海洋中的放射化学

1、主讲：蔡平河 电话：2880179；e-mail: C 高级海洋化学 （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 核衰变类型核衰变类型 alpha alpha衰变衰变 HeYX HeRnRa A Z A Z 4 2 4 2 4 2 222 86 226 88 核衰变类型核衰变类型 Beta Beta衰变衰变 YX PoBi A Z A Z1 210 84 210 83 ：衰变 YX BC A Z A Z1 1111 衰变： 核衰变类型核衰变类型 Beta Beta衰变衰变 YX LiBe A Z ECA Z EC 1 77 电子俘获： 核衰

8、变类型核衰变类型 Beta Beta衰变衰变 原子核的衰变规律原子核的衰变规律 原子核的衰变规律原子核的衰变规律 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 原子核的衰变规律原子核的衰变规律 衰变常数、半衰期和平均寿命衰变常数、半衰期和平均寿命 衰变常数衰变常数：-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 平均寿命平均寿命： =1/l l or =1.44 T1/

9、2 原子核的衰变规律原子核的衰变规律 放射性活度及其单位放射性活度及其单位 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 单位：单位：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; 原子核的衰变规律

10、原子核的衰变规律 两次连续衰变 90Sr - 90Y - 90Zr(Stable) 95Zr - 95Nb - 95Mo(Stable) 99Mo - 99mTc 99Tc(Stable) 113Sn - 113mIn 113In(Stable) A B C (稳定稳定) 半衰期半衰期 T1/2(1) T1/2(2) 衰变常数衰变常数 l l1 l l2 0 t=0 N1,0 0 0 t=t N1 N2 N3 对于对于A: N1=N1,0 e-l l1t ; -dN1/dt=l l1 N1 对于对于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) 两次连续衰变两次连续衰变 原子核的衰变规律原子核的衰变规律 两次连续衰变：暂时平衡两次连续衰变：暂时平衡 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足够长时足够长时, 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 原子核的衰变规律原子核的衰变规律 两次连续衰变：两次连续衰变：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 铀系（4n+2） 238U 234Th 234mPa 234U 230Th 226Ra 222Rn 218Po 214Pb 214Bi 214Po 210Pb 210Bi 210Po 206Pb 原子核的衰变规律原子核的衰变规律 1.2 锕系（4n+3） 235U 231Th 231Pa 227Ac 227Th 223Ra 219Rn 215Po 211Pb 211Bi 211Po 207Pb 原子核的衰变规律原子核的衰变规律 多次连续衰

14、变：多次连续衰变：四个四个放射系 1.3钍系（4n） 232Th 228Ra 228Ac 228Th 224Ra 220Rn 216Po 212Pb 212Bi 212Po 208Pb 原子核的衰变规律原子核的衰变规律 多次连续衰变：多次连续衰变：四个放射系四个放射系 1.4镎系（4n+1） 241Pu 241Am 237Np 233Pa 233U 229Th 225Ra 225Ac 221Fr 217At 213Bi 213Po 209Pb 209Bi 原子核的衰变规律原子核的衰变规律 多次连续衰变规律多次连续衰变规律 (1) (2) (3) (n) 衰衰 变变 常常 数数 l l1 l l

15、2 l l3 l ln t=0时的原子数时的原子数 N1,0 0 0 0 t时刻的原子数时刻的原子数 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) 原子核的衰变规律原子核的衰变规律 多次连续衰变规律多次连续衰变规律 原子核的衰变规律原子核的衰变规律 多次连续衰变规律多次连续衰变规律 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) 化学行为化学行为：234Th: particle reactive; 7Be: modest particle reactivity. 来源：来源： 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