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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. - PowerPoint PPT Presentation
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238U - 206Pb Dating
U23892 Pb206
82 He42
0 e--1+ 8 + 6
t1/2 = 4.468 x 109 years
Assume all 206Pb in a sample is due to 238U decay
206Pb/238U mass ratio gives age
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 mgMass 238U now = 10.67mg Mass 206Pb now = 2.81 mg
U23892 Pb206
82 He42
0 e--1+ 8 + 6
238U - 206Pb Dating (Problem 2 in Group Work)
U23892 Pb206
82 He42
0 e--1+ + 6
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 mgMass 238U now = 10.67mg Mass 206Pb now = 2.81 mg
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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
Mass Spectrometer(See Group Work Problem 4)
Ion abundance
Mass/charge ratio
Molecule ionized by e- beam
Ion abundance
Molecule enters
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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.
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
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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
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…
Field Study Results
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Isotopic signature in wings depends on natal water 2H:1H ratio
different colors = different 2H:1H ratios
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