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Radioactivity II

Radioactivity II. Decay Series. A radioactive nucleus usually goes through several decay processes before reaching a stable state Ex/ Uranium-235 undergoes several decays before ending up as stable Lead-206. Decay Series—Uranium-235. α. What type of Decay?.

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Radioactivity II

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  1. Radioactivity II

  2. Decay Series • A radioactive nucleus usually goes through several decay processes before reaching a stable state • Ex/ Uranium-235 undergoes several decays before ending up as stable Lead-206

  3. Decay Series—Uranium-235 α What type of Decay? (Hint: A decreased by 4 and Z decreased by 2!) (A) (Z)

  4. Half-Life • If N = # of nuclides in a given sample: The Rate of Decay is: Rate = -∆N = kN ∆t Integrated: ln(N/N0) = -kt(N0= initial # nuclides at t=0) Half Life: time required for the N = N0/2 so: ln(2)/k = t1/2 or 0.693/k = t1/2 (k = rate constant for decay)

  5. Carbon-14 Dating • Uses ½ life of C-14  5730 years (good for ~3 half-lives!) Ancient fire wood: decay rate = 3.1 counts/min Fresh-cut wood: decay rate = 13.6 counts/min Rate = kN kN/kN0 = N/N0 = 3.1 counts/min∙g = 0.23 13.6 counts/min∙g k = 0.693/t1/2 = 0.693/5730 years ln(N/N0) = ln(0.23) ln(N/N0) = -kt  ln(0.23) = -(0.693/5730 years)t t = 12,000years

  6. Nuclear Fission and Fusion • Fission: The splitting of a heavy nucleus into two nuclei with smaller mass numbers

  7. Nuclear Fission and Fusion • Fusion: The combination of two light nuclei into a heavier, more stable nucleus. Energy

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