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选课名单

选课名单. 一些核素和粒子的质量. Masses of some nuclides ad other particles. 复习与回顾. 核衰变？特点？. 不稳定原子核自发地放出粒子或电磁辐射变成另一种原子核的过程称为核衰变 核衰变是放射性核素的特征核性质，一般情况下不受外界条件，诸如温度、压力、电磁场、化学形态、物理状态等的影响； 核衰变总是伴随着能量的释放（放热过程）. 复习与回顾. 核衰变的主要类型？. Alpha decay ( a decay ) Beta decay ( b decay ) (  + ,  - ,EC)

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选课名单

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  1. 选课名单 C.L.Liu

  2. 一些核素和粒子的质量 Masses of some nuclides ad other particles C.L.Liu

  3. 复习与回顾 • 核衰变？特点？ • 不稳定原子核自发地放出粒子或电磁辐射变成另一种原子核的过程称为核衰变 • 核衰变是放射性核素的特征核性质，一般情况下不受外界条件，诸如温度、压力、电磁场、化学形态、物理状态等的影响； • 核衰变总是伴随着能量的释放（放热过程） C.L.Liu

  4. 复习与回顾 • 核衰变的主要类型？ • Alpha decay ( a decay ) • Beta decay ( b decay ) (+, -,EC) • Gamma decay ( g decay ) • Spontaneous fission • Delayed neutron and proton emission • Two-proton decay • Composite particle emission • Double beta decay C.L.Liu

  5. 复习与回顾 • 填空 210Po()； ()234Th； ()231Th  210Po()206Pb；238U()234Th；235U()231Th C.L.Liu

  6. 复习与回顾 • 能谱与能谱区别？ C.L.Liu

  7. 复习与回顾 • Auger electrons(俄歇电子)？ K俘获过程的另一种伴随粒子是俄歇电子：当一个L层电子跳到K层来填充空位时，可以不发射X射线，而把能量交给另一个L电子，于是这个L电子就会克服结合能而飞出。这种电子叫俄歇电子。 C.L.Liu

  8. 复习与回顾 • Gamma Decay？ • In  decay, electromagnetic radiation is emitted as a nucleus undergoes transitions from its higher excited state (s*) to lower excited state (s1*), or its ground state (sg) C.L.Liu

  9. 放射性衰变 Radioactive Decay

  10. 习题 4 5 C.L.Liu

  11. 习题 6 7 C.L.Liu

  12. 第四讲：放射性衰变 • 放射性衰变的基本规律 衰变常数（） 半衰期（t1/2) 平均寿命 () 活度（A) 比活度（As) • 放射性平衡 长期平衡 暂时平衡 不成平衡 C.L.Liu

  13. I131 8.07d - 0.606 (MeV)  364.5 (keV) Radioactive Decay C.L.Liu

  14. Rn222 3.8235d 5.4895 510 30d RaCl2 Rn(g) 0 4 8 12 16 Time (d) Radioactive Decay C.L.Liu

  15. Law of Radioactive Decay • The law of radioactive decay describes the kinetics of the reaction C.L.Liu

  16. Law of Radioactive Decay : decay constant (衰变常数） C.L.Liu

  17. The decay constant（衰变常数） :单位时间内大量原子核的自发衰变率， 单个原子核在单位时间内的自发衰变几率 在一般情况下，衰变常数与外界条件（诸如温度、压力、外部电磁场等）无关， C.L.Liu

  18. Law of Radioactive Decay • Half-life(t1/2, 半衰期): the time needed for half of a statistically large number of radioactive atoms in a sample to decay. C.L.Liu

  19. The average lifetime（平均寿命） • Average life (t, 平均寿命): the average time needed for an atom to decay; • The time spend for a number of radioactive atoms that has been decreased from N0 to N0/e C.L.Liu

  20. Units of Radioactive Decay（活度） • The expressions of activity are always based on the disappearance of the parent, rather than on the appearance of a product. • 单位时间内母体衰变掉多少的量度，decays/s (dps) • The SI unit of radioactivity(放射性活度) is the becquerel (Bq, 贝克). It is equal to 1 dps. • An older activity unit that is still widely used is the curie (Ci，居里). The curie is defined to be exactly 3.71010 dps (the measured activity of 1g of 226Ra). C.L.Liu

  21. Concepts of the relative levels of activity designated by the Curie unit • Curie Level(居里级)，radioactive samples possessing activity at the Ci level are considered to be very “hot”; that is, highly radioactive. • Millicurie Level(毫居级)，A fairly common working level of radioactivity for tracer studies would be at mCi level(3.7x107 dps). • Microcurie Level(微居级)，at the 1.0-mCi level(3.7x104 dps) exposure risks to personnel are considered to be minimal for most commonly used radioactive tracers. Heavy metal a-particle emitters such as plutonium (Pu) are an exception. C.L.Liu

  22. 放射性活度和比活度 C.L.Liu

  23. 放射性活度和比活度（As) • A=λN，dps, dpm, Ci, • As=A/m • As的单位 固体样品：kBq/g; MBq/g; mCi/g; Ci/g 液体样品： kBq/g; MBq/g; mCi/g; Ci/g 液体（气体）样品： kBq/dm3; mCi/dm3. C.L.Liu

  24. 放射性活度与质量的关系 C.L.Liu

  25. 放射性活度与质量的关系 1mCi的短寿命放射性核素的质量是很小的，而1mCi长寿命放射性核素的质量是可观的。32P(t1/2=14.282d), 1mCi3.510-9g; 238U(t1/2=4.4681010a), 1mCi3kg C.L.Liu

  26. Examples • Example: 99mTc是核医学中常用的放射性核素。其衰变的半衰期是6.01小时。衰变常数为0.115小时-1。计算经过多长时间注射到病人体内的放射性活度减少为开始注射时的0.1%？ 随堂作业 A/A0= 0.1%=0.001， 0.001= e-(0.115/h)(t) ln(0.001) = -(0.115/h)t， t = 60.1 h C.L.Liu

  27. 长期平衡 暂时平衡 不成平衡 放射性平衡 C.L.Liu

  28. Radioactive Equilibriums • A parent will produce one or more radioactive daughters, which will themselves decay into stable or active “granddaughters.” • A parent radionuclide with only one radioactive daughter; • A parent radionuclide producing multiple radioactive daughters. C.L.Liu

  29. 衰变规律 C.L.Liu

  30. C.L.Liu

  31. t1/2(1) >> t1/2(2) (Secular Radioactive Equilibrium) t1/2(1) > t1/2(2) (Transient Radioactive Equilibrium) t1/2(1) < t1/2(2) (non-equilibrium) C.L.Liu

  32. t1/2(1) >> t 1/2(2) Secular Radioactive Equilibrium(长期平衡） A1A2 C.L.Liu

  33. Secular Radioactive Equilibrium • The half-life of the parent is at least 10 times greater than that of the daughter and there is essentially no change in the activity of the parent during the experimental observation. • For decay times that are long with respect to the half-life of the daughter; 5 times the half life • In addition, the decay constant of the long-lived parent will be very small compared to that of the daughter. C.L.Liu

  34. Secular Radioactive Equilibrium C.L.Liu

  35. Practical Applications of S.R.E. C.L.Liu

  36. Practical Applications of S.R.E. • Determination of the long half-life of a mother nuclide by measuring the mass ratio of daughter and mother nuclide; • Calculation of mass ratios of radionuclides that are in SRE; • Calculation of the mass of a mother nuclide from the measured activity of a daughter nuclide. • The radioactive daughter source. C.L.Liu

  37. Transient Equilibrium • The half-life of the parent is approximately 3-10 times longer than that of the daughter, but is short enough so there is a measurable decay of the parent during the experiment. • After 3-5 half-lives of the daughter nuclide, the term e-l2twill become very small and can be ignored. C.L.Liu

  38. Transient Equilibrium (暂时平衡） C.L.Liu

  39. C.L.Liu

  40. Half-life of Mother Nuclide shorter than Half-life of Daughter Nuclide C.L.Liu

  41. 218Po()214Pb(-) 218Po C.L.Liu

  42. The change of total activity with different 1/2. C.L.Liu

  43. Similar Half-lives C.L.Liu

  44. Parent with Multiple Radioactive daughters • There are many radionuclides that decay to produce a sequence of radioactive daughters. C.L.Liu

  45. 多子体衰变Parent with Multiple Radioactive daughters • Bateman equation • Two assumptions: • Only the parent is present at t = 0; • No two decay constants in the chain are equal. When t=0 N1(0)=N1，0 N2(0)=N3(0)=N4(0)=0 C.L.Liu

  46. Parent with Multiple Radioactive daughters C.L.Liu

  47. Parent with Multiple Radioactive daughters C.L.Liu

  48. Parent with Multiple Radioactive daughters Example: A sample of 222Rn has an activity of 1.00 Ci. Calculate the activity of the daughter nuclide214Pb after 1.00 h. The decay is C.L.Liu

  49. The number of atoms of the parent nuclide, 222Rn, is C.L.Liu

  50. C.L.Liu

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