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原文：Technetium:behaviourduringreprocessingofspentnuclearfuelandinenvironmentalobjectsAbstract：Thereviewsurveysmainchemicalpropertiesoftechne-tium,methodsofitsisolationanddeterminationanditsbehaviorduringreprocessingofspentnuclearfuelandinenvironmentalobjects.Methodsforextractionandisolationoftechnetiumasahazardouslong-livedradionuclidearedescribed.Prospectsofusingtechnetiuminindustrialprocessesandinmedicineareconsidered.Thebibliographyincludes276references.I.IntroductionTechnetiumisaGroupVIIelement,whichwasfirstpreparedbynuclearsynthesisinthemid-twentiethcentury.Thecharacteristicfeatureoftechnetiumisthatallitsisotopeswithmassnumbersfrom90to110areradioactive.Technetiumisanartificialelementanddoesnotoccurinnature.However,morethan60tonnesofTchaveaccumulatedintheworldbecausespentnuclearfuel(SNF)hasahighTccontent(0.6gperkilogramof235Uinthecaseof50%burn-up).1Largeamountsoffissionproducts(FP),includingTc,werereleasedintotheenvironmentfromnuclearweaponproductionandnuclearpowerengineering.Sincethe99Tcisotopehasalonghalf-life,itisaveryhazardousradioactiveelement.Besides,technetiumshowsahighmigrationabilityandsomeofitscompoundsarevolatile.Themainchemicalandphysicochemicalpropertiesoftechnetiumarewellknownandweredescribedinmonographsandreviewsaswellasinthehandbookpublishedin1999.10However,manynewstudiespublishedinrecentyearsrequiregeneralisation.Besides,progressinnuclearpowerengineeringhasgeneratedaneedforadditionalstudiesofthebehaviourofTcduringreprocessingofspentnuclearfuelandinenvironmentalobjects.ThelackofthenecessaryinformationonimportantradiochemicalpropertiesandbehaviouroftechnetiuminnaturalobjectshasalreadyledtocontaminationoftheenvironmentbyalargeamountofTc.ThepresentreviewsurveysthemainpropertiesoftechnetiumresponsibleforitsbehaviourduringreprocessingofSNFandinenvironmentalobjects.Thesedatamaybeofuseforimprovementsinpresent-daytechnologiesforreprocessingofSNFfromtheviewpointofoptimisationandcompleteextractionofTcaswellasforthepredictionofitsbehaviourinnaturalobjects.II.Discovery,methodsofpreparationandmainpropertiesoftechnetiumDIMendeleevwasthefirsttosupposethatachemicalelementwiththeatomicmassof99shouldbepresentbetweenmanganeseandrheniuminthePeriodicTable(andgaveitthenameekamanganese).However,thediscoveryofthiselementinmanganese-containingoresandmineralsappearedtobeadifficultproblem.Allattemptstoisolatethenewelementwiththeatomicnumber43failed.TheRussianchemistShchukarevandGermanphysicistMattauchformulatedthe‘prohibitionrule’statingthattheisobarsoftwoadjacentelementsinthePeriodicTablecannotbestable,i.e.,oneoftheseelementsisnecessarilyradioactive.Thisledtotheconclusionthattheelementwiththeatomicnumber43couldnothavestableisotopesand,consequently,couldnotoccurinnature.1.PreparationandnuclearpropertiesoftechnetiumisotopesIn1937,PerrierandSegrecarriedoutthefirstexperimentsonisolationoftheelementwiththeatomicnumber43fromamolybdenumtargetbombardedwithdeuteronsonacyclotronaccordingtothereactionAMo42(d,n)A+1Tc43.Thenewelementwasnamedtechnetium(fortheGreekword‘tewnZos’,whichmeansartificial).Lateron,anotherprocedurewasdevelopedforthepreparationofTcbyirradiationofmolybdenum-containingsamplesinslowneutronflux98Mo(n,γ)99Moβ-→99mTcγ→99Tc.KilogrammeamountsofeitherspectrallypureMoO3ormolybdenummetalareusedasatarget.Thetargetisirradiatedinareactorforoneyearandkeptuntiltheparent99Moisotopecompletelydecays.Irradiationof1kgofmolybdenumwithafluxof8×1013neutronscm-2s-1makesitpossibletoaccumulateupto60mgofTc.Isolationoftechnetiummustbecarriedoutin‘hot’chambersoperatingunderremotecontrolatahotlaboratory,whereastheyieldsremainlow.Inthisconnection,isolationoftechnetiuminthecourseofSNFreprocessingispresentlyamoreconvenientprocedure,becausetechnetiumisafissionproductaccumulateduponirradiationofnuclearfuelinareactor.TheaccumulationofTcdependsonthenatureofthefissionablenuclideandthedepthofburn-upandreaches*1kgpertonneoffuelinfast-neutronreactors.18Theyieldof99Tcduringfissionof235Uor239Puisabout6.1%.OtherTcisotopeswiththemassnumbersfrom99to110inclusivewerealsofoundamongfissionproductsofuranium.Theseisotopesareproducedthroughβ--decayorneutroncapture.However,nuclearreactorsproducetheseisotopesininsignificantyields.Oftechnetiumisotopes,thelong-lived99Tcisotope(t1/2=2.14×105years)isofparticularimportance.Thisisotopeservesasab-rayemitterwiththeenergyEβmax=292keV,anditsdecayisnotaccompaniedbyγ-radiation.The99mTcisotope(t1/2=6.6h)iswidelyusedinmedicine.Thisradionuclideismostcommonlyisolatedwiththeuseofchromatographic,extractionorsublimationgeneratorsbasedon99Mo.GeneratorsbasedonsublimationseparationofTcoutperformgeneratorsofothertypesinmanyrespects.TheirconstructionassumesheatingofMoO3to850℃inaflowofO2.Theyieldof99mTcobtainedbysublimationofvolatiletechnetiumoxideanditscondensationinacooledreceiverfollowedbydissolutionofthecondensatereaches1Ciml-1.Thetypeof99mTcdecayistheisomerictransitionofthenucleusfromametastablestatetoalower-energylevel.Instudiesof99mTc,itwasdemonstratedthatthechemicalstateoftheelementhasonlyaslighteffectontherateofdecayofanunst