Astrophysical Nucleosynthesis

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1 R. D. Gehrz ASTRO 2001, Fall Semester RDG

2 The Chemical Evolution of the Universe 2RDG 1

3 The Stellar Evolution Cycle 3 RDG

4 a v a v X X V = v a + v X 4 RDG

5 reaction rate r n n s cm ax a X r r ( E) ax ax # ( E) from E ax where ax 2 ( E) from penetration probability e Energy released per reaction E ergs Energy generation coeffient m m 5 RDG m a a X m X 4 2 Z Z e 2 a hv rax E erg s gm 1 1 X

6 reaction rate r n n v # s 1 cm 3 ax a X r n n # s 1 cm 3 ax a X ax where ax ax cm s RDG

7 The Maxwellian Velocity Distribution P( )d 4 2 kt 3/ kT e d rms 3kT 7 RDG

8 V(r) = Z az X e 2 r V(r) electrostatic (Coulomb Potential) V(r) = a e bma Xr (Yukawa Potential) r 8RDG 1

9 V(r) r 9 RDG

10 Tunneling Probability E E P( E) e c/ where E is the Gamov Energy 10 RDG c

11 Big Bang Nucleosynthesis 11 RDG

12 12RDG 1

13 Big Bang Nucleosynthesis 13RDG 1

14 The Sun 14RDG 1

15 ppi, ppii, and ppiii chains T 6 < RDG

16 16RDG 1

17 Solar Main Sequence Nucleosynthesis and Gyr Network simulations at 10 7 K RDG 1

18 Neutrino Experiments Radioactivity Cherenkov Radiation in water 18RDG 1

19 19RDG 1

20 The Pontecorvo method makes use of the neutrino capture reaction, n + 37 Cl 37 Ar + e -. The reaction produces the isotope argon-37 that decays back to chlorine-37 by the inverse of the capture process, with a half-life of 35 days. In my experiment, carbon tetrachloride served as the target material. After exposing a tank of this liquid to a neutrino source for a month or two, the radioactive argon-37 atoms produced by neutrino capture were removed and counted in a small Geiger counter. The neutrino capture cross-section is extremely small. Therefore, one must use a very large volume of carbon tetrachloride. To observe the argon- 37 decays, it was necessary to develop a miniature counter with a very low background counting rate. Raymond Davis 20RDG 1

21 21 RDG

22 Kamiokande and Super Kamiokande Cherenkov Radiation 50,000 Tons of water 11,146 photomultipliers 22RDG 1

23 Sudbury Neutrino Observatory Radioactivity Neutrons Cherenkov Radiation 23RDG 1

24 New Neutrino Physics Muons and Tauons are electron-like particles produced by high energy particle interactions (Cosmic Rays, accelerators) ν e, ν, ν are produced by particle decays ν e ν, ν e ν, ν ν. 24RDG 1

Main Injector Neutrino Oscillation Search (MINOS) Protons produced in the

Minnesota, they may change into tau neutrinos, or may stay as muon neutrinos.

25 Main Injector Neutrino Oscillation Search (MINOS) Protons produced in the Fermilab accelerator ring hit the target and produce pions. These decay into muon neutrinos. As these neutrinos travel from Fermilab in Chicago to the Soudan site in Minnesota, they may change into tau neutrinos, or may stay as muon neutrinos. The detector is made of interleaved steel and scintillator. The neutrinos interact in the steel and their products are detected by the scintillators. 25 RDG

26 The CNO Tricycle and High Temperature Branch Reactions CNO: 15 < T 6 < 200 Hot CNO: 200 < T 6 < 500 rp process: 500 < T 6 26RDG 1

27 The CNO Cycle 27RDG 1

28 CNO II Cycle 28RDG 1

29 OF Cycle 29RDG 1

30 The CNO Tricycle 30RDG 1

31 The CNO Tricycle 31RDG 1

32 Triple Alpha Burning Triple Alpha requires T 6 > RDG 1

33 Helium Burning T 6 > 100 = T 8 33RDG 1

34 Carbon Burning T 6 > RDG 1

35 Oxygen Burning T 6 > 1000 = T 9 35RDG 1

36 T 9 = 3 Silicon Burning 36RDG 1

37 Silicon Burning 37RDG 1

38 Silicon Burning T 9 = 3 38RDG 1

39 Binding Energy per Nucleon 39RDG 1

40 Binding Energy per Nucleon Fusion reactions to the right of the iron-nickel peak are endothermic (energy absorbing) at Stellar interior temperatures. Since these reactions produce no heat, the stellar core will cool and collapse. 40RDG 1

41 Nuclear Fission Spontaneous Fission Chain Reaction Neutron Induced Fission 41RDG 1

42 Slow Neutron Capture-Process (the S-process) Occurs at relatively low neutron density and intermediate temperature conditions in AGB stars. Under these conditions the rate of neutron capture is slow relative to the rate of radioactive - decay A stable isotope captures another neutron; but a radioactive isotope decays to its stable daughter before the next neutron is captured. Produces approximately half of the isotopes of the elements heavier than iron. 42RDG 1

43 Slow Neutron Capture-Process (the S-process) Occurs at relatively low neutron density and intermediate temperature conditions in Asymptotic Giant Branch (AGB) stars. Under these conditions the rate of neutron capture is slow relative to the rate of radioactive - decay A stable isotope captures another neutron; but a radioactive isotope decays to its stable daughter before the next neutron is captured. Produces approximately half of the isotopes of the elements heavier than iron in galactic chemical evolution. 43RDG 1

44 Slow Neutron Capture-Process (the S-process) Because of the relatively low neutron fluxes associated with the S-process (10 5 to neutrons cm -2 s -1 ), this process does not have the ability to produce any of the heavy radioactive isotopes such as thorium or uranium. An example of how the S-process works is the cycle that terminates the S-process: 44RDG 1

45 The Core of a Massive Star Prior to its Collapse 45RDG 1

46 Nuclear Fission Spontaneous Fission Chain Reaction Neutron Induced Fission 46RDG 1

47 The Core Collapse of a Massive Star 47RDG 1

48 Rapid Neutron Capture-Process (the R-process) The process entails a succession of rapid neuron captures on iron seed nuclei An extremely high neutron flux follows immediately after a core-collapse supernova explosion (10 22 neutrons cm -2 s -1 ) Under these conditions the rate of neutron capture is fast relative to the rate of radioactive - decay A stable isotope captures a neutron, and the next neutron is captured before a beta decay can occur Produces approximately half of the isotopes of the elements heavier than iron in galactic chemical evolution 48RDG 1

49 Rapid Neutron Capture (the r Process) The Cas A Supernova Remnant 49RDG 1

50 of the Elements Predicted paths of the R- and S-processes on the chart of nuclides. Shown are nuclei which are stable or so long lived that they naturally exist (black), unstable nuclei for which the mass is known (green) and unstable nuclei that are predicted by nuclear theory to exist (yellow). 50RDG 1

MAJOR NUCLEAR BURNING STAGES

MAJOR NUCLEAR BURNING STAGES The Coulomb barrier is higher for heavier nuclei with high charge: The first reactions to occur are those involving light nuclei -- Starting from hydrogen burning, helium burning