What do we mean by Radioactivity?

1. What do we mean by Radioactivity? Radioactive decay is the process in which an unstable atomic nucleus loses energy by emitting radiation in the form of particles or electromagnetic waves. There are numerous types of radioactive decay. The general idea: An unstable nucleus releases energy to become more stable

2. A Review of Atomic Terms • nucleons – particles found in the nucleus of an atom • neutrons • protons • atomic number (Z) – number of protons in the nucleus • mass number (A) – sum of the number of protons and neutrons • isotopes – atoms with identical atomic numbers but different mass numbers • nuclide – each unique atom

3. A. Radioactive Decay • radioactive – nucleus which spontaneously decomposes forming a different nucleus and producing one or more particles • nuclear equation – shows the radioactive decomposition of an element

4. Radioactive Decay Radioactive decay results in the emission of either: • an alpha particle (a), • a beta particle (b), • or a gamma ray(g).

5. 222 Rn 226 86 Ra 88 4 He 2 Alpha Decay

6. Beta Decay As a result of beta decay, the nucleus has one less neutron, but one extra proton. The atomic number, Z, increases by 1 and the mass number, A, stays the same.

7. 218 218 Po At 85 84 0 b -1 Beta Decay

8. A. Types of Radioactive Decay • Alpha Decay • Alpha-particle production • Alpha particle – helium nucleus • Examples • Net effect is loss of 4 in mass number and loss of 2 in atomic number.

9. A. Types of Radioactive Decay • Beta Decay • Beta-particle production • Beta particle – electron • Examples • Net effect is to change a neutron to a proton.

10. A. Radioactive Decay • Gamma Emission • Gamma ray release • Gamma ray – high energy photon • Examples • Net effect is no change in mass number or atomic number.

11. A. Types of Radioactive Decay • Positron Emission • Positron production • Positron – particle with same mass as an electron but with a positive charge • Examples • Net effect is to change a proton to a neutron.

12. A. Types of Radioactive Decay • Electron Capture • An electron is captured from the lower energy orbitals. (first shell) • Example

13. A. Radioactive Decay • Decay series

14. Kinds of Radioactivity The three main decays are Alpha, Beta and Gamma

15. Early Pioneers in Radioactivity Rutherford: Discoverer Alpha and Beta rays 1897 Roentgen: Discoverer of X-rays 1895 The Curies: Discoverers of Radium and Polonium 1900-1908 Becquerel: Discoverer of Radioactivity 1896

16. A. Radioactive Decay

17. B. Nuclear Transformations • Nuclear transformation –change of one element to another • Bombard elements with particles – Examples

18. B. Nuclear Transformations • Transuranium elements – elements with atomic numbers greater than 92 which have been synthesized

19. C. Detection of Radioactivity and the Concept of Half- life • Geiger-Muller counter – instrument which measures radioactive decay by registering the ions and electrons produced as a radioactive particle passes through a gas-filled chamber

20. C. Detection of Radioactivity and the Concept of Half- life • Scintillation counter – instrument which measures the rate of radioactive decay by sensing flashes of light that the radiation produces in the detector

21. C. Detection of Radioactivity and the Concept of Half- life • Half-life – time required for half of the original sample of radioactive nuclides to decay

22. Objectives • To learn how objects can be dated by radioactivity • To understand the use of radiotracers in medicine

23. A. Dating by Radioactivity • Radiocarbon dating • Originated in 1940s by Willard Libby • Based on the radioactivity of carbon-14 • Used to date wood and artifacts

24. B. Medical Applications of Radioactivity • Radioactive nuclides that can be introduced into organisms and traced for diagnostic purposes. • Radiotracers

25. Objectives • To introduce fusion and fission as sources of energy • To learn about nuclear fission • To understand how a nuclear reactor works • To learn about nuclear fusion • To see how radiation damages human tissue

26. A. Nuclear Energy • Two types of nuclear processes can produce energy • Combining 2 light nuclei to form a heavier nucleus - fusion • Splitting a heavy nucleus into 2 nuclei with smaller mass numbers - fission

27. B. Nuclear Fission • Releases 2.1 1013 J/mol uranium-235 • Each fission produces 3 neutrons

28. B. Nuclear Fission • Chain reaction – self sustaining fission process caused by the production of neutrons that proceed to split other nuclei • Critical mass – mass of fissionable material required to produce a chain reaction

29. B. Nuclear Fission

30. C. Nuclear Reactors

31. C. Nuclear Reactors • Reactor core

32. D. Nuclear Fusion • Process of combining 2 light nuclei • Produces more energy per mole than fusion • Powers the stars and sun

33. D. Nuclear Fusion • Requires extremely high temperatures • Currently not technically possible for us to use as an energy source

34. E. Effects of Radiation • Factors Determining Biological Effects of Radiation • Energy of the radiation • Penetrating ability of the radiation • Ionizing ability of the radiation • Chemical properties of the radiation source

35. E. Effects of Radiation

36. E. Effects of Radiation