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the s-process

80 Br, t 1/2 =17 min, 92 % ( b - ) , 8 % ( b + ). p-p r ocess. proton number. 85 Kr, t 1/2 =11 a. 79 Se, t 1/2 =65 ka. r-process. 64 Cu, t 1/2 =12 h, 40 % ( b - ) , 60 % ( b + ). 63 Ni, t 1/2 =100 a. neutron number. s-only. (from Rene Reifarth). the s-process. Zr. Y. Sr. (n, g ).

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the s-process

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  1. 80Br, t1/2=17 min, 92 % (b-),8 % (b+) p-process proton number 85Kr, t1/2=11 a 79Se, t1/2=65 ka r-process 64Cu, t1/2=12 h, 40 % (b-),60 % (b+) 63Ni, t1/2=100 a neutron number s-only (from Rene Reifarth) the s-process Zr Y Sr (n,g) Rb p-only Kr Br (b-) Se As (b+) Ge Ga Zn r-only Cu Ni Co Fe

  2. The sites of the s-process weak s-process: core He/ shell C burning in massive stars main s-process: He shell flashes in low mass TP-AGB stars approx. steady flow can easily interpolates-contribution for s+r-nucleiif neutron capture crosssections are known

  3. The weak s-process Site: Core He burning (and shell C-burning) in massive stars (e.g. 25 solar masses) 14N is rapidly converted to 22Ne 22Ne He burning corecontainsinitially 14N a capture 18O b+ a capture 18O 14N Towards the end of He burning T~3e8 K: 22Ne(a,n) provides a neutron source preexisting Fe (and other nuclei) serve as seed for a (secondary) s-process

  4. Typical conditions (Raiteri et al. ApJ367 (1991) 228 and ApJ371(1991)665: *) time integrated neutron flux Results: produced abundance/solar

  5. The main s-process Site: low mass TP-AGB stars ( thermally pulsing stars on the asymptotic giant branch in the HR diagram, 1.5 - 3 solar masses ) H-burning shell CO core He-burning shell unstable - burns in flashes(thin shell instability)

  6. H/He burning in a TP-AGB star • number of He flashes in stars life: few – 100 • period of flashes: 1000 – 100,000 years H burningshell s-process in: • He flash via 22Ne(a,n) He flash(thermalpulse) 13C pocket • 13C pocket via 13C(a,n) 40 yr 160 yr 52,000 yr (Lugaro et al. ApJ586(2003)1305)

  7. Conditions during the main s-process short, intense burstslight modificationof abundances(branchings !) weaker but longermain contribution(90% of exposure)

  8. Results for main s-process model = s-only (Arlandini et al. ApJ525 (1999) 886)

  9. The p-process • produces p-rich, usually rare (0.1-1% isotopic fraction), stable isotopes • Site: Supernova shock passing through O-Ne layers of progenitor star Conditions at different locations in O/Ne layers during a Supernova: (Rayet et al. A&A298 (1995) 517)

  10. p-process mechanism Secondary process. Seed: previous s-process in low mass star) • Series of • (g,n) • (g,p) • (g,a)photodisintegration reactions (also called g-process) produced by disintegrationof heavier nuclei (g,n) (g,n) (g,n) pnucleus (g,n) snucleus (g,p) produces eventuallylighter p-nuclei

  11. p-process pathRayet et al. A&A227(1990)271 p-nuclei (g,n) flow stopped by (n,g) flow proceeds via (g,p) or (g,a)

  12. p-process model results Mo-Ruunderproductionproblem (1-10%isotopic fraction !) (Rayet et al. A&A298 (1995) 517)

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