The Nucleus: A Chemist’s View

1. The Nucleus: A Chemist’s View Nuclear Stability and Radioactive • Thermodynamic stability－ potential energy • Kinetic stability－radioactive decay

2. Nuclide • A nuclide is a type of atom characterized by its proton number, neutron number and its energy condition. • Nuclides with identical proton number but differing neutron number are called isotopes. • Conditions with a life of less than 10-10s are called excited conditions of a nuclide. • At present, more than 2,770 different nuclides are known, distributed over the 113 currently known elements, only 279 are stable with respect to radioactive decay.

4. Known nuclides • All nuclides with 84 or more protons are unstable with respect to radioactive decay. • Light nuclides are stable when (A-Z)/Z ratio is 1. • For heavier elements for stability, (A-Z)/Z ratio is greater than 1 and increases with Z.

5. Magic numbers: 2, 8, 20, 28, 50, 82, 126 • Specific numbers of protons or neutrons produce especially stable nuclides.

6. Types of Radioactive Decaya-particle production The common modes of decay • Spontaneous fission • The splitting of a heavy nuclide into two lighter nuclides with similar mass numbers. • Slow rate for most nuclides

7. Types of Radioactive Decayb-particle production The common modes of decay • The net effect of b-particle production is to change a neutron to a proton. • The nuclides lie above the zone of stability. • The ratios of neutron/proton are too high.

8. Types of Radioactive Decayg-ray production • high-energy photon • g-ray production accompanies unclear decays and particle reaction. • The emission of g rays is one way a nucleus with excess energy can relax to its ground state.

9. Types of Radioactive Decaypositron production • The net effect of this process is to change a e a protonto a neutron. • Higher neutron/proton ratio • Nuclides lie below the zone of stability.

10. Antiparticle Matter-antimatter collisions, is called annihilation.

12. Often a radioactive nucleus cannot reach a stable state through a single decay process. Decay series

13. The Kinetic of Radioactive Decay • First order reaction

14. The decay of a 10 g sample of Sr-90

15. Change in the amount of Mo with time

17. Nuclear Transformations • The conversion of one element into another

18. Experiments for Nuclear Transformationscyclotron Particle accelerators

19. Diagram of a linear accelerator

21. Detection of Radioactivity Geiger-Muller counter

22. Carbon-14 Dating

23. Drawbacks of Radiocarbon Dating • Errors up to 3000 years may have occurred. (Measurements of U/Th ratio development) • Large piece of the object must be burned. (Use mass spectrometry)

25. Figure 21.8: Consumption of Na131I Source: Visuals Unlimited

26. Thermodynamic Stability of the Nucleus

27. Energy for per Nucleon • The energy required to decompose this nucleus into its components has same numeric value but is positive. • This is called the binding energy per nucleon.

28. Binding energy per nucleon as a function of mass number.

29. Fusion: Combining two light nuclei to form a heavier, more stable nucleus. Fission: Splitting a heavy nucleus into two nuclei with smaller mass numbers. Nuclear Fission and Nuclear Fusion

30. Nuclear Fission and Nuclear Fusion

31. Nuclear Fission

32. Neutrons are also produced in the fission reactions. Chain reaction－This makes it possible to produce a self-sustaining fission process. Chain Reaction

33. Subcritical • For the fission reaction, at least one neutron from each fission event must go on to split another nucleus. • Subcritical－If, on the average, less than one neutron causes another event, the process dies out.

34. Critical • If exactly one neutron from each fission event causes another fission event, the process sustains itself at the same level.

35. If more than one neutron from each fission event causes another fission event, the process rapidly escalates and the heat buildup causes a violent explosion. Supercritical

36. Schematic diagram of a nuclear power plant

37. Schematic of a reactor core

38. Nuclear Fusion • Bind two protons together. • A temperature of 4×107 K is required.

39. A schematic diagram of the tentative plan for deep underground isolation of nuclear waste.