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Chapter 18: Radioactivity

6. Li. 3. Chapter 18: Radioactivity. Protons and neutrons are held together in nucleus by the strong force . The strong force is strong enough to cancel out the electrical repulsion between protons in small nuclei. Strong force. p/p repulsion. Net force. Strong force. 6. Li. 3.

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Chapter 18: Radioactivity

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  1. 6 Li 3 Chapter 18: Radioactivity Protons and neutrons are held together in nucleus by the strong force. The strong force is strong enough to cancel out the electrical repulsion between protons in small nuclei.

  2. Strong force p/p repulsion Net force Strong force 6 Li 3 P/p repulsion stronger Net force weaker

  3. Isotopes: Atoms of the same element (same atomic number=same number of protons), but different numbers of neutrons ( different mass numbers). 1 2 3 H H H 1 1 1 hydrogen deuterium tritium As the number of neutrons in an isotope increases, the stability of the nucleus decreases due to a decrease in the strong force that holds the nucleus together. Normal hydrogen and deuterium are not radioactive, while tritium is.

  4. 14 12 6 6 Atomic number: the number of protons Mass number: the number of protons added to the number of neutrons C C 6 p 6 p 14 - 6 = 8 n 12 - 6 = 6 n

  5. Nuclear decay

  6. 4 0 He e 2 -1 The most common types of radiation given off by unstable nuclei are: or  Alpha particles: helium nuclei Beta particles: electron emitted FROM THE NUCLEUS (are 10x more penetrating than a) or  g Gamma rays: high frequency electromagnetic radiation (are 1000x more penetrating than a)

  7. Example of alpha particle decay: 210 4 Po He 84 2 206 Pb + 82 *decay = giving off a particle Notice that there are 84 protons on both sides of the arrow. The Law of Conservation of Mass strikes again!! Transmutation: the changing of one element into another. • When Po decays to Pb by alpha particle emission, it has transmutated.

  8. 131 0 I e 53 -1 137 Ba 56 0 e -1 Ex: I-131 undergoes beta decay: 131 + Xe 54 • When the nucleus loses an electron, it comes from a neutron. Since the neutron has lost a -1 charge, it becomes a proton with a +1 charge. Ex: Ba-137 undergoes electron capture: 137 + Cs 55

  9. sUn Spl tting  t nier U U Sm shing  h ger  U He Te + + Zr + H H + + U Nuclear F i ssion vs. Nuclear F u sion

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