1 / 41

Nucleosynthesis of the nuclides

Nucleosynthesis of the nuclides. Chart. 2 nd Generation Stars (Our Sun) Fusion by CNO reaction. 12 C + 1 H  13 N + g 13 N  13 C + b + + v 13 C + 1 H  14 N + g 14 N + 1 H  15 O + g 15 O  15 N + b + + v 15 N + 1 H  12 C + 4 He.

willow
Download Presentation

Nucleosynthesis of the nuclides

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Nucleosynthesis of the nuclides

  2. Chart

  3. 2nd Generation Stars (Our Sun)Fusion by CNO reaction 12C + 1H 13N + g 13N 13C + b+ + v 13C + 1H 14N + g 14N + 1H 15O + g 15O 15N + b+ + v 15N + 1H 12C + 4He 12C + 4 1H 12C + 3 g + 2 b+ + 2 v

  4. Then by combustion of 16O ( < 1 yr), a reaction that produces higher mass elements, including Si and Mg 16O + 16O 28Si + 4He + g 12C + 16O 24Mg + 4He + g chart

  5. Fusion is limited at mass 56Fe by the diminishing return of energy of fusion and increased energy of nuclear bonds p = proton = 1.007593 u = 1.6726234 E–27 kg n = neutron = 1.008982 u = 1.6749287 E–27 kg u = 1 atomic mass unit = 1/12 12C = 1.660018 E–27 kg 5626Fe30 = 26p + 30n A 56Fe = 56 Mais le poid atomique de 56Fe = 55.934942 (http://csnwww.in2p3.fr/AMDC/web/masseval.html) 26 x 1.007593 = 26.197418 u 30 x 1.008982 = 30.269460 u 56.466878 u 56.466878 – 55.934942 = 0.531936 u = 0.883 E–27 kg = masse perdue Converti en énergie de liason nucléaire: E = mc2

  6. Energy of nuclear bonding • maximum at 56Fe • beyond, fusion is an endothermic reaction • nucleosynthesis beyond 56Fe by neutron capture reactions and by fission of the nuclides with Z > 90 (uranium and the transuranics) http://www.chem.uidaho.edu/~honors/nucbind.html

  7. End as a red giant and a supernova

  8. Supernova remnants Cygnus Loop (HST): green=H, red=S+, blue=O++ Cas A in x-rays (Chandra) Vela Remnant of SN386, with central pulsar (Chandra) SN1998bu

  9. Nucleosynthsis in 2nd generation stars:Inventory – 1H, 4He, 12C, 13C, 14N, 15N, 16O, 20Ne, 24Mg, 28Si, 32S,36Ar,40Ca, 44Ca,48Ti,52Cr,56FeProduction of neutrons: 13C + 4He 16O + n

  10. Nucleosynthesis by neutron and proton capture Process S – slow neutron capture (2nd generation stars) Production of elements up to Bi Process R – capture of fast neutrons (red giants) Production of heavy elements – to U. After is limited by fission Process P – proton capture (1H) Production of nuclides poor in neutrons s

  11. The Stable Environmental Isotopes Isotope Ratio % natural Reference abundance 2H 2H/1H 0.015 VSMOW 3He 3He/4He 0.000138 Atmospheric He 13C 13C/12C 1.11 VPDB 15N 15N/14N 0.366 AIR N2 18O 18O/16O 0.204 VSMOW, VPDB 34S 34S/32S 4.21 CDT 37Cl 37Cl/35Cl 24.23 SMOC

  12. Routine and non-routine stable environmental isotopes

  13. Delta - permil: d - ‰ ‰ VSMOW

  14. What is the relative enrichment or depletion of 18O in crustal rocks (~0.204%) relative to VSMOW = 17.4‰ VSMOW  crustal rocks are enriched in 18O by 17.4‰ or 1.7% relative to the standard VSMOW

  15. Isotope Ratio Mass Spectrometry

  16. Laser attenuation isotope analyser(Wavelength-Scanned Cavity Ring Down Spectroscopy – WS-CRDS) Laser absorption Reads fraction of heavy isotope bonds Direct reading of BOTH 18O and D ratios Do it in the field! New!

  17. Los Gatos – the original black box Laser attenuation isotope analyser(Wavelength-Scanned Cavity Ring Down Spectroscopy – WS-CRDS) and Picarro – nice small footprint

  18. Laser attenuation isotope analyser(Wavelength-Scanned Cavity Ring Down Spectroscopy – WS-CRDS) Check out the sample requirements – 2 mL. Fill a tray of 100! – lots of good data.

  19. Distribution of isotopes in nature • Isotope fractionation during reaction • Rayleigh distillation during reservoir depletion

  20. Isotope fractionation, a

  21. Physico-chemical fractionation

  22. Isotope partitioning functions  = symmetry value m = mass of isotope E = the energy state summed from the zero-point to the energy of the dissociated molecule (J·mole–1) k = Boltzmann constant (gas constant per molecule) = n · 1.380658 · 10–23 JK–1 T = thermodynamic temperature K

  23. Diffusive fractionation v = molecular velocity (cm · s–1) k = Boltzmann constant (gas constant per molecule) = n · 1.380658 · 10–23 JK–1 m = molecular mass (e.g. 7.3665 · 10–26 kg for 12C16O2) T = absolute temperature K

  24. Diffusive Fractionation e.g. 13C during CO2 diffusion Diffusion in a vacuum Diffusion in air

  25. Metabolic (biologic) Fractionation • 13C during photosynthesis • sulphate reduction • methanogenesis . . .

  26. Units Isotope Enrichment (e) • Isotope difference in permil units between two reacting phases at equilibrium • when a is small, then we can use:

  27. Units Isotope Separation (D) • Isotope difference in permil units between any two phases

  28. For a water – vapor exchange at 25°C what is the d18O of vapor, where: • water d18Ow = 0.0 ‰ VSMOW

  29. For a water – vapor exchange at 25°C what is the d18O of vapor, where: • water d18Ow = 0.0 ‰ VSMOW The fractionation factor (a) is: a18Ow-v = 1.0093 The isotopic enrichment (e): e18Ow-v = (a–1) ·103 = 9.3‰ and e18Ov-w = – 9.3‰

  30. For a water – vapor exchange at 25°C what is the d18O of vapor, where: • water d18Ow = 0.0 ‰ VSMOW e18Ow-v = (a–1) ·103 = 9.3‰ d18Ovapor = d18Owater – e18Owater-vapor = 0.0 – 9.3‰ = – 9.3‰ • vapor d18Ov = –9.30‰ VSMOW

  31. For most reactions in hydrogeology: • d values are typically –50 to +50 ‰ • a values are close to 1 (0.98 to 1.02) • e values are typically –20 to +20 ‰ Except for some extreme reactions and light isotopes . . . e.g. hydrogen gas produced from water is strongly depleted in 2H and has a fractionation factora2HH2O-H2 = 3.76 at 25°C. What will be the d2H value for H2 produced from water with d2HH2O = –75‰ at 25°C?

  32. d2HH2 = –754‰ VSMOW (but using e, d2HH2 = –75 – 2760 = –2835‰)

  33. So, use the e simplification . . . • when a is close to 1 • when the d-values are not too different from the reference (i.e. within a few tens of permil of 0)

  34. Fractionation and Temperature lnaX-Y = aT–2 + bT–1 + c

  35. Fractionation and Temperature

  36. e D ‰ 60 80 100 120 140 160 40 40 30 30 2 H w-v 20 20 18 O w-v 10 10 T °C T °C 0 0 2 H i-v 18 -10 O -10 i-v -20 -20 8 10 12 14 16 18 18 e O ‰ Fractionation and Temperature

  37. Fractionation - Other Systems

More Related