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Changes in the Nucleus

Changes in the Nucleus. A Puzzling Question. Why don’t the protons in the nucleus push out each other?. What makes nucleus stable. Strong nuclear force The neutron-to-proton ratio: (a) More protons there are, more neutrons required → Higher the atomic number, higher the ratio

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Changes in the Nucleus

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  1. Changes in the Nucleus

  2. A Puzzling Question Why don’t the protons in the nucleus push out each other?

  3. What makes nucleus stable • Strong nuclear force • The neutron-to-proton ratio: (a) More protons there are, more neutrons required → Higher the atomic number, higher the ratio (Ex) For Ca, the ratio ≈ 1; for Hg, the ratio ≈ 1.5

  4. (b) If too many neutrons, neutrons transform to protons by emitting beta particles (Ex) (c) If not enough neutrons, protons transform to neutrons by capturing electrons (Ex) (d) During the nucleus change, mass is NOT conserved → the difference in mass transforms to energy, E = mc2

  5. Transmutation Reactions • Transmutation = changing one element to another • Two ways of transmutation • Occur naturally (called nuclear decay) • By bombarding the nucleus with neutrons, protons, or alpha particles (Ex) • All the transuranium elements undergo transmutation • Transuranium elements: elements with atomic numbers above 92 (uranium)

  6. Nuclear Reactions • Radioactivity: emission of rays or particles when a change occurs in the nucleus ** Chemical reactions are due to transfer of electrons from an atom to an atom • Two ways to change the nucleus: by particle capture or particle emission • Radiation: rays or particles emitted from the change in the nucleus • alpha, beta, gamma • Other particles such as positron, neutron

  7. Types of Radiation Other particles: positron ( ), neutron( )

  8. Writing Nuclear Equations • Nucleus decay • Starting atom → Ending atom + Radiation particle • Bombardment with or absorption of radiation particle • Starting atom + Radiation particle → Ending atom • Rules to follow • The total atomic mass number is conserved • The total atomic number is conserved (Ex) Write a nuclear equation: (1) for the alpha decay of gold-185 (Z= 79) (2) for the beta decay of sodium-24 (Z= 11) (3) for the bombardment of uranium-238 (Z = 92)with a neutron

  9. Practices • ? + 10n ---> 249Bk + 0-1e • 20Ne + ? ---> 24Mg + γ • 2713Al + 42He → 3015P +?

  10. Fusion vs. Fission 1) Fusion: fusing smaller nuclei to become a larger nucleus (Ex) 1H + 1H  2He 2) Fission: breaking a large nucleus to smaller nuclei (Ex) 92U  36Kr + 56Ba

  11. Chain Reaction

  12. Nuclear Energy • Results when some mass in the nucleus converts to energy • E = mC2 E = energy m = mass C = speed of light, 3.0x108 m/sec (Ex) Amount of energy from 1 gram (0.035 oz) of matter E = 0.001 kg x (3.0 x 108 m/sec)2 = 9 x 1013 kgm2/sec2 = 9 x 1013 J ≈ 9 x 1010 candy bars

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