Radioactivity

1. Radioactivity

2. RADIATION *Penetrating rays emitted by a radioactive source *Ranges from Cosmic and Gamma Rays to Radio Waves

4. RADIOACTIVE DECAY *Unstable atoms have excess internal energy. *the nucleus can undergo a spontaneous change towards a more stable form.

5. 3 types of RADIATION α – radiation (alpha radiation) ß– radiation (beta radiation) γ – radiation (gamma radiation)

6. 4 2 42 He α or α – decay: *Emission of an α – particle *Particle is a Helium nucleus *Element changes to a new element – a Transmutation occurs

7. 234 92 230 90 4 2 He Th U + α – decay equation Atomic mass decreases by 4 Atomic number decreases by 2

8. α – decay 4 2 226 88 Ra 222 86 Rn He +

9. α – decay *Particle carries a positive charge *Large, heavy particle - moves slowly *Little penetrating power *stopped by skin or a sheet of paper

10. o -1 0 -1 e ß or ß -decay *Emission of a beta - particle *Particle is an electron *A transmutation occurs - a neutron changes into a proton and an electron

11. 14 6 14 7 o -1 C N e + ß -decay equation *Atomic mass stays the same *Atomic number increases by 1

12. ß -decay

13. ß -decay *Particle carries a negative charge *Small, light-weight particle *fast-moving *Penetrates 1-2 cm of skin or water *can be stopped by metal sheet a few mm thick

14. γ – radiation Emission of electromagnetic energy from an atom’s nucleus No particles are emitted A transmutation does not occur

15. γ – radiation Identical to X-rays Energy transmitted in waves Great penetrating power - can pass through human body

16. γ – radiation *Thick barriers of lead, concrete, or water are used as protection against them

17. Too many protons and neutrons Tend to alpha decay Too many neutrons Tend to beta decay Graph of unstable nuclei Too many protons Capture e- to convert p+ to n0

18. Many radioactive elements have to go through a series of decays to reach a stable isotope

19. Detecting Radiation Radiation is ionizing radiation – it knocks electrons off of the substances it hits to produce ions Instruments can detect this process

20. Detecting Radiation Geiger counter – uses gas to detect radiation. Ionized gas particles conduct electricity and produce audible clicks

21. Detecting Radiation Scintillation counter - uses phosphor to detect radiation Phosphors produce flashes of light when hit by ionizing radiation

22. Detecting Radiation Film badge – uses photographic film to detect radiation Worn by personnel working near radiation sources to monitor exposure

23. Half – life The Half-life is the time it takes for half of the atoms of a radioactive substance to decay. After one half-life the level of radioactivity of a substance is halved, after two half-lives it is reduced to one quarter, and so on

24. Half-life Graph

25. Fission Fission is a nuclear process in which a heavy nucleus splits into two smaller nuclei after being bombarded with neutrons 1 0 n 142 56 Ba 1 0 n 1 0 n 235 92 236 92 U + U + n 1 0 91 36 Kr

26. Fission Reaction

27. Fission reactions Controlled fission is used in Nuclear Reactors to produce useful energy

28. Fusion Fusion occurs when two nuclei combine to produce a nucleus with a heavier mass 2 1 H 3 1 4 2 1 0 n + H He + + energy

29. Fusion Reaction Fusion reactions release more energy then fission reactions