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The r-Process in the High-Entropy-Wind of Type II SNe

K. FarouqiInst. für Kernchemie Univ. Mainz, Germany

Frontiers Workshop

August 20-22 2005

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The High-Entropy-Wind Site

r-process

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For a given blob of matter behind the shock front above the proto-neutron star :

define three parameters:

• Electron abundance: Ye=Yp=1-Yn (p/n-ratio)

Example: Ye=0.45 55% neutrons & 45% protons

• Radiation entropy: Srad ~ T3/ρ ( nn)

• Expansion speed Vexp which determines the process durations and r :

Example: Vexp= 7500 km/s, R0= 130 km = 35 ms, r= 280 ms

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The -process • NSE: All nuclear reactions via strong and electro-magnetic

interactions are very fast when compared with dynamical timescales.

At T9 ≈ 6, -particles become the dominant constituent of the hot bubble!

Recombination of the -particles is possible via:

1. 3→ 12C and2. ++n → 9Be, followed by 9Be(,n) 12C

• Charged-particle freeze-out at T9 ≈ 3 with:

– Dominant part of -particles ~ 80%

– Some heavy nuclei beyond iron (80 <A< 110)

– Probably a little bit of free neutrons

Seed composition for a subsequent r-process.

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Seed nuclei after an -rich freeze-out

S=200, Vexp=7500 km/s

Neutron-rich seed beyond N=50 difference to „classical“ r-process with 56Fe seed

avoids N=50 r-process bottle-neck seed nuclei: 94Kr, 100Sr (87Se, 103Y, 89Br, 84Ge, 95Kr, 76Ni, 95Rb below 5%)

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Parameter combinations allowing a subsequent r-process

r-process „strength“ formula:

(1<Yn/Yseed<150)

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Synthesizing the A=130 peakS=196

Process duration: 146 ms

Ye Entropy S r-processduration

[ms]nn [cm-3]

at freeze-out

T9 [109 K]

at freeze-out0,49 230 234 1,9 x1020 0,53

0,45 190 146 8,1 x1021 0,79

0,41 160 109 9,0 x1021 0,77

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S=261

Pb

Th

U

not yet enough Process duration: 327 ms

Ye Entropy S r-processduration

[ms]nn [cm-3]

at freeze-out

T9 [109 K]

at freeze-out

0,49 290 412 2,0 x1021 0,33

0,45 260 327 1,5 x1022 0,41

0,41 235 213 2,9 x1022 0,42

Synthesizing the A=195 peak

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Synthesizing the Th, U region

S=280

Pb

ThU

Process duration: 463 ms

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Synthesizing the A=130 and A=195 peaks plus the Th, U region

S=196 + 261 + 280

Superposition of individual S-components

Pb

Th

U

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Superposition of 6 entropy sequences to reproduce thetotal solar r-process pattern (70< A <240)

A=130(N=82) shell

A=195(N=126) shell

Th, U

r-processchronometers

14 Gyr

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Abu

ndan

ce Y

Massnumber

Neuton capture rates

temperature-dependent <> from NON-SMOKER (T. Rauscher)

Dynamic r-process network calculations for the high-entropy wind scenario of SNII

Due to still “fast“ freeze-out, no significant effect of <> upto the A≈130 peak region !

However, for A>140 (REE,third peak, Th-U)

S>250 componentsfreeze-out slower

↷ late neutron capture can modify the final r-abundance

pattern

Ye= 0.45S = 195

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The role of β-delayed neutrons in the r-process at A=130 and 195

red: no re-captured β-delayed neutrons

blue: β-delayed neutrons re-captured

red: no β-delayed neutrons emitted „progenitor“ abundancesblue: β-delayed neutrons emitted and re-captured

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Summary

• Conditions for successfull r-process (even for Ye=0.49!) „strength“ formula Yn/Yseed=f(S,Ye,Vexp) • Due to improved nunclear-physics input max. S=280 (for Ye=0.45)

• Total process duration up to Th, U r=465 ms leaves time for fission recycling

• Freeze-out effects (late non-equilibrium phase) negligible up to A=130 peak important for REE „pygmy“ peak and A=195 peak

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Outlook

• Needed : - more experimental nuclear-physics data - better global theoretical models for: nuclear masses, gross -decay properties neutron-capture rates,fission properties,…. • Neutrino effects

• Inclusion of r-process network into 3D hydro-dynamical SN simulations.