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The Origin of Heavy Elements in the Solar System

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The Origin of Heavy Elements in the Solar System The origin of heavy elements in the solar system (Pagel, Fig 6.8) each process contribution is a mix of many events ! 1 Abundance pattern: “Finger print ” of the r-process ? Tellurium and Xenon Peak Platinum Peak Solar abundance of the elements r-process only (subtract s,p processes) ) 6 Abundance (Si(Si = =Abundance Abundance 10 10 Element number (Z) But: sun formed ~10 billion years after big bang: many stars contributed to elements This could be an accidental combination of many different “fingerprints ” ? Find a star that is much older than the sun to find “fingerprint ” of single event 2 Heavy elements in Metal Poor Halo Stars CS22892-052 red (K) giant located in halo distance: 4.7 kpc mass ~0.8 M_sol [Fe/H]= −−−3.0 recall: [Dy/Fe]= +1.7 [X/Y]=log(X/Y)-log(X/Y) solar old stars - formed before Galaxy was mixed they preserve local pollution from individual nucleosynthesis events 3 A single (or a few) r -process event(s) CS22892-052 (Sneden et al. 2003) 1 solar r Cosmo Chronometer 0 -1 NEW: CS31082-001 with U (Cayrel et al. 2001) -2 40 50 60 70 80 90 Age: 16+ - 3 Gyr element number (Schatz et al. 2002 other, second ApJ 579, 626) r-process to fill main r-process this up ? matches exactly solar r-pattern (weak r-process) conclusions ? 4 More rII stars Solar r-process elements from many events J. Cowan 5 A surprise J. Cowan A new process contributing to Y, Sr, Zr (early Galaxy only? Solar? In this case: some traditional “r-contributions” to solar are not (main) r-process) Call it LEPP (Light Element Primary Process) 6 Overview heavy element nucleosynthesis process conditions timescale site s-process T~ 0.1 GK 10 2 yr Massive stars (weak) τ 7- 5-6 (n-capture, ...) n~ 1-1000 yr, n n~10 and 10 yrs Low mass AGB stars (main) 8/cm 3 r-process T~1-2 GK < 1s Core collapse supernovae ? τ µ 24 3 (n-capture, ...) n ~ s, n n~10 /cm Neutron Star Mergers ? p-process T~2 -3 GK ~1s Core collapse supernovae ? (( γ,n), ...) Type Ia supernovae? Light Element ??? Primary Process (LEPP) ? Weak r-process? Failed r-process? νp-process? Primary s-process? 7 The r-process Temperature: ~1-2 GK Density: 300 g/cm3 (~60% neutrons !) neutron capture timescale: ~ 0.2 µs Rapid neutron capture βββ-decay Seed Equilibrium favors (γγγ,n) photodisintegration “““waiting point ””” Neutron number 8 Waiting point approximation Definition: ASSUME (n, γ)-(γ,n) equilibrium within isotopic chain How good is the approximation ? This is a valid assumption during most of the r-process BUT: freezeout is neglected Freiburghaus et al. ApJ 516 (2999) 381 showed agreement with dynamical models Consequences During (n, γ)-(γ,n) equilibrium abundances within an isotopic chain are given by: 2/3 + + + πh2 Y (Z, A 1) = G(Z, A 1) A 1 2 nn exp( Sn / kT ) Y (Z, A) 2G(Z, A) A mu kT • time independent • can treat whole chain as a single nucleus in network • only slow beta decays need to be calculated dynamically • neutron capture rate independent (therefore: during most of the r-process n-capture rates do not matter !) 9 Waiting point approximation continued In the approximation of continuous Sn and abundances Y the maximum abundance in an isotopic chain occurs for Y(Z, A +1) =1 Y(Z, A) For a given temperature and neutron density one can solve for Sn (assuming A~A+1 and G=1) 3/2 2 m kT S = kT ln u n πh2 nn 2 T 3 S = 9 ln(T )− ln(n )+ 78.460 in MeV n 11.6042 9 n r-process runs at fixed neutron separation energy (for given condition) 10 11 H. Schatz Nuclear physics in the r-process Fission rates and distributions: • n-induced • spontaneous βββ-delayed n-emission • βββ-delayed branchings (final abundances) βββ-decay half -lives (abundances and process speed) n-capture rates • in slow freezeout • maybe in a “weak ” r-process ? ννν-phyiscs ? Seed production rates ( ααα ,αααααα n, ααα2n, ..) Masses (Sn) (location of the path) 12 Sensitivity of r-process to astro and nuclear physics Sensitivity to astrophysics Sensitivity to nuclear physics 1 10 Hot bubble ETFSI-Q masses Classical model ETFSI-1 masses Same nuclear physics 0 10 Same r-process model -1 10 -2 10 Abundance -3 10 Freiburghaus et al. 1999 -4 10 100 120 140 160 180 200 220 Mass number Mass number Contains information about: But convoluted with nuclear physics: • n-density, T, time • masses (set path) (fission signatures) •T1/2 , Pn (Y ~ T 1/2(prog) , • freezeout key waiting points set timescale) • neutrino presence • n-capture rates • which model is correct • fission barriers and fragments 13 Shell quenching effect on masses/r-process Ru Pd Cd Mo Zr r-process path S2n (MeV) (MeV) S2n S2n ETFSI-1 Neutron number 14 Shell quenching effect on masses/r-process Ru Pd Cd Mo Zr distinguish S2n (MeV) (MeV) S2n S2n ETFSI-1 ETFSI-Q (N=82 quenched) Neutron number 15 Endpoint of the r-process r-process ended by n-induced fission or spontaneous fission (different paths for different conditions) (Goriely & Clerbaux A&A 348 (1999), 798 n-induced fission β-delayed fission spontaneous fission n-capture (DC) β− (Z,A) (Z,A) fission fission fission (Z,A+1) fission barrier (Z,A+1) (Z+1,A) 16 Consequences of fission Fission produces A~A end /2 ~ 125 nuclei modification of abundances around A=130 peak fission products can serve as seed for the r-process - are processed again into A~250 region via r-process - fission again fission cycling ! Note: the exact endpoint of the r-process and the degree and impact of fission are unknown because: • Site conditions not known – is n/seed ratio large enough to reach fission ? (or even large enough for fission cycling ?) • Fission barriers highly uncertain • Fission fragment distributions not reliably calculated so far (for fission from excited states !) 17 Role of beta delayed neutron emission β Neutron rich nuclei can emit one or more neutrons during -decay if Sn<Q βββ (the more neutron rich, the lower S n and the higher Q β) βββ−−− (Z,A) n Sn (Z+1,A-1) γγγ (Z+1,A) If some fraction of decay goes above S n in daughter nucleus - ν)ν)ν) then some fraction Pn of the decays will emit a neutron (in addition to e and (generally, neutron emission competes favorably with γ-decay - strong interaction !) 18 Effects: during r-process : none as neutrons get recaptured quickly during freezeout • modification: of final abundance • late time neutron production (those get recaptured) Calculated r-process production of elements (Kratz et al. ApJ 403 (1993) 216): before β-decay after β-decay smoothing effect from βββ-delayed n emission ! 19 Cs (55) Cs131 Cs132 Cs133 Cs134 Cs135 Cs136 Cs137 Cs138 Cs139 Cs140 Cs141 Cs142 Cs143 Cs144 Cs145 Cs146 Cs147 > 99 > 99 > 99 19.00 > 99 > 99 > 99 63.70 24.94 1.70 1.78 1.01 0.59 0.32 0.23 Xe130 Xe131 Xe132 Xe133 Xe134 Xe135 Xe136 Xe137 Xe138 Xe139 Xe140 Xe141 Xe142 Xe143 Xe144 Xe145 Xe146 Xe (54) r-process > 99 > 99 > 99 > 99Pn39.68=0% 13.60 1.73 1.24 0.30 1.15 0.90 I129 I130 I131 I132 I133 I134 I135 I136 I137 I138 I139 I140 I141 I142 I143 I144 I145 I (53) waiting point > 99 > 99 > 99 > 99 > 99 > 99 83.40 24.50 6.49 2.28 0.86 0.43 Te (52) Te128 Te129 Te130 Te131 Te132 Te133 Te134 Te135 Te136 Te137 Te138 Te139 Te140 Te141 Te142 Te143 Te144 > 99 > 99 > 99 > 99 > 99 19.00 17.50 2.49 1.40 P =99.9% Sb (51) Sb127 Sb128 Sb129 Sb130 Sb131 Sb132 Sb133n Sb134 Sb135 Sb136 Sb137 Sb138 Sb139 Sb140 Sb141 Sb142 Sb143 > 99 > 99 > 99 > 99 > 99 > 99 > 99 1.66 0.82 Sn (50) Sn126 Sn127 Sn128 Sn129 Sn130 Sn131 Sn132 Sn133 Sn134 Sn135 Sn136 Sn137 Sn138 Sn139 Sn140 Sn141 Sn142 > 99 > 99 > 99 > 99 > 99 56.00 39.70 1.20 1.12 In (49) In125 In126 In127 In128 In129 In130 In131 In132 In133 In134 In135 In136 In137 In138 In139 In140 In141 2.36 1.60 1.09 0.84 0.61 0.26 0.28 0.20 0.18 137 1 Example: impact of P n for Sb Cd (48) Cd124 Cd125 Cd126 Cd127 Cd128 Cd129 Cd130 Cd131 Cd13210 Cd133 Cd134 Cd135 Cd136 Cd138 Cd139 Cd140 1.24 0.65 0.51 0.43 0.34 0.27 0.20 A=136 A=137 Ag123 Ag124 Ag125 Ag126 Ag127 Ag128 Ag129 Ag130 Ag131 Ag132 Ag133 Ag135 Ag136 Ag137 Ag138 Ag139 Ag (47) ( 99%) ( 0%) 0.29 0.17 0.16 0.10 0.11 0.06 0.05 Si) 6 76 77 78 79 80 81 82 83 1084 0 85 86 87 88 89 90 91 92 r-process waiting point 10 -1 Pn=0% solar abundance (per 10 abundance (per Pn=99% 10 -2 125 130 135 140 145 mass number A 20 Summary: Nuclear physics in the r-process Quantity Effect Sn neutron separation path energy βββ T1/2 -decay half-lives • abundance pattern • timescale βββ Pn -delayed n-emission final abundance pattern branchings fission (branchings • endpoint and products) • abundance pattern? • degree of fission cycling G partition functions • path (very weakly) σσσ NA< v> neutron capture rates • final abundance pattern during freezeout ? • conditions for waiting point approximation 21 National Superconducting Cyclotron Laboratory at Michigan State University New Coupled Cyclotron Facility – experiments since mid 2001 Ion Source: 86 Kr beam 86 Kr beam 140 MeV/u Tracking TOF start 86 Implant beam Kr hits Be (=Momentum) target and in detector and observe decay fragments Separated beam TOF stop of r-process dE detector nuclei Fast beam fragmentation facility – allows event by event particle identification 22 Fragment yield after Br selection Fragment yield after Br selection First r-process experiments at new NSCL CCF facility (June 02) Measure: • β-decay half-lives • Branchings for β-delayed n-emission Detect: • Particle type (TOF, dE, p) New NSCL Neutron detector • Implantation time and location NERO β • -emission time and location 3He + n -> t + p • neutron-β coincidences neutron Fast Fragment Beam Si Stack (fragment.
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