(from Rene Reifarth) ss the s-process s-only Zr

(from Rene Reifarth) ss the s-process s-only Zr

(from Rene Reifarth) ss the s-process s-only Zr Y Ni Co Fe rpr oc e ss proton number

ppr oc e Br, t1/2=17 min, 92 % (), 8 % () Sr (n,) Rb p-only Kr Br () Se 85 As () Kr, t1/2=11 a Ge 79 Se, t1/2=65 ka Ga Zn

r-only Cu 80 Cu, t1/2=12 h, 40 % (), 60 % () 63 Ni,neutron t1/2=100number a 64 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 Y Y ( n , ) const can easily interpolate s-contribution for s+r-nuclei if neutron capture cross

sections are known The weak s-process Site: Core He burning (and shell C-burning) in massive stars (e.g. 25 solar masses) 14 N is rapidly converted to 22Ne 22Ne 18O He burning core contains initially 14N capture capture 18O 14N

Towards the end of He burning T~3e8 K: 22Ne(,n) n) provides a neutron source preexisting Fe (and other nuclei) serve as seed for a (secondary) s-process Typical conditions (Raiteri et al. ApJ367 (1991) 228 and ApJ371(1991)665: Temperature 2.2 - 3.5 e8 K Density 1 - 3e3 g/cm3 Average neutron density 7e5 cm-3 Peak neutron density 2e7 cm-3 Neutron exposure

0.206 / mb ) time integrated neutron flux * produced abundance/solar Results: jn (t )dt 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) 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 burning shell s-process in: He flash via 22Ne(,n) n) He flash (thermal pulse) 13C pocket 40 yr (Lugaro et al. ApJ586(2003)1305) 160 yr

52,n) 000 yr 13C pocket via 13C(,n) n) Conditions during the main s-process 13 C(,n) in pocket 22 Ne(,n) in He flash Temperature 0.9 x 108 K 2.7 x 108 K Neutron density

7 x 107 cm-3 1010 cm-3 Duration 20,000 yr few years Neutron exposure 0.1 / mb 0.01 / mb weaker but longer main contribution (90% of exposure) short, intense burst slight modification of abundances

(branchings !) Results for main s-process model = s-only (Arlandini et al. ApJ525 (1999) 886) 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) p-process mechanism Secondary process. Seed: previous s-process in low mass star) Series of (,n) (,p) (,) photodisintegration reactions (also called -process)

produced by disintegration of heavier nuclei (,n) (,p) produces eventually lighter p-nuclei (,n) (,n) p nucleus (,n) s nucleus p-process path Rayet et al. A&A227(1990)271

p-nuclei (,n) flow stopped by (n,) flow proceeds via (,p) or (,) p-process model results Mo-Ru underproduction problem (1-10% isotopic fraction !) (Rayet et al. A&A298 (1995) 517)

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