1/15 The r-Process in the High- Entropy-Wind of Type II SNe K. Farouqi Inst. für Kernchemie Univ. Mainz, Germany Frontiers Workshop August
2/15 The High-Entropy-Wind Site r-process
3/15 For a given blob of matter behind the shock front above the proto-neutron star : define three parameters: Electron abundance: Y e =Y p =1-Y n (p/n-ratio) Example: Y e =0.45 55% neutrons & 45% protons Radiation entropy: S rad ~ T 3 /ρ ( n n ) Expansion speed V exp which determines the process durations and r : Example: V exp = 7500 km/s, R 0 = 130 km = 35 ms, r = 280 ms
4/15 The -process NSE: All nuclear reactions via strong and electro-magnetic interactions are very fast when compared with dynamical timescales. At T 9 ≈ 6, -particles become the dominant constituent of the hot bubble! Recombination of the -particles is possible via: 1.3 → 12 C and 2. + +n → 9 Be, followed by 9 Be( ,n) 12 C Charged-particle freeze-out at T 9 ≈ 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.
5/15 Seed nuclei after an -rich freeze-out S=200, V exp =7500 km/s Neutron-rich seed beyond N=50 difference to „classical“ r-process with 56 Fe seed avoids N=50 r-process bottle-neck seed nuclei: 94 Kr, 100 Sr ( 87 Se, 103 Y, 89 Br, 84 Ge, 95 Kr, 76 Ni, 95 Rb below 5%)
6/15 Parameter combinations allowing a subsequent r-process r-process „strength“ formula: (1<Y n /Y seed <150)
7/15 Synthesizing the A=130 peak S=196 Process duration: 146 ms YeYe Entropy S r-processduration [ms] n n [cm -3 ] at freeze-out T 9 [10 9 K] at freeze-out 0, ,9 x ,53 0, ,1 x ,79 0, ,0 x ,77
8/15 S=261 Pb Th U not yet enough Process duration: 327 ms YeYe Entropy S r-processduration [ms] n n [cm -3 ] at freeze-out T 9 [10 9 K] at freeze-out 0, ,0 x ,33 0, ,5 x , ,9 x ,42 Synthesizing the A=195 peak
9/15 Synthesizing the Th, U region S=280 Pb Th U Process duration: 463 ms
10/15 Synthesizing the A=130 and A=195 peaks plus the Th, U region S= Superposition of individual S-components Pb Th U
11/15 Superposition of 6 entropy sequences to reproduce the total solar r-process pattern (70< A <240) A=130 (N=82) shell A=195 (N=126) shell Th, U r-process chronometers 14 Gyr
12/15 Abundance 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 up to the A≈130 peak region ! However, for A>140 (REE,third peak, Th-U) S>250 components freeze-out slower ↷ late neutron capture can modify the final r-abundance pattern Y e = 0.45 S = 195
13/15 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“ abundances blue: β-delayed neutrons emitted and re-captured
14/15 Summary Conditions for successfull r-process (even for Y e =0.49!) „strength“ formula Y n /Y seed =f(S,Y e,V exp ) Due to improved nunclear-physics input max. S=280 (for Y e =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
15/15 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.