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Chapter 21

Chapter 21. Radioactivity. Radioactivity- the spontaneous emission of radiation by an unstable atomic nucleus Discovered by Henri Becquerel and the Curies. Nuclear notation. Atomic mass Symbol Atomic number. Detecting radioactivity. Cannot see, hear, smell, taste or touch it.

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Chapter 21

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  1. Chapter 21 Radioactivity

  2. Radioactivity- the spontaneous emission of radiation by an unstable atomic nucleus • Discovered by Henri Becquerel and the Curies

  3. Nuclear notation Atomic mass Symbol Atomic number

  4. Detecting radioactivity • Cannot see, hear, smell, taste or touch it. • Geiger counter • Film badges • Scintillation counter

  5. Types of Radioactive Decay • Alpha, α • Beta, β • Gamma, γ • Decay- the release of radiation by radioactive isotopes

  6. Alpha Decay • Alpha particles • Helium nucleus, 2 protons and 2 neutrons • 42 He 2+ • α • Are large in size, move slowly • Easily stopped by paper or clothing • When an alpha particle is emitted from Uranium, it decays to Thorium

  7. Beta Decay • High energy electron • 0-1 e • β - • Neutron from the nucleus changes into a proton and an electron and the electron is emitted • Are smaller than alpha particles and move faster • Can be stopped by sheets of metal, wood, bricks

  8. Gamma Decay • γ • High energy form of electromagnetic radiation • No mass or charge • Can pass through most materials • Can be stopped by lead or thick concrete • Usually accompanied by other forms of radiation • Most harmful form of radiation

  9. Nuclear Reactions and Energy • Fission- a nuclear reaction in which a nucleus is broken into two or more smaller nuclei, creates a more stable nucleus • Chain reaction- a self-propagating reaction in which uranium absorbs a neutron by bombardment, the nucleus becomes unstable and splits, emitting neutrons and energy • Critical mass- the minimum amount of material needed to sustain a nuclear reaction

  10. Fusion- the process where small nuclei join to form larger nuclei, creates a more stable nucleus • Energy produced from the fusion of 1 kilogram of Hydrogen into Helium to the fission of 1 kilogram of Uranium is 20:1

  11. Nuclear Reactors (fission) • Moderators- used to slow down the speed at which the neutrons collide, can be water, beryllium or graphite • Control rods- rods/ plates that are lowered into the fuel rod assembly to absorb some of the neutrons, controls the rate of reaction

  12. Other uses of nuclear chemistry • Carbon dating • Medical diagnosis and treatment • Tracers • Preserving food

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