardedwith theβ stablenuclides253Esand255Fm.Fromtonsofcoral
deuteronsproducedinthe60-in.cyclotronattheUniver- collectedattheexplosionarea,hundredsofatomsofthe
sityofCaliforniainBerkeley[Eq.(5)]: new elements could be separated and positively identi-
fied. Further attempts to produce still heavier elements
−β
238U+2H→21n+238Np −−−→ 238Pu. (5) in underground nuclear tests or in high-flux nuclear re-
92 1 0 93 94
2.1days actorsfailed.257Fmistheheaviestnuclidewhichcanbe
Element94wasnamedplutoniumaftertheplanetdiscov- produced using neutron-capture reactions, owing to the
eredlast,Pluto.In1941,thefirst0.5µgofthefissionable veryshorthalf-livesoftheheavierfermiumisotopesand
isotope239Puwereproducedbyirradiating1.2kgofuranyl their spontaneous fission instead of β− decay. To pro-
nitratewithcyclotron-generatedneutrons.In1948,trace duceelement101,mendelevium,onlyabout109atomsof
amountsof239Puwerefoundinnature,formedbyneutron 253Es were made available for a bombardment with he-
capture in uranium. In chemical studies, plutonium was lium ions in the Berkeley 60-in. cyclotron. For the first
showntohavepropertiessimilartouraniumandnottoos- timeanelementwasdiscoveredin“one-atom-at-a-time”
miumassuggestedearlier.Theactinideconceptadvanced experiments on the basis of only 17 produced atoms re-
by G. T. Seaborg, to consider the actinide elements as a coiling from the einsteinium target. The discoverers of
second f transition series analogous to the lanthanides, element 101, A. Ghiorso, B. G. Harvey, G. R. Choppin,
systematizedthechemistryofthetransuraniumelements S.G.Thompson,andG.T.Seaborg,suggestedthename
and facilitated the search for heavier actinide elements. mendelevium in honor of the Russian chemist Dmitri I.
The actinide elements americium (95) through fermium Mendeleev,whowasthefirsttouseaperiodicsystemof
(100)wereproducedfirsteithervianeutronorhelium-ion theelementstopredictthechemicalpropertiesofundis-
bombardments of actinide targets in the years between coveredelements.
1944and1955. The synthesis of element 102 was even more compli-
Element96,curium,wasproducedin1944bythebom- cated,becauseafermiumtargettoapplythebombardment
bardmentof239PuwithheliumionsintheBerkeley60-in. withheliumionswasnotavailable.Inordertomakeuseof
cyclotron,andsoonafteritwasfoundthat241Pu,formed lightertargetelements,heavierionshadtobeaccelerated.
from239Pubytwosuccessiveneutroncapturesinanuclear Thediscoveryofelement102wasfirstreportedin1957
reactor,decaysunderβ−particleemissiontogive241Am. by an international group working at the Nobel Institute
Earlierattemptstoproduceandchemicallyseparateameri- ofPhysicsinStockholm.Thenamenobeliuminhonorof
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214 ActinideElements
Alfred Nobel was immediately accepted by the IUPAC. is reduced by 2, the mass number by 4. With emission
However, experiments at Berkeley and the Kurchatov of a β− particle, the mass number remains unchanged,
Institute in Moscow showed that the original Swedish whereas the atomic number increases by 1. As a result,
claimtohavepreparedelement102wasinerror.Attempts inthesedecayseriesthemassnumbercandifferonlyby
to synthesize and identify isotopes of element 102 in multiples of 4 and there are four such families, desig-
heavy ion bombardments of actinide targets dragged on nated4n+0(thoriumseries),4n+1(neptuniumseries),
formanyyearsatthelaboratoriesinBerkeleyandDubna, 4n+2 (uranium or uranium-radium series), and 4n+3
Russia.Thus,scientistsfromBerkeleysuggestedthatthe (actiniumseries).Theneptuniumseriesismissinginna-
creditforthediscoveryshouldbeshared.But,in1993the ture. It was probably present in nature for some million
IUPAC-IUPAPTransfermiumWorkingGroupconcluded yearsafterthegenesisoftheelements,butdecayeddueto
thattheDubnalaboratoryfinallyachievedanundisputed therelativelyshorthalf-lifeof237Np,comparedwiththe
synthesis. ageoftheEarth(about5·109years).Eachseriescontains
Also,thediscoveryofelement103,thelastactinideel- a number of short-lived nuclides, and the final members
ement,wascontestedbyBerkeleyandDubnaforalong of each series are stable nuclides. α Decay is the domi-
time.AtBerkeleymixturesofcaliforniumisotopeswere nantdecaymodeoflong-livedheavynucleiwithatomic
bombardedwithboronions,whereasatDubnathebom- numbers Z>83.Withincreasingatomicnumbersspon-
bardmentofamericiumtargetswithoxygenionswasap- taneousfissionbeginstocompetewithαdecay.For238U
plied.Finally,bothgroupsacceptedtheconclusionofthe theprobabilityofspontaneousfissionisabout10−4%of
Transfermium Working Group, that full confidence was thatofαdecayandisalreadyabout90%for256Fm.
built up over a decade with credit for discovery of ele- Theradioactivedecayisthesimplestformofanuclear
ment103attachingtoworkinbothBerkeleyandDubna. reactionaccordingtoequation[Eq.(6)]:
ThenamelawrenciumafterE.O.Lawrence,theinventor A→B+x+(cid:10)E. (6)
ofthecyclotron,suggestedbyA.Ghiorsoandco-workers
from Berkeley and accepted by IUPAC, was finally rec- Thisisamononuclearreaction.Innuclearscience,how-
ommendedbyIUPACin1997togetherwiththenamesfor ever,binuclearreactionsaregenerallyunderstoodbythe
thetransactinideelementsuptoelement109. term“nuclearreaction.”Theyaredescribedbythegeneral
Table I summarizes the discovery or synthesis of all of equation[Eq.(7)]:
theactinideelements. A+x→B+y+(cid:10)E, (7)
whereAisthetargetnuclide,xistheprojectile,Bisthe
product nuclide, and y is the particle or photon emitted.
II. RADIOACTIVITY AND NUCLEAR Equations(3)–(5)areexamplesforneutron-anddeuteron-
REACTIONS OF ACTINIDES inducednuclearreactions.Withheavyions(heavierthanα
particles)asprojectiles,theheaviestactinideshavebeen
All isotopes of the actinides and actinium are radioac- synthesized. Targets made from heavy actinide nuclides
tive. Table II presents data on several of the most avail- such as 248Cm and 249Bk have been used to synthesize
ableandimportantofthese.Theunstable,radioactiveac- severaltransactinideelementsinheavy-ionreactions.
tinidenucleidecaybyemissionofα particles,electrons, Nuclearfissionofactinidesis,withoutdoubt,themost
orpositrons(β−orβ+decay,respectively).Alternatively important nuclear reaction. Nuclear fission by thermal
to the emission of a positron, the unstable nucleus may neutrons may be described by the general equation
captureanelectronoftheelectronshelloftheatom(sym- [Eq.(8)]:
bol ε). In most cases the radioactive decay leads to an
A+n→B+D+νn+(cid:10)E. (8)
excitedstateofthenewnucleus,whichgivesoffitsexcita-
tionenergyintheformofoneorseveralphotons(γ rays). The fission products B and D have mass numbers in the
In some cases a metastable state results that decays in- rangebetweenabout70and160,thenumberofneutrons
dependently of the way it was formed. Spontaneous fis- emitted is ν≈2–3, and the energy set free by fission is
sion (symbol sf) is another mode of radioactive decay, (cid:10)E ≈200MeV.Thisenergyisrelativelyhigh,because
whichwasdiscoveredin1940byG.N.FlerovandK.A. the binding energy per nucleon is higher for the fission
Petrzhak. products than for the actinide nuclei. In the case of nu-
Thenumerousradionuclidespresentinthoriumandura- clei with even proton and odd neutron numbers, such as
niumoresaremembersofgeneticcorrelatedradioactive 233U,235U,and239Pu,thebindingenergyofanadditional
decay series, which are represented in Fig. 1. In all of neutronisparticularlyhigh,andthebarrieragainstfission
these decay series, only α and β− decay are observed. iseasilysurmounted.Therefore,thesenuclideshavehigh
Withemissionofanα particle(4He),theatomicnumber fissionyieldsforfissionbythermalneutrons.
2
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ActinideElements 215
TABLEI DiscoveryorSynthesisofActinideElements
Most
Atomic Sourceor Isotopefirst stable
number Element Symbol Investigators synthesis discovered isotope Sourceofname
89 Actinium Ac A.Debierne(1899) Uraniumore 227Ac 227Ac Greekwordforray
90 Thorium Th J.J.Berzelius(1828) Thoriumore 232Th 232Th Scandinaviangodof
war,Thor
91 Protactinium Pa K.Fajans,O.Go¨hring Uraniumore 234Pa 234Pa Parentofactinium
(1913) concentrates
92 Uranium U M.H.Klaproth(1789) Pitchblende 238U 238U PlanetUranus
93 Neptunium Np E.M.McMillan, Bombardmentof 239Np 237Np PlanetNeptune
P.Abelson(1940) uraniumwith
neutrons:
238U+1n→
92 0
−β−
239U−−→239Np
92 93
23min
94 Plutonium Pu G.T.Seaborg, Bombardmentof 238Pu 244Pu PlanetPluto
E.M.McMillan, uraniumwith
J.W.Kennedy, deuterons:
A.Wahl(1940) 238U+2H→
92 1
21n+238Np
0 93
−β−
−−−→238Pu
2.1days 94
95 Americium Am G.T.Seaborg, Bombardmentof 241Am 243Am America
R.A.James, plutoniumwith
L.O.Morgan, neutrons:
A.Ghiorso(1944) 239Pu+21n→
94 0
−β−
241Pu −→ 241Am
94 95
96 Curium Cm G.T.Seaborg, Bombardmentof 242Cm 247Cm PierreandMarieCurie
R.A.James, plutoniumwith
A.Ghiorso(1944) heliumions:
239Pu+4He→
94 2
242Cm+1n
96 0
97 Berkelium Bk S.G.Thompson, Bombardmentof 243Bk 247Bk Berkeley,CA
A.Ghiorso, americiumwith
G.T.Seaborg(1949) heliumions:
241Am+4He
95 2
→243Bk+21n
97 0
98 Californium Cf S.G.Thompson, Bombardmentof 245Cf 251Cf California
K.Street,A.Ghiorso, curiumwith
G.T.Seaborg(1950) heliumions:
242Cm+4He
96 2
→245Cf+1n
98 0
99 Einsteinium Es WorkersatBerkeley, Discoveredinthe 253Es 252Es AlbertEinstein
Argonne,and falloutofthefirst
LosAlamos(1952) thermonuclear
explosionasa
resultofuranium
bombardment
withfastneutrons:
238U+151n→
92 0
253U−−7→β−253Es
92 99
Continues
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216 ActinideElements
TABLEI (continued)
Most
Atomic Sourceor Isotopefirst stable
number Element Symbol Investigators synthesis discovered isotope Sourceofname
100 Fermium Fm WorkersatBerkeley, Discoveredinthe 255Fm 257Fm EnricoFermi
Argonne,and falloutofthefirst
LosAlamos(1952) thermonuclear
explosionasaresult
ofuranium
bombardment
withfastneutrons:
238U+171n→
92 0
255U−−8→β−255Fm
92 100
101 Mendelevium Md A.Ghiorso, Bombardmentof 256Md 258Md DimitriMendeleev
B.H.Harvey, einsteiniumwith
G.R.Choppin, heliumions:
S.G.Thompson, 253Es+4He
99 2
G.T.Seaborg(1955) →256Md+1n
101 0
102 Nobelium No E.D.Donets, Bombardmentof 254No 259No AlfredNobel
V.A.Shegolev, americiumwith
V.A.Ermakov(1966) nitrogenions:
243Am+15N
95 7
→254No+41n
102 0
103 Lawrencium Lr Workersatboth Bombardmentsof (258Lr) 262Lr ErnestLawrence
Berkeleyand actinidetargets
Dubna(1961–1971) withheavyions
III. APPLICATIONS OF ACTINIDES cial, and international problems. Technical problems are
relatedtothesafeoperationofnuclearreactors,reprocess-
Thepracticalimportanceoftheactinideelementsderives ing,andwastedisposal,tothepreventionofenvironmen-
mainlyfromtheirnuclearproperties.Theprincipalappli- tal contamination with radioactive and toxic substances,
cation is in the production of nuclear energy. Controlled andtothepreventionofthediversionofplutoniumforan
fission of fissile nuclides in nuclear reactors is used to uncontrolled manufacture of nuclear weapons. All these
provide heat to generate electricity. The fissile nuclides technicalandtechnologicalproblemsaresoluble,butthe
233U,235U,and239Puconstituteanenormous,practically future of nuclear energy depends also on the solution of
inexhaustible,energysource. otherproblemsofacuteglobalconcern.
Severalactinidenuclideshavefoundotherapplications.
Heatsourcesmadefromkilogramamountsof238Puhave
IV. ACTINIDE METALS
been used to drive thermoelectric power units in space
vehicles. In medicine, 238Pu was applied as a long-lived
A. PreparationofActinideMetals
compact power unit to provide energy for cardiac pace-
makersandartificialorgans.241Amhasbeenusedinneu- All of the actinide elements are metals with physical
tronsourcesofvarioussizesonthebasisofthe(α,n)reac- and chemical properties changing along the series from
tiononberyllium.Themonoenergetic59-keVγ radiation those typical of transition elements to those of the lan-
of241Amisusedinamultitudeofdensityandthickness thanides.Severalseparation,purification,andpreparation
determinations and in ionization smoke detectors. 252Cf techniques have been developed considering the differ-
decaysbybothα emissionandspontaneousfission.One entpropertiesoftheactinideelements,theiravailability,
gramof252Cfemits2.4·1012 neutronspersecond.252Cf and application. Powerful reducing agents are necessary
thusprovidesanintenseandcompactneutronsource.Neu- toproducethemetalsfromtheactinidecompounds.Ac-
tronsourcesbasedon252Cfareappliedinnuclearreactor tinidemetalsareproducedbymetallothermicreductionof
start-upoperationsandinneutronactivationanalysis. halides,oxides,orcarbides,followedbytheevaporation
Nuclearenergyandtheapplicationofactinideelements invacuumorthethermaldissociationofiodidestorefine
inotherfieldsmaypromisemankindaprosperousfuture; themetals.
however,whetherthepromisebecomesarealitydepends The metallothermic reduction of halides was the first
onthesolutionofnumeroustechnological,economic,so- method to be successfully applied. Actinium metal can
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ActinideElements 217
TABLEII ImportantIsotopesoftheActinideElements
Atomicnumber Element Isotope Half-life Modeofdecay
89 Actinium 227Ac 21.7years β−(0.986),α(0.014),γ
228Ac 6.15h β−
90 Thorium 232Th 1.405·1010years α,
91 Protactinium 231Pa 32760years α,γ
234Pa 6.70h β−
92 Uranium 235U 7.038·108years α
238U 4.468·109years α
93 Neptunium 237Np 2.144·106years α
94 Plutonium 238Pu 87.7years α
239Pu 2.411·104years α
242Pu 3.733·105years α
244Pu 8.08·107years α(0.999),sf(0.001)
95 Americium 241Am 432.2years α,γ
243Am 7370years α
96 Curium 242Cm 162.8days α
244Cm 18.10years α
248Cm 3.40·105years α(0.916),sf(0.084)
97 Berkelium 247Bk 1380years α(<100%)
249Bk 320days β−(0.99999),α(0.00001)
98 Californium 249Cf 351years α
251Cf 898years α
252Cf 2.645year α(0.969),sf(0.031)
99 Einsteinium 252Es 471.7days α(0.76,ε(0.24)
253Es 20.47days α
254Es 275.7days α
100 Fermium 252Fm 25.39h α(0.99998),sf(0.00002)
255Fm 20.07h α
256Fm 157.6min sf(0.919),α(0.081)
101 Mendelevium 255Md 27min ε(0.92),α(0.08)
256Md 78.1min ε(0.907),α(0.093)
102 Nobelium 259No 58min α(0.75),ε(0.25)
103 Lawrencium 260Lr 3.0min α(0.75),ε(0.25)
be produced by reducing AcF with lithium at 1200◦C. acid treatment dissolves the thorium phosphate present,
3
Smallamountsofactiniumcanbeobtainedfromresidues whilethebasicprocessconvertsthephosphatestoinsol-
ofuraniumprocessing.Gramamountsof227Achasbeen ublehydroxides.Theseparationofthoriumfromtheura-
producedsyntheticallyatMol,Belgium,byneutronirra- niumandrare-earthphosphatesaftertheacidprocesscan
diationof226Ra[Eq.(9)]: becarriedoutbyselectiveprecipitationofthethoriumand
rareearthphosphatesandthenbyusingasolventextrac-
−β−
226Ra + 1n →227Ra + γ −−−→227Ac. (9) tionprocesstoremovethethorium.Whenthealkaliopen-
88 0 88 91
42.2min ingmethodisused,theinsolublehydroxidesaredissolved
Boththoriumanduraniumoccurtoasignificantextentin innitricacidandthethoriumanduranium(VI)speciesare
nature,andindustrialprocesseshavebeendevelopedfor extracted, leaving the lanthanides in the aqueous phase.
theproductionoftheseelements. Thethoriumanduraniumcanthenbeseparatedbyfurther
Thorium is produced commercially from monazite solventextraction.
sands.Aftermining,themonazitesandsareconcentrated Thorium metal can be produced in several ways. In
magneticallyandthentreatedwitheitherhot,concentrated themostcommonprocess,thoriumoxideisreducedwith
sulfuricacidorhot,concentratedsodiumhydroxide.The calcium[Eq.(10)]:
P1:FYKRevisedPages
EncyclopediaofPhysicalScienceandTechnology EN001F-11 May7,2001 12:19
218 ActinideElements
FIGURE1
1000◦C bariumvaporat1300◦C,followedbyincreasingthetem-
ThO2+2Ca −−−→ Th + 2CaO. (10) perature to 1600◦C to produce a bead of protactinium
Ar
metal. Single-crystal protactinium metal is obtained by
Thereactionmassisleachedwithwateranddiluteacid, amodifiedvanArkelprocessstartingfromthecarbide.
leaving thorium metal powder. Very pure thorium metal Morethen150mineralscontaininguraniumareknown.
can be prepared by the van Arkel process involving the Typically,however,uraniumorescontainonlyabout0.1%
thermaldecompositionofThI4. uranium.Inthecommercialproductionofuraniummetal,
Toobtainsignificantquantitiesofprotactinium,asep- theoreiscrushed,concentrated,roasted,andinmostcases
aration procedure was developed for extracting protac- leachedwithsulfuricacidinthepresenceofanoxidizing
tinium from the sludge that was left after the ether agentsuchasmanganesedioxideorchlorateionstocon-
extractionofuraniumattheSpringfieldsrefinery.Thepro- vertalloftheuraniumtouranylsulfatocomplexes.Car-
cessyielded127gofpure231Pafrom60tonsofsludge. bonateleachingisusedtoextracturaniumfromorescon-
ProtactiniummetalcanbeobtainedbyreducingPaF4with tainingmineralssuchascalcite.Therecoveryofuranium