海洋中的放射化學(xué)

1、主講：蔡平河 電話：2880179；e-mail: C 高級海洋化學(xué) （2016-4-28） The three decay series nowadays recognized The discovery of Radiation in 1896 by Henri Beckquerel when he investigated the rays emitted by phosphorescent uranium salt (Becquerel 1896a, 1896b) Henri Beckquerel (1852-1908) The investigations of the radioa

2、ctivity of uranium and thorium led to the discovery of Radium and Polonium by the Curies (Curie 1898; Curie and Curie 1898; Curie et al., 1898) Marie Curie (1867-1934) In 1899, Ernest Rutherford identified two different forms of radiation alpha and beta rays (Rutherford 1899). Ernest Rutherford (187

3、1-1937) The Actinium (Ac) was soon unearthed (Debierne 1900) after the discovery of Ra and Po. The introduction of the decay equation from Th emanation: dN/dt=-l lN and the concept of half-lives (Rutherford 1900a); 半衰期的概念半衰期的概念 The “excited activity” by Th emanation 212Pb (Rutherford 1900b): The fir

4、st description of secular equilibrium: “The normal of constant radioactivity possessed by thorium is an equilibrium value, where the rate of increase of radioactivity due to the production of fresh active material is balanced by the rate of decay of radioactivity of that already formed ” Rutherford

5、and Soddy (1902) The first published set of “U-series” in 1903 (Rutherford 1903): Radioactivity released large quantities of heat (Curie and Laborde 1903) Alpha decay release He (Ramsay and Soddy 1903) The build-up of He was put to use to date geological material The dating of the Earth using U-Pb m

6、ethod proposed by Boltwood. The discovery of 230Th (ionium) by Boldwood (1907) Introduction of the term “isotope” (Soddy, 1910; 1913) 234Pa (brevium) was discovered in 1913 (Fajan andGohring) Displacement rule of atomic decay was deduced independently by Fajans and Soddy (Soddy 1913; Fajans 1913). T

7、he three decay series published in 1913. The three decay series nowadays recognized 核衰變類型核衰變類型 alpha alpha衰變衰變 HeYX HeRnRa A Z A Z 4 2 4 2 4 2 222 86 226 88 核衰變類型核衰變類型 Beta Beta衰變衰變 YX PoBi A Z A Z1 210 84 210 83 ：衰變 YX BC A Z A Z1 1111 衰變： 核衰變類型核衰變類型 Beta Beta衰變衰變 YX LiBe A Z ECA Z EC 1 77 電子俘獲： 核衰

8、變類型核衰變類型 Beta Beta衰變衰變 原子核的衰變規(guī)律原子核的衰變規(guī)律 原子核的衰變規(guī)律原子核的衰變規(guī)律 N=-l lN t or: dN=-l lNdt lnN=-l lt+C if t=0, N=N0 and C=ln N0, then: N= N0e-l lt 原子核的衰變規(guī)律原子核的衰變規(guī)律 衰變常數(shù)、半衰期和平均壽命衰變常數(shù)、半衰期和平均壽命 衰變常數(shù)衰變常數(shù)：-dN/dt=lN l=（-dN/dt）/N 半衰期半衰期： If t=T1/2, then: N=1/2N0= N0e-lT1/2 T1/2=0.693/l 平均壽命平均壽命： =1/l l or =1.44 T1/

9、2 原子核的衰變規(guī)律原子核的衰變規(guī)律 放射性活度及其單位放射性活度及其單位 放射性活度放射性活度：A=-dN/dt=l lN=l l N0 e-l lt 或：或：A=A0 e-l lt 單位：單位：1Ci=3.7 1010dps 1Bq=1dps 1Bq=60dpm 放射性活度放射性活度: 238U and 234Th activities in deep-sea water： 238U=234Th=2.45 dpm/L N(238U)=8.31E+15; N(234Th)=1.23E+5 C(238U)=3.28E-6 g/L; C(234Th)=4.77E-17 g/L; 原子核的衰變規(guī)律

10、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) A B C (穩(wěn)定穩(wěn)定) 半衰期半衰期 T1/2(1) T1/2(2) 衰變常數(shù)衰變常數(shù) l l1 l l2 0 t=0 N1,0 0 0 t=t N1 N2 N3 對于對于A: N1=N1,0 e-l l1t ; -dN1/dt=l l1 N1 對于對于B: dN2/dt=l l1 N1-l l2 N2 dN2/dt=l l1 N1,0 e-l l

11、1t-l l2 N2 Solution: N2=l l1/(l l2-l l1) N1,0(e-l l1t- e-l l2t) 兩次連續(xù)衰變兩次連續(xù)衰變 原子核的衰變規(guī)律原子核的衰變規(guī)律 兩次連續(xù)衰變：暫時平衡兩次連續(xù)衰變：暫時平衡 N2=l l1/(l l2-l l1) N1,0 e-l l1t 1- e-(l l2-l l1)t If T1/2(1) T1/2(2) i.e. l l2l l1, and t足夠長時足夠長時, e-(l l2- l l1)tT1/2(2), l l2l l1, l l2-l l1ll2 then: N2=(l l1/l l2) N1,0 e-l l1t(1-

12、 e-l l2t) If t7 T1/2(2), e-l l2t 0 then: N2=(l l1/l l2) N1,0 e-l l1t=(l l1/l l2)N1 or: l l2 N2=l l1 N1 原子核的衰變規(guī)律原子核的衰變規(guī)律 兩次連續(xù)衰變：兩次連續(xù)衰變：不成平衡不成平衡 129Te - (69 min) 129I -( 1.6 107y) 129Xe(Stable) 103Tc - (50 s) 103Ru - ( 39.4y) 103Rh(Stable) N2=l l1/(l l1-l l2) N1,0 e-l l2t 1- e-(l l1-l l2)t If T1/2(1)

13、l l2, and t7 T1/2(1), then e-(l l1-l l2)t 0 N2=l l1/(l l1-l l2) N1,0 e-l l2t 1 鈾系（4n+2） 238U 234Th 234mPa 234U 230Th 226Ra 222Rn 218Po 214Pb 214Bi 214Po 210Pb 210Bi 210Po 206Pb 原子核的衰變規(guī)律原子核的衰變規(guī)律 1.2 錒系（4n+3） 235U 231Th 231Pa 227Ac 227Th 223Ra 219Rn 215Po 211Pb 211Bi 211Po 207Pb 原子核的衰變規(guī)律原子核的衰變規(guī)律 多次連續(xù)衰

14、變：多次連續(xù)衰變：四個四個放射系 1.3釷系（4n） 232Th 228Ra 228Ac 228Th 224Ra 220Rn 216Po 212Pb 212Bi 212Po 208Pb 原子核的衰變規(guī)律原子核的衰變規(guī)律 多次連續(xù)衰變：多次連續(xù)衰變：四個放射系四個放射系 1.4镎系（4n+1） 241Pu 241Am 237Np 233Pa 233U 229Th 225Ra 225Ac 221Fr 217At 213Bi 213Po 209Pb 209Bi 原子核的衰變規(guī)律原子核的衰變規(guī)律 多次連續(xù)衰變規(guī)律多次連續(xù)衰變規(guī)律 (1) (2) (3) (n) 衰衰 變變 常常 數(shù)數(shù) l l1 l l

15、2 l l3 l ln t=0時的原子數(shù)時的原子數(shù) N1,0 0 0 0 t時刻的原子數(shù)時刻的原子數(shù) N1 N2 N3 Nn dN1/dt=-l l1N1 dN2/dt=l l1N1-l l2N2 dN3/dt=l l2N2-l l3N3 dNn/dt=l ln-1Nn-1-l lnNn Solution: N1=N1,0e-l l1t, N2=l l1/(l l2-l l1) N1,0(e-l l1t- e-l l2t) 代入上式得：代入上式得： N3=l l1l l2N1,0e-l l1t/(l l2-l l1) (l l3-l l1)+ e-l l2t/(l l1-l l2) (l l3

16、-l l2)+ e-l l3t/(l l1-l l3) (l l2-l l3) Nn=l l1l l2l ln-1 N1,0(C1 e-l l1t+C2 e-l l2t+Cn e-l lnt) Where C1=1/(l l2-l l1) (l l3-l l1)(l ln-l l1) C2=1/(l l1-l l2) (l l3-l l2)(l ln-l l2) Cn=1/(l l1-l ln) (l l2-l ln)(l ln-1-l ln) 原子核的衰變規(guī)律原子核的衰變規(guī)律 多次連續(xù)衰變規(guī)律多次連續(xù)衰變規(guī)律 原子核的衰變規(guī)律原子核的衰變規(guī)律 多次連續(xù)衰變規(guī)律多次連續(xù)衰變規(guī)律 T The g

17、eneral diagenetic equations: The 1D advection-diffusion balance: It has the solution: Here c can either be pot. temp., salinity or DIC etc, and c0, c1 and H are three unknowns, to be determined through fitting the observed profiles. (See Walter Munks1966 DSR paper for its application.) 放射性同位素放射性同位素：

18、234Th(24.1 d), 7Be (53.4 d) 化學(xué)行為化學(xué)行為：234Th: particle reactive; 7Be: modest particle reactivity. 來源：來源： 234Th: decay from 238U; 7Be:Naturally produced radio-nuclides formed by cosmic-ray spallation of O and N in the atmosphere. References: a) R. Aller and C. Cochran, 1976, 234Th/238U disequilibrium in the near-shore sediment: particle reworking and diagenetic time scales, Earth and Planetary Science Letters; b) Krishnaswamy et al., 1980; Atmospherically-derived radionuclides