海洋中的放射化學(xué)

海洋中的鈾系放射化學(xué)

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主講：蔡平河電話：2880179；e-mail:Caiph@高級海洋化學(xué)

（2016-4-28）Thethreedecayseriesnowadaysrecognized1.ThebirthofUranium-SeriesScience

ThediscoveryofRadiationin1896byHenriBeckquerelwhenheinvestigatedtheraysemittedbyphosphorescenturaniumsalt(Becquerel1896a,1896b)HenriBeckquerel(1852-1908)TheinvestigationsoftheradioactivityofuraniumandthoriumledtothediscoveryofRadiumandPoloniumbytheCuries(Curie1898;CurieandCurie1898;Curieetal.,1898)MarieCurie(1867-1934)In1899,ErnestRutherfordidentifiedtwodifferentformsofradiation—alphaandbetarays(Rutherford1899).

ErnestRutherford(1871-1937)TheActinium(Ac)wassoonunearthed(Debierne1900)afterthediscoveryofRaandPo.

TheintroductionofthedecayequationfromThemanation:dN/dt=-lNandtheconceptofhalf-lives(Rutherford1900a);半衰期的概念The“excitedactivity”byThemanation—212Pb(Rutherford1900b):Thefirstdescriptionofsecularequilibrium:

“Thenormalofconstantradioactivitypossessedbythoriumisanequilibriumvalue,wheretherateofincreaseofradioactivityduetotheproductionoffreshactivematerialisbalancedbytherateofdecayofradioactivityofthatalreadyformed”

RutherfordandSoddy(1902)

Thefirstpublishedsetof“U-series”in1903(Rutherford1903):

Radioactivityreleasedlargequantitiesofheat(CurieandLaborde1903)AlphadecayreleaseHe(RamsayandSoddy1903)Thebuild-upofHewasputtousetodategeologicalmaterialThedatingoftheEarthusingU-PbmethodproposedbyBoltwood.Thediscoveryof230Th(ionium)

byBoldwood(1907)Introductionoftheterm“isotope”(Soddy,1910;1913)234Pa(brevium)wasdiscoveredin1913(FajanandGohring)DisplacementruleofatomicdecaywasdeducedindependentlybyFajansandSoddy(Soddy1913;Fajans1913).Thethreedecayseriespublishedin1913.Thethreedecayseriesnowadaysrecognized

核衰變類型

—alpha衰變核衰變類型

—Beta衰變核衰變類型

—Beta衰變核衰變類型

—Beta衰變原子核的衰變規(guī)律原子核的衰變規(guī)律N=-Ntor:dN=-NdtlnN=-t+Cift=0,N=N0andC=lnN0,then:N=N0e-t原子核的衰變規(guī)律

—衰變常數(shù)、半衰期和平均壽命

衰變常數(shù)：-dN/dt=N

=（-dN/dt）/N

半衰期：

Ift=T1/2,then:N=1/2N0=N0e-T1/2

T1/2=0.693/

平均壽命：=1/or=1.44T1/2

原子核的衰變規(guī)律

—放射性活度及其單位放射性活度：A=-dN/dt=N=N0e-t

或：A=A0e-t單位：1Ci=3.71010dps1Bq=1dps1Bq=60dpm放射性活度:

238Uand234Thactivitiesindeep-seawater：

238U=234Th=2.45dpm/LN(238U)=8.31E+15;N(234Th)=1.23E+5C(238U)=3.28E-6g/L;C(234Th)=4.77E-17g/L;原子核的衰變規(guī)律

—兩次連續(xù)衰變90Sr

-

90Y

-90Zr(Stable)95Zr

-

95Nb

-95Mo(Stable)99Mo

-

99mTc

99Tc(Stable)113Sn

-

113mIn

113In(Stable)ABC(穩(wěn)定)

半衰期T1/2(1)T1/2(2)

衰變常數(shù)1

20t=0N1,000t=tN1N2N3

對于A:N1=N1,0e-1t;-dN1/dt=1N1

對于B:dN2/dt=1N1-2N2dN2/dt=1N1,0e-1t-2N2Solution:N2=[1/(2-1)]N1,0(e-1t-e-2t)原子核的衰變規(guī)律

—兩次連續(xù)衰變原子核的衰變規(guī)律

—兩次連續(xù)衰變：暫時平衡N2=[1/(2-1)]N1,0

e-1t[1-e-(2-1)t]IfT1/2(1)>T1/2(2)i.e.2>1,andt足夠長時,e-(2-1)t<<1,then:N2=[1/(2-1)]N1,0

e-1t=[1/(2-1)]N1or:N2/N1=1/(2-1)=Cor:A2/A1=2/(2-1)原子核的衰變規(guī)律

—兩次連續(xù)衰變：暫時平衡原子核的衰變規(guī)律

—兩次連續(xù)衰變：長期平衡90Sr

-(28.8y)

90Y

-(

64.1h)90Zr(Stable)137Cs

-(30.17y)

137mBa

(

2.551min)137Ba(Stable)IfT1/2(1)>>T1/2(2),2>>1,2-12then:N2=(1/2)N1,0

e-1t(1-e-2t)Ift>7T1/2(2),e-2t0then:N2=(1/2)N1,0

e-1t=(1/2)N1or:2N2=1N1原子核的衰變規(guī)律

—兩次連續(xù)衰變：不成平衡129Te

-(69min)

129I

-(

1.6107y)129Xe(Stable)103Tc

-(50s)

103Ru

-(

39.4y)103Rh(Stable)N2=[1/(1-2)]N1,0

e-2t[1-e-(1-2)t]IfT1/2(1)<T1/2(2)or1>2,andt>7T1/2(1),thene-(1-2)t0N2=[1/(1-2)]N1,0

e-2t原子核的衰變規(guī)律

—多次連續(xù)衰變：四個放射系鈾系（4n+2）238U234Th234mPa234U230Th226Ra222Rn218Po214Pb214Bi214Po210Pb210Bi210Po206Pb原子核的衰變規(guī)律

—多次連續(xù)衰變：四個放射系1.2錒系（4n+3）235U231Th231Pa227Ac227Th223Ra219Rn215Po211Pb211Bi211Po207Pb

原子核的衰變規(guī)律

—多次連續(xù)衰變：四個放射系1.3釷系（4n）

232Th228Ra228Ac228Th224Ra220Rn216Po212Pb212Bi212Po208Pb

原子核的衰變規(guī)律

—多次連續(xù)衰變：四個放射系1.4镎系（4n+1）

241Pu241Am237Np233Pa233U229Th225Ra225Ac221Fr217At213Bi213Po209Pb209Bi

原子核的衰變規(guī)律

—多次連續(xù)衰變規(guī)律

(1)(2)(3)…(n)衰變常數(shù)

1

2

3

nt=0時的原子數(shù)

N1,0000t時刻的原子數(shù)N1N2N3NndN1/dt=-1N1dN2/dt=1N1-2N2dN3/dt=2N2-3N3…dNn/dt=n-1Nn-1-nNnSolution:N1=N1,0e-1t,N2=[1/(2-1)]

N1,0(e-1t-e-2t)代入上式得：N3=12N1,0[e-1t/[(2-1)(3-1)]+e-2t/[(1-2)(3-2)]+e-3t/[(1-3)(2-3)]…Nn=12…n-1N1,0(C1e-1t+C2e-2t+…+Cne-nt)WhereC1=1/[(2-1)(3-1)…(n-1)]C2=1/[(1-2)(3-2)…(n-2)]Cn=1/[(1-n)(2-n)…(n-1-n)]原子核的衰變規(guī)律

—多次連續(xù)衰變規(guī)律原子核的衰變規(guī)律

—多次連續(xù)衰變規(guī)律鈾系不平衡在海洋學(xué)中的應(yīng)用—虧損（deficit)與過剩(excess)鈾系不平衡在海洋學(xué)中的應(yīng)用—虧損（deficit)與過剩(excess)鈾系不平衡在海洋學(xué)中的應(yīng)用—虧損（deficit)與過剩(excess)鈾系不平衡在海洋學(xué)中的應(yīng)用—（1）海洋沉積物表層沉積過程的研究：a.沉積速率鈾系不平衡法在海洋學(xué)中的應(yīng)用—（1）海洋沉積物表層沉積過程的研究：a.沉積速率鈾系不平衡法在海洋學(xué)中的應(yīng)用—（1）海洋沉積物表層沉積過程的研究：a.沉積速率Thegeneraldiageneticequations:鈾系不平衡在海洋學(xué)中的應(yīng)用—（1）海洋沉積物表層沉積過程的研究：a.沉積速率鈾系不平衡在海洋學(xué)中的應(yīng)用—（1）海洋沉積物表層沉積過程的研究：a.沉積速率:平流與擴散The1Dadvection-diffusionbalance:Ithasthesolution:

Hereccaneitherbepot.temp.,salinityorDICetc,andc0,c1andHarethreeunknowns,tobedeterminedthroughfittingtheobservedprofiles.(SeeWalterMunk’s1966DSRpaperforitsapplication.)鈾系不平衡在海洋學(xué)中的應(yīng)用—（1）海洋沉積物表層沉積過程的研究：a.沉積速率鈾系不平衡在海洋學(xué)中的應(yīng)用—（1）海洋沉積物表層沉積過程的研究：a.沉積速率鈾系不平衡法在海洋學(xué)中的應(yīng)用—（1）海洋沉積物表層沉積過程的研究：a.沉積速率鈾系不平衡在海洋學(xué)中的應(yīng)用—（1）海洋沉積物表層沉積過程的研究：a.沉積速率鈾系不平衡法在海洋學(xué)中的應(yīng)用—（1）海洋沉積物表層沉積過程的研究：a.沉積速率:230Th;14C鈾系不平衡法在海洋學(xué)中的應(yīng)用—（1）海洋沉積物表層沉積過程的研究：b.混合速率放射性同位素：234Th(24.1d),7Be(53.4d)化學(xué)行為：234Th:particlereactive;7Be:modestparticlereactivity.來源：234Th:decayfrom238U;7Be:Naturallyp