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)

238 U Pb Dating U Pb He e t 1/2 = x 10 9 years Assume all 206 Pb in a sample is due to 238 U decay 206 Pb/ 238 U mass ratio gives age

238 U Pb Dating (Problem 2 in Group Work) age = n*length of one half life So, we must find n (how many half lives of 238 U have passed) (N/N o ) = (1/2) n or log 10 (N/N o ) = n[log 10 (1/2)] or ln(N/N o )=n[ln(1/2)] We know N = mg How can we find N o ? Mass 238 U originally ? Mass 206 Pb originally = 0 mg Mass 238 U now = 10.67mg Mass 206 Pb now = 2.81 mg U Pb He e

238 U Pb Dating (Problem 2 in Group Work) U Pb He e How can we find N o ? Mass 238 U that produced 2.81mg of 206 Pb = 2.81mg(238/206) = 3.25mg Original mass 238 U = 3.25 mg mg = mg log 10 (10.67/13.92) = n[-0.301]; n = half lives age = n* t 1/2 = (0.393)(4.468 x 10 9 yrs/half life) = 1.71 x 10 9 years Mass 238 U originally = 13.92mg Mass 206 Pb originally = 0 mg Mass 238 U now = 10.67mg Mass 206 Pb now = 2.81 mg

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

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

Isotopic Signatures

Deuterium Occurs Naturally in Water 1 H : 2 H ratio in H 2 O 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

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

Experiment Rear monarchs in lab on milkweeds gown with known 2 H concentration water field on milkweeds naturally watered by rainfall Use mass spectrometry to analyze wings for 2 H: 1 H 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 Isotopic signature in wings depends on natal water 2 H: 1 H ratio different colors = different 2 H: 1 H ratios

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