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More Nuclear Chemistry

More Nuclear Chemistry. Abundance Binding Energy Fission Isotopic Signatures. Nuclear Binding Energy Two Ways. Nuclear Rxn Energy from BE. Molar BE and Element Abundance (Group Work Problem 1). + 8. + 6. 0 e-. 4. -1. He. 2. 238. 206. U. Pb. 92. 82. 238 U - 206 Pb Dating.

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More Nuclear Chemistry

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  1. More Nuclear Chemistry Abundance Binding Energy Fission Isotopic Signatures

  2. Nuclear Binding Energy Two Ways

  3. Nuclear Rxn Energy from BE

  4. Molar BE and Element Abundance (Group Work Problem 1)

  5. + 8 + 6 0 e- 4 -1 He 2 238 206 U Pb 92 82 238U - 206Pb Dating • t1/2 = 4.468 x 109 years • Assume all 206Pb in a sample is due to 238U decay • 206Pb/238U mass ratio gives age

  6. + 8 + 6 0 e- 4 -1 He 2 238 206 U Pb 92 82 238U - 206Pb Dating (Problem 2 in Group Work) • age = n*length of one half life • So, we must find n (how many half lives of 238U have passed) • (N/No) = (1/2)n or log10(N/No) = n[log10(1/2)] or ln(N/No)=n[ln(1/2)] • We know N = 10.67 mg • How can we find No? Mass 238U originally ? Mass 206Pb originally = 0 mg Mass 238U now = 10.67mg Mass 206Pb now = 2.81 mg

  7. + + 6 0 e- 4 -1 He 2 238 206 U Pb 92 82 238U - 206Pb Dating (Problem 2 in Group Work) • How can we find No? • Mass 238U that produced 2.81mg of 206Pb = 2.81mg(238/206) = 3.25mg • Original mass 238U = 3.25 mg + 10.67 mg = 13.92 mg • log10(10.67/13.92) = n[-0.301]; n = 0.383 half lives • age = n* t1/2 = (0.393)(4.468 x 109 yrs/half life) = 1.71 x 109 years Mass 238U originally = 13.92mg Mass 206Pb originally = 0 mg Mass 238U now = 10.67mg Mass 206Pb now = 2.81 mg

  8. Nuclear Fission (Consider This 3.53/Problem 3 in Group Work)

  9. Time and Temp Since the Big Bang(Group Work Problem 6)

  10. Isotopic Signatures

  11. Deuterium Occurs Naturally in Water 1H : 2H ratio in H2O varies slightly with location ratio is an isotopic signature and can be used as a tracer

  12. Mass Spectrometer(See Group Work Problem 4) Molecule ionized by e- beam Molecule enters Ion abundance Ion abundance Mass/charge ratio

  13. Isotopic Signatures in Tracing H2O plants animals 1H : 2H in H2O affects 1H : 2H in organism’s H-compounds, so you can trace where an organism has come from by looking at the 1H : 2H of its H-compounds.

  14. Problem in Conservation Biology: How to protect monarch butterfly populations? Correlate natal sites in North America with wintering sites in Mexico. • focus conservation efforts on most important sites

  15. Experiment • Rear monarchs in • lab on milkweeds gown with known 2H concentration water • field on milkweeds naturally watered by rainfall • Use mass spectrometry to analyze wings for 2H:1H ratio

  16. Results • Lab monarch study: • isotope signature in wings highly correlates to isotope signature of water so isotope signature is a good way to trace where the butterflies originated • Field monarch study: • isotope signatures vary depending on site…

  17. Field Study Results Isotopic signature in wings depends on natal water 2H:1H ratio different colors = different 2H:1H ratios

  18. Natal Origins of Monarch Butterflies Found Wintering in Mexico Isotope signature studies of wings suggest that few butterflies found in Mexico originate in Canada

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