Handbook of Nuclear Chemistry, 2nd Edition

3049 Pages·2010·28.66 MB·English

by  Attila Vértes

Volume 1
Basics of Nuclear Science

1 Nuclear and Radiochemistry:
the First 100 Years
G.Friedlander{1.G.Herrmann2
1BrookhavenNationalLaboratory,Upton,NY,USA
2JohannesGutenberg-Universita¨t,Mainz,Germany
1.1 The Pioneering Years ................................................................ 4
1.2 The Growth Spurt of the 1930s ..................................................... 8
1.2.1 Nuclear Reactions ......................................................................9
1.2.2 Nuclear Properties ................................................................... 10
1.2.3 New Elements ........................................................................ 13
1.2.4 Hot-Atom Chemistry and Tracer Applications ..................................... 14
1.2.5 Geo- and Cosmochronology ......................................................... 15
1.3 World War II .......................................................................16
1.4 The Golden Era ....................................................................18
1.4.1 Nuclear Reactions .................................................................... 19
1.4.2 Nuclear Properties ................................................................... 20
1.4.3 New Elements ........................................................................ 22
1.4.4 Hot-Atom Chemistry and Tracer Applications ..................................... 25
1.4.5 Geo- and Cosmochronology ......................................................... 27
1.5 Current Trends .....................................................................29
{Deceased
AttilaVe´rtes,Sa´ndorNagy,Zolta´nKlencsa´r,Rezso˝G.Lovas&FrankRo¨sch(eds.),HandbookofNuclearChemistry,
DOI10.1007/978-1-4419-0720-2_1,#SpringerScience+BusinessMediaB.V.2011
1
4 NuclearandRadiochemistry:theFirst100Years
Abstract:Thischaptergivesabriefoverviewofthedevelopmentofnuclearandradiochemistry
fromMme.Curie’schemicalisolationofradiumtowardtheendofthetwentiethcentury.The
firstfoursectionsdealwithfairlydistincttimeperiods:(1)thepioneeringyearswhentheonly
radioactive materials available were the naturally occurring ones; (2) the decade of rapid
growth and expansion of both the fundamental science and its applications following the
discoveriesoftheneutronandartificialradioactivity;(3)theWorldWarIIperiodcharacterized
bytheintenseexplorationofnuclearfissionanditsramifications;(4)whatcanbecalledthe
‘‘goldenera’’–the3to4decadesfollowingWorldWarIIwhennuclearsciencewasgenerously
supportedandthereforeflourished.Inthefinalsection,researchtrendspursuedneartheend
ofthecenturyarebrieflytouchedupon.
1.1 The Pioneering Years
The field that became known as radiochemistry, dealing with the chemical manipulation of
radioactive materials and the application of radioactivity to basic and applied chemical
problems, originated very soon after Henri Becquerel had discovered the phenomenon of
radioactivityduringhisstudiesofthefluorescenceofuraniumcompounds(Becquerel1896).
Theterm‘‘radiochemistry’’forthisfieldwasintroducedquiteearly,asindicatedbythefactthat
itappearedinabooktitlein1910(Cameron1910).However,thesametermwasforsometime
alsoappliedtowhatisnowcalled‘‘radiationchemistry,’’thechemicalactionofradioactive(and
other ionizing) radiations. Later, after the concept of the atomic nucleus was introduced in
1911 and especially after the discoveries of nuclear transmutations (1919) and of artificially
produced radioactivity (1934), chemists became involved more broadly in the study of the
production, properties, and reactions of atomic nuclei; in the 1930s, the term ‘‘nuclear
chemistry’’gainedcurrencyforthisbranchofthechemicalsciences,quiteanalogoustoorganic
chemistrybeingconcernedwiththesynthesis,properties,andreactionsoforganicmolecules.
Thecreation,in1937,ofanewchairof‘‘ChimieNucle´aire’’forFre´de´ricJoliotattheColle`gede
Francewasperhapsthefirstofficialrecognitionofthenewbranchofchemistry.Ataboutthe
sametime,OttoHahn’streatiseAppliedRadiochemistry(Hahn1936)clearlyoutlinedthenow
generallyaccepteddefinitionof‘‘radiochemistry.’’
Almost immediately after the discovery of radioactivity, Marie Sklodowska Curie and
PierreCuriebeganmoredetailedstudiesofthenewphenomenon.Guidedbytheirobservation
that some natural uranium ores, such as pitchblende, were more highly radioactive than
correspondedtotheiruraniumcontent(SklodowskaCurie1898),theyfractionatedtheores
chemically,usingtheintensityofradioactivityinthefractionsasevidenceforfurtherradio-
activesubstances.Theresultwasthediscovery,inJune1898,ofanewradioactiveelementin
the bismuth fraction (Curie and Curie, 1898); the Curies named it polonium in honor of
Marie’s homeland. A few months later, in December 1898, they were able to report the
discovery of another radioactive element, this one in the barium fraction separated from
pitchblende (Curie et al. 1898); they named it radium. The subsequent isolation of radium
frombariumwasaccomplishedbyfractionalcrystallizationofbariumchloride,withradium
chloridealwaysbeingenrichedinthecrystallinephase.Itsoonbecamepossibletocharacterize
radiumspectroscopicallybyopticalemissionlines(Demarc¸ay1898)and,thus,toconfirmthe
discovery by an independent identification. By 1902, M. Curie had isolated 120 mg of pure
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NuclearandRadiochemistry:theFirst100Years 5
radium chloride from the residues of about 2 t of pitchblende, a heroic radiochemical
enterprise.Bythen,shewasabletodeterminetheatomicweightofradium.Theresult,225,
providedthefinalproofthatradiumistheheaviestalkalineearthelement(Curie1902).
In1898,M.Curie(SklodowskaCurie1898) (andindependentlyGerhardSchmidt)found
thatnotonlyuranium,butalsothoriumemitsradioactiveradiations,andinthefollowingdecade
numerousotherradioactivesubstances,allofthemultimatelyassignabletoelementsbetween
mercuryanduraniumintheperiodictable,werechemicallyisolatedinvariousfractionsfrom
uraniumandthoriumores.Eventually,allthenewlydiscoveredradioactivesubstancescouldbe
assignedtothreeseparatedecaychains,originatingfromuranium(238U),thorium(232Th)and
from actinium (227Ac) respectively, the last discovered (Debierne 1899; Giesel 1902) in the
lanthanumfractionobtainedfrompitchblende.Eachofthedecayseriesinvolvesanumberof
aandbdecaysandterminatesinoneofthestableleadisotopes(238U!206Pb,232Th!208Pb,
227Ac ! 207Pb). Among the pioneers who contributed to our knowledge of the naturally
occurringradioactivitiesoneshouldfurthermentionBertramBoltwood,JuliusElster,Kasimir
Fajans, Hans Geitel, Georg von Hevesy, Lise Meitner, Stefan Meyer, Fritz Paneth, Egon von
Schweidler,andFrederickSoddy(see,e.g.,MeyerandSchweidler(1916,1927),Jauncey(1946),
Soddy(1975)).
Whenthechemicalpropertiesofmembersofthethreenaturallyoccurringdecayserieswere
investigated,itbecameclearthatsomeoftheradioactivespeciesrepresentedelementsthathad
previouslybeenblankintheperiodictable.Forexample,radium(element88)wassurely the
nexthigherhomologueofbarium;polonium(84)couldbeplacedbelowtelluriumafterithad
turned out that it was identical with the radio-tellurium discovered by Wilhelm Marckwald
(Marckwald 1903), and actinium (89) was positioned below lanthanum. They were later
attributed to 226Ra, with a half-life (T ) of 1,600 years, 210Po (138 days), and 227Ac (21.8
1/2
years). But some of the radioactive species were chemically indistinguishable from existing
elementsorfromeachother.Forexample,theso-calledradiumD(22years,210Pb),amember
oftheuraniumseries,couldnotbechemicallyseparatedfromordinarylead.Similarly,ionium
(8(cid:2)104years,230Th)waschemicallyindistinguishablefromthorium.Furthermore,eachof
the three series contained at least one relatively short-lived member that was chemically
identicalwithlead,oneidenticalwithbismuth,etc.Theseobservationsledtotheconceptof
isotopy,clearlyenunciatedbySoddyin1911andsomewhatlaternamedbyhim(Soddy1911,
1913a).Initially itwasthoughtthatonly radioactiveelementshaveisotopes, i.e.,chemically
identicalspeciesofdifferentatomicweights,butalreadyin1913,JosephJ.Thomsonshowedby
deflectionofpositiveionsinelectricandmagneticfieldsthatordinaryneonconsistedoftwo
isotopesofatomicweights20and22(Thomson1913).Soonitbecameapparentthatisotopyis
ageneralphenomenonamongnaturallyoccurringelements.
Twoimportantdevelopmentsintheearlyhistoryofradioactivitywere(1)therecognition
ofthethreedifferenttypesofradiation,a,b,andgrays,distinguishedbytheirverydifferent
penetrationinmatterand(2)therealizationthatineachofthethreedecayseriesthereexisted
a product that behaved chemically like an inert (also called: rare or noble) gas. Through
experiments involving deflection in magnetic and electric fields, a and b ‘‘rays’’ were soon
identifiedasstreamsofheliumionsandelectrons,respectively,andgrays,undeflectedbysuch
fields,wererecognizedasaformofelectromagneticradiationakintoX-rays.
As early as 1900, Rutherford was able to show that the erratic electrometer readings he
observedwhenmeasuringtheradioactivityofthoriumcompoundswereduetotheemanation
of a radioactive gas into the ionization chamber (Rutherford 1900). The observation that
asampleoftheradioactivegasfadedawaywithinafewminutesaccordingtoacharacteristic
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6 NuclearandRadiochemistry:theFirst100Years
exponentialdecaylawwithawell-reproducibledecayconstantl(wherel=ln2/T )wasoneof
1/2
the fundamental conclusions from these simple experiments. Perhaps even more surprising
was the observation that the gaseous radioactivity could be ‘‘milked’’ repeatedly from the
thorium sample and that the buildup with time in the source occurred with the same time
constantasthedecay process.Furthermore,itwas foundthatevenafter theemanationhad
decayed away, radioactivity persisted as an ‘‘active deposit’’ consisting of nonvolatile decay
products.Thus,thisspecialcaseofanaturalradiochemicalseparationofagaseouscomponent
fromasolidcomponentgavethefirsthintthatradioactivityisaccompaniedbyatransmutation
of elements, and it showed clearly that chemical separations are an excellent tool for the
unravelingofdecaysequences.Radiumandactiniumcompoundswerefoundtoexhibitthe
samephenomenon,i.e.,gaseousemanationsleadingtoactivedeposits,butwithquitedifferent
half-lifepatterns.Detailedstudiesidentifiedtheemanationsasinertgasesofhighmolecular
weight,attributedtoanewelement,theheaviestnoblegas,radon(element86).
ThevariousdevelopmentsjustmentionedledRutherfordandSoddytoformulateatheory
ofradioactivetransformationpublishedinaremarkableseriesofpapersthathasremainedvalid
initsessentialstothisday(RutherfordandSoddy1902,1903).Theypositedthatradioactive
decayinvolvesthespontaneoustransformationofatomsofoneelementintothoseofanother,
accompaniedbytheemissionofparticles.Withthishypothesis,theythusintroducedtherather
revolutionarynotionthatatoms,previouslythoughttobeimmutable‘‘elementaryparticles,’’
areinfactcompositestructurescapableofsubatomicchange.Thiswasaparticularlyremark-
ableproposalwhenoneconsidersthatitprecededbysome8yearstheconceptoftheatomic
nucleus.
Oncethenatureofaandbparticleshadbeenestablishedandradioactivedecayhadbeen
recognized as involving subatomic change, it became possible to formulate rules for the
placementofradioelementsintheperiodictable.Theseso-calleddisplacementlaws,enunci-
atedin1913(Fajans1913;Soddy1913b),statethattheproductofadecayistheelementtwo
columnstotheleftoftheparentelement,whereasbdecayinvolvesaone-columnshifttothe
right.Onthebasisoftheserulesitwasnowpossibletoplacealltheknown,naturallyoccurring
radioactivespeciesofthethreedecayseriesintotheperiodictablewiththeinclusion,asalready
mentioned,ofnumerousisotopicspecies.Eachoftheseriesalsocontainsexamplesofso-called
branchingdecays,i.e.,instancesofagivenspeciesdecayingbybothaandbdecay.Withthe
discoveryofthelong-lived231Pa(3.3(cid:2)104years)astheparentof227Ac(HahnandMeitner
1918),themajorroutesofthethreedecayserieswereestablished.Theobservation(Hahn1922)
thatthepositionof234Paintheuraniumdecayseriesissharedbytwospecieswithdifferent
half-lives(1.17minand6.7h)remainedacuriosityformanyyears,untilitwasunderstoodas
the discovery of nuclear isomerism, representing the ground and a metastable, excited state.
Furtherworkonthenaturalserieswasdevotedtoraredecaybranches.
The first realization that radioactivity was not confined to the heaviest elements came
withtheobservationin1906ofweakbradioactivityinpotassiumandrubidium(Campbell
andWood1906).Asmeasurementtechniquesbecamemoreandmoresensitive,weakradio-
activitywasdiscoveredinseveralothernaturallyoccurringelements(e.g.,In,Nd,Sm,Gd,Lu,
Hf,andRe).
Theidentificationofradioactivedecayasasubatomicprocessled,ofcourse,totheoriesof
atomicstructure.Aftervariousmodelshadbeensuggested–noneofthemtotallysatisfactory–
thebigbreakthroughcamewithRutherford’sclassic1911paper(Rutherford1911)inwhichhe
proposed,onthebasisofcareful,quantitativeexperimentsonthescatteringofaparticlesfrom
thinmetallicfoils,thatmostofthemassofanatommustbeconcentratedinapositivelycharged
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NuclearandRadiochemistry:theFirst100Years 7
nucleus,extremelysmallwhencomparedtothesizeoftheatom;thepositivenuclearchargewas
thought to be balanced by an equal negative charge carried by electrons surrounding the
nucleus.BasedonthisconceptandonCoulomb’slaw,Rutherfordwasabletoderiveaformula
thatgivesdetailedpredictionsofa-particlescatteringanditsdependenceonnuclearcharge.
Experimental verification of these predictions led to awidespread acceptanceof the nuclear
modelandtotherealizationthatanelement’satomicnumber,hithertomerelyindicatingthe
element’splacementintheperiodictable,isinfactitsnuclearcharge(inunitsoftheelectronic
charge e). Once Rutherford’s nuclear model of the atomwas accepted, elucidation of atomic
structuremaderapidstrides,importantmilestonesbeingNielsBohr’stheoryofelectronorbits
(Bohr1913)andthequantumrevolutionofthemid-1920s.
Withtime,thepioneersofradiochemistrydevelopedagreatvarietyofchemicalseparation
techniquesfortheunravelingofthenaturaldecayseries,includingco-crystallization,adsorp-
tion,volatilization,andelectrochemicaldeposition.Thequantitiesoftheradioisotopeshan-
dled–asestimatedfromthedecayrate–wereoftensmallerbyordersofmagnitudethancould
bedetectedbyanyothermethod.Hence,studiesofthechemistryofextremelylow,‘‘impon-
derable’’quantitiesbecameamajorresearchfieldofradiochemistsduringthefirstdecadesof
thetwentiethcentury(see,e.g.,Hahn1936).Atsuchalevel,deviationsfromthebehaviorof
macroscopicamountsarenotunexpected.Forexample,thevaporpressureandtheevapora-
tion ratearenormallygoverned by thecohesiveforcesbetween themolecules ofthespecies
itself.Incaseofamonomolecularlayercoveringabacking,theydepend,however,largelyon
theinteractionbetweenspeciesandbackingmaterial.Ontheotherhand,whenradiochemists
want to ensure ‘‘normal’’ chemical behavior of a trace quantity of a radionuclide, they add
a macroscopic quantity of a nonradioactive carrier, usually of the same element in the same
chemicalforminwhichthetraceelementisthoughttobepresent.
Path-breakingworkthateventuallyspawnedwholenewfieldswasdoneinthoseearlyyears.
Forexample,thepotentialofradioactivedecaytoserveasaclockforgeologicalprocesseswas
realizedbyRutherfordasearlyas1906(Rutherford1906)whenheproposedtheamountof
heliuminuranium ores asa measureof thetime sincecrystallizationoftheore.ThisHe/U
methodprovidedthefirstproofthatgeologicalprocessesmusthaveoccurredovertimesofthe
orderof108to109years,ordersofmagnitudelongerthanindicatedbypreviousmethods.This
revolutionaryconclusionwasconfirmedin1907whenleadwasrecognizedasthefinal,stable
productofuraniumdecay(Boltwood1907),whichmeantthatthePb/Uratiocouldbeusedas
achronometer.FurtherrefinementofthisPb/Umethodbecamepossiblewhenpreciseatomic
weightdeterminationsshowed(RichardsandLembert1914;Ho¨nigschmidandHorovitz1914)
theleadinsomeuraniumoreshadanatomicweightcloseto206ratherthantheusual207.2,
thusidentifyingitasradiogenic.
Alsooffar-reachingconsequenceswastheidea(HevesyandPaneth1913)touseradioiso-
topesasindicatorsortracersinchemical,physical,andbiologicalstudiesbecauseradioactive
and stable isotopes are chemically indistinguishable. Hevesy and Paneth determined the
solubility of sparingly soluble lead salts by labeling the samples with radioactive lead and
measuringtheradioactivityinthesolutionafterequilibration.Theresultcanbeobtainedby
othertechniquestoo,butnotinsuchasimplewayaswithradioactiveindicators.Thisholdsfor
mostindicatorapplications.
However,itwasrealizedearlyonthatthereisacategoryofproblemsthatcanbeattacked
only with radioactive (or stable isotope) indicators: the behavior of an element in some
chemical form in the presence of the same element in a different chemical form. The first
examplewasHevesy’sworkontheexchangeofleadbetweensolidleadmetalanditsionsin
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8 NuclearandRadiochemistry:theFirst100Years
solution(Hevesy1915),inwhichthedynamicalexchangeprocesspostulatedasafundamental
concept of chemical kinetics was directly verified. Even the fate of a species in an identical
environmentcanbefollowed,asheshowedfortheself-diffusionofleadinmolten(1920)and
solid (1929) lead metal. The most seminal development was the extension of the tracer
techniquetolifesciencesbyHevesyandhiscoworkers.In1923,theystudiedtheuptakeand
transportofleadinplants(horsebeans)includingtheproofthattransportandfixationoccur
inionicform(Hevesy1923);ayearlatercamethefirsttracerstudyinanimals,areportonthe
circulationofbismuthinrabbits(Christiansenetal.1924).Asearlyas1927,anapplicationto
human subjects was reported (Blumgart and Weiss1927), the studyof blood circulation by
injection of 222Rn decay products. This work represents also a generalization of the tracer
conceptbeyondtheoriginalideaofisotopictracers.
Thoughthepotentialofthetracertechniquewasclearlydemonstratedinsuchstudies,the
inputtochemistryandother fieldsremainedsomewhatlimitedaslongasradioactivitywas
confined to the heaviest elements occurring in the natural decay series. The epoch-making
eventthatledtoavastexpansionofnuclearandradiochemistrywasIre`neCurie’sandFre´de´ric
Joliot’sdiscoveryofartificiallyproducedradioactivity(CurieandJoliot1934).Nuclear trans-
mutation by a-particle bombardment – specifically the nuclear reaction 14N(a,p)17O – had
been discovered by Rutherford in 1919 when he observed energetic protons during the
bombardment of nitrogen with a particles from a natural source (Rutherford 1919). The
newphenomenonofinducedradioactivityappeared,e.g.,inbombardmentsofaluminumwith
a particles as a nuclide decaying with 3 min half-life that could be chemically identified
with phosphorus. The process involved was immediately understood as a nuclear reaction,
27Al(a,n)30P,thistimeleadingtoanunstableratherthanastableproductnucleus.
1.2 The Growth Spurt of the 1930s
Thediscoveryofartificiallyproducedradioactivitycameontheheelsofseveralothercrucial
events:thediscoveriesoftheneutron(Chadwick1932)andofdeuterium,theheavyisotopeof
hydrogen (Urey et al. 1932), and the invention of devices – electrostatic generator (Van de
Graaffetal.1933),cyclotron(LawrenceandLivingston1931),voltagemultiplier(Cockcroft
and Walton 1930, 1932) – capable of accelerating charged particles to energies needed
fornucleartransformations.Theinventionofaveryversatile,electroniccounterforradioac-
tivity (Geiger and Mu¨ller 1928) was another important step. Neutron capture in nuclei was
discoveredbyEnricoFermiandcoworkers(Fermietal.1934)asanalternativeandefficient
methodfortheproductionofradioisotopes,suchas128I(T =25min)fromthe127I(n,g)
1/2
reaction. The activations could be carried out with small neutron sources consisting of
berylliumpowdermixedwith226Raasa-particlesource(i.e.,usingthe9Be(a,n)12Creaction)
soonavailableinmanyradiochemicallaboratories,andtheyieldscouldbeincreasedsubstan-
tiallywithneutronssloweddowninhydrogen-containingmaterial(FermiandRasetti1935;
Pontecorvo1935).
Alsoin1934,LeoSzilardandT.A.Chalmersobservedthatneutroncaptureisaccompanied
by chemical effects (Szilard and Chalmers 1934); when ethyl iodide was irradiated with
neutrons,abouthalfoftheproduced128Iwasnotorganicallybound,butcouldbeextracted
with water in the form of iodide. The recoil energy transferred to the iodine atom by the
emittedgrayexceedsbymorethanoneorderofmagnitudetheenergyofthecarbon-iodine
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NuclearandRadiochemistry:theFirst100Years 9
chemicalbondandisthussufficienttobreakthebond.Thisworkopenedthenewresearchfield
ofchemicaleffectsofnucleartransformations,oftenreferredtoashot-atomchemistry.
Thesedevelopments,allwithinatimespanof5years,ledtorapidburgeoningofnuclear
physicsandchemistryinthe1930s.Newnuclearspecies–nuclidesastheycametobecalled–
werediscoveredeveryweek,withhalf-livesrangingfromfractions ofasecondtothousands
ofyears.Amongthenewlydiscoverednuclidesweremanythatlatergainedgreatimportance
astracersinmedicalpracticeandinindustry,including131I,60Co,32P,and14C.Bytheoutbreak
of World War II in 1939, several hundred artificially produced radioactive nuclides were
known (see, e.g., Seaborg 1940) and at the end of the century the number was somewhere
around3,000.
One might ask why chemists, along with physicists, got into the game of discovering,
identifying, and studying radioactive nuclei and their properties as well as investigating the
mechanismsofthenuclearreactionsproducingthem.Tosomeextentthiscameaboutbecause
irradiationofagiventargetelementwithagivenprojectileoftenledtoavarietyofradioactive
productsthathadtobeseparatedandidentifiedchemically.Buttherewasalsotheintrinsic
interestofthesubjectmatterandtheobviousparallelsbetweenchemicalandnuclearreactions,
aswellasbetweenatomicandnuclearstructures.
1.2.1 NuclearReactions
By the late 1930s, the systematic studyof nuclear reactions induced byvarious projectiles –
protons,neutrons,deuterons,andaparticles–attherangeofparticleenergiesthenavailable
(uptoabout40MeV)ledtoanunderstandingoftheprevalentreactionmechanismintermsof
NielsBohr’scompound-nucleusmodel(Bohr1936).Inthismodel,theincidentparticleamal-
gamateswiththetargetnucleustoformaso-calledcompoundnucleus,inwhichtheparticle’s
kinetic and potential energy is shared by all the nucleons. The compound nucleus may be
thoughtofasthenuclearanalogueoftheexcited,quasi-stationarytransitionstateinchemical
reactions. After manycollisions among the nucleons, taking typically 10(cid:3)14–10(cid:3)19 s (a long
time in nuclear dimensions), enough excitation energy may be concentrated by statistical
fluctuationsononenucleon(orclusterofnucleonssuchasanaparticle)toallowittoescape
from its confinement in the potential well of the nucleus. This slow second step is called
‘‘evaporation,’’ in analogy to the escape of molecules from a drop of hot liquid, a concept
introducedintonuclearphysicsinthemid-1930s(Frenkel1936;BohrandKalckar1937)and
soonwidelyaccepted.Anessentialpointofthecompound-nucleusmodelistheindependence
oftheevaporationstepfromthemodeofformationofthecompoundnucleus,andthiswas
confirmedinthe1950sand1960sbyradiochemicalstudiesoftheproductionofradioactive
nuclidesviathesamecompoundnucleusformedindifferentways.
Althoughthecompound-nucleusmodelaccountswellforalargebodyofnuclearreactions,
itbecameclearearlyonthatthereareexceptions.Forexample,insomedeuteronirradiationsit
was found that protons are emitted preferentially in the forward direction, whereas the
compound-nucleus picture (evaporation) would predict an essentially isotropic emission.
These (d,p) reactions are interpreted as ‘‘stripping’’reactions, i.e., the deuteron’s neutron is
strippedoffbythetargetnucleusandtheprotonjustcontinuesonitspath(Oppenheimerand
Phillips1935).Thisisanexampleofso-calleddirectreactions,whichcanoccurwiththetransfer
oflargerpiecesalso,e.g.,transferofanaparticlefroma12Cprojectiletothetargetnucleus.