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R-Process: Observations, Theory, Experiment

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R-Process: Observations, Theory, Experiment r-process: observations, theory, experiment H. Schatz Michigan State University National Superconducting Cyclotron Laboratory Joint Institute for Nuclear Astrophysics 1. Observations: do we need s,r,p-process and LEPP? 2. r-process (and LEPP?) models 3. r-process experiments SNR 0103-72.6 Credit: NASA/CXC/PSU/S.Park et al. Origin of the heavy elements in the solar system s-process: secondary • nuclei can be studied Æ reliable calculations • site identified • understood? Not quite … r-process: primary • most nuclei out of reach • site unknown p-process: secondary (except for νp-process) Æ Look for metal poor`stars (Pagel, Fig 6.8) To learn about the r-process Heavy elements in Metal Poor Halo Stars CS22892-052 (Sneden et al. 2003, Cowan) 2 1 + solar r CS 22892-052 ) H / X CS22892-052 ( g o red (K) giant oldl stars - formed before e located in halo Galaxyc was mixed n distance: 4.7 kpc theya preserve local d mass ~0.8 M_sol n pollutionu from individual b [Fe/H]= −3.0 nucleosynthesisa events [Dy/Fe]= +1.7 recall: element number[X/Y]=log(X/Y)-log(X/Y)solar What does it mean: for heavy r-process? For light r-process? • stellar abundances show r-process • process is not universal • process is universal • or second process exists (not visible in this star) Conclusions depend on s-process Look at residuals: Star – solar r Solar – s-process – p-process s-processSimmerer from Simmerer (Cowan et etal.) al. /Lodders (Cowan et al.) s-processTravaglio/Lodders from Travaglio et al. -0.50 -0.50 -1.00 -1.00 -1.50 -1.50 log e log e -2.00 -2.00 -2.50 -2.50 30 40 50 60 70 80 90 30 40 50 60 70 80 90 Element number Element number ÆÆNeedNeed reliable reliable s-process s-process (models (models and and nu nuclearclear data, data, incl. incl. weak weak s-process) s-process) ÆÆClearlyClearly something something is is going going on on for for Z Z < < ~50 ~50 (“light” (“light” p-process p-process elements) elements) Need to look at many stars … Look at many stars – consistent pattern? CS22892-052 HD 115444 For highly r-process BD+1703248 enriched stars CS 31082-001 Æ Very consistent pattern throughout except for U,Th HD221170 in CS 31082-001 Cowan et al. NIC9 proceedings Find more such stars ? • Only 1:1.2 Mio halo stars r-process element enhanced • Ongoing Surveys (e.g. SEGUE at Apache Point) might find 1000s of stars in relevant metallicity range What about less enriched stars? Montes et al. to be published Light r / Heavy r (Eu) Heavy r / Heavy r (Eu) Slope indicates ratio of light/heavy changes for less enriched stars Solar r Some stars have [La/Eu] light r-elements [Y/Eu] at solar level Light r-elements at high enrichment fairly robust and Heay r-pattern [Ag/Eu] [Sm/Eu] subsolar – part of robust and main r-process(?) agrees with [Eu/Fe] [Eu/Fe] solar – main Enrichment with main r-process r-process ÆConsistent with second process producing also Sr-Ag LEPP, identified by Travaglio et al. 2004 Honda et al. 2006 Ivans et al. 2006 Why –1 slope ? recall: [X/Y]=log(X/Y) - log(X/Y)solar [Y/Eu] = [Y/Fe] + [Fe/Eu] = [Y/Fe] – [Eu/Fe] Const (e.g. as a function of [Fe/H] ÆÆPrimaryPrimary process process makes makes Y Y ÆÆmademade with with Fe? Fe? The LEPP pattern? LEPP = HD122563 – (small) main r (black data points) LEPP = solar – s-process – main r (red data points) ÆÆLEPPLEPP produces produces a a consistent consistent pattern pattern ÆÆItIt contributes contributes to to solar solar abundances abundances (Montes et al. 20007 to be published, see also Qian&Wasserburg 2007) The r-process Temperature: ~1-2 GK Density: ~300 g/cm3 (~60% neutrons !) neutron capture timescale: ~ ms - μs Rapid neutron capture β-decay Seed r e b Equilibrium favors m u n “waiting point” (γ,n) photodisintegration n o t o r P Neutron number Pt Xe Ni 78Ni, 79Cu first bottle necks in n-capture flow (80Zn later) 79Cu: half-life measured 188 ms (Kratz et al, 1991) 78Ni : half-life predicted 130 – 480 ms 2 events @ GSI (Bernas et al. 1997) r-process in Supernovae ? Most favored scenario for high entropy: Neutrino heated wind evaporating from proto neutron star in core collapse + νe neutrino sphere (νe+p Æ n+e weak opacity because only few protons present) - νe neutrino sphere (ve+n Æ p+e strong opacity because many neutrons present) proto neutron star weak interactions regulate n/p ratio: + (n-rich) νe+p Æ n+e faster as νe come from deeper - and are therefore hotter ! νe+n Æ p+e therefore matter is driven neutron rich How does the r-process work ? Neutron capture ! Recent calculation Martinez-Pinedo et al. 2006 (NIC proceedings) MainMain problem: problem: conditions conditions needed needed for for full fullr-processr-process not not achieved achieved ••acousticacoustic mechanism? mechanism? (Arizona (Arizona group) group) •• reverse reverse shock shock (interaction (interaction of of fast fast wind wind with with slow slow main main ejecta)(Munich ejecta)(Munich group) group) •• OR OR don’t don’t need need ν ν-wind-wind for for full full r-process r-process – – look look for for other other scenarios? scenarios? What about LEPP? Trying to fit with n-capture flow Low nn High nn Æ Low nn and high nn fit low Z but not high Z multi-component? A=130 overproduction! Æ Low nn also fits small high Z abundances ??? Why nuclear physics I - Sensitivity of abundances Sensitivity to astrophysics Sensitivity to nuclear physics 1 10 Hot bubble ETFSI-Q masses Classical model ETFSI-1 masses Same nuclear physics 0 Same r-process model 10 -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 ~ T1/2(prog), • freezeout key waiting points set timescale) • neutrino presence • n-capture rates • which model is correct • fission barriers and fragments Why nuclear physics II: disentangling LEPP and main-r Remember before: r-process = solar – s-process needed accurate s-process Isotopic: • s-process models (with solar s-only) • s-process data LEPP = Solar – s-process – main-r (– p-process) Elemental: Isotopic: • rII halo star abundances Reliable solar abundances Isotopic: • main r-process model • r-process data A=80-110 Becomes now possible ÆÆNowNow progress progress on on all all pieces pieces of of the the puzzle puzzle possible possible H. Schatz Nuclear physics in the r-process Fission rates and distributions: • n-induced • spontaneous β-delayed n-emission • β-delayed branchings (final abundances) β-decay half-lives (abundances and process speed) n-capture rates • in slow freezeout • maybe in a “weak” r-process ? ν-physics ? Seed production rates (ααα,ααn, α2n, ..) Masses (Sn) (location of the path) H. Schatz Some recent r-process motivated experiments ANL/CPT (Cf source) Remeasured masses with high precision ORNL (ISOL) (d,p) and Coulex GSI (in-flight fission) Masses (IMS) (Matos & Scheidenberger et al.) GSI (in-flight fission) ISOLTRAP masses Half-lives, Pn values (Santi, Stolz et al., Kurtukian-Nieto et al.) MSU/NSCL TOF masses ISOLDE (ISOL) (Matos, Estrade et al.) Decay spectroscopy (Dillmann et al. 2003) MSU/NSCL (fragmentation) Half-lives, Pn values (Hosmer, Santi, Montes, Pereira Hennrich, Quinn, et al.) GANIL (fragmentation) Decay spectroscopy, Sorlin et al. Coupled Cyclotron Facility since 2001 r-process beams at the NSCL Coupled Cyclotron Facility 86 136 86Kr,Kr, 136XeXe beam beam r-process ~140~140 MeV/u MeV/u beam TOF dE Be target Tracking Be target (=rigidity Bρ) AdvantagesAdvantages of of fast fast RIB RIB from from fragmentation: fragmentation: •• no no decay decay losses losses •• any any beam beam can can be be produced produced •• multiple multiple measurements measurements in in one one •• high high sensitivity sensitivity Particle Identification Z) Æ r-process nuclei 78 78NiNi DoublyDoubly Energy loss in Si ( MagicMagic ! ! 78Ni 77Ni 75Co 74Co 73Co Time of flight (Æ m/q – corrected for Bρ) Particle ID (Pereira, Hennrich, et al.) (corrected for momentum Preliminary dependence) r-process 111 Energy loss Mo 107Zr 105Y velocity Setup Measure:Measure: ••ββ-decay-decay half-lives half-lives •• Branchings Branchings for for β β-delayed-delayed n-emission n-emission Detect:Detect: • Particle type (TOF, dE, p) New NSCL Neutron detector • Particle type (TOF, dE, p) NERO •• Implantation Implantation time time and and location location ••ββ-emission-emission time time and and location location 3He + n -> t + p •neutron-•neutron-ββcoincidencescoincidences neutron Fast Fragment Beam Si Stack (fragment. 140 MeV/u 86Kr) NERO – Neutron Emission Ratio Observer 3He Proportional BF3 Proportional Counters Counters Specifications: • 60 counters total 3 (16 He , 44 BF3) • 60 cm x 60 cm x 80 cm polyethylene block • Extensive exterior shielding • 43% total neutron efficiency (MCNP) Polyethylene Boron Carbide Moderator Shielding NERO Assembly Nero efficiency NERO Efficiency vs. Neutron Energy 50 13C 40 11B 30 20 51V Efficiency (%) 10 252Cf 0 0.001 0.01 0.1 1 10 Scaled MCNP Curve Neutron Energy (MeV) Decay curves Decay-curves fits (mother, daughter, granddaughter) 106 107 105Zr Zr Zr Branchings for neutron emission (Pn) from counting β-n coincidences β− Pn probes strength near gs and near Sn (Z,A) Æ First constraint on strength distribution n Sn (Z+1,A-1) γ (Z+1,A) Results from earlier experiment in Ni-Cu region H. Schatz Impact of 78Ni half-life on r-process models Observed Solar Abundances 1.E+021.E+02 Model Calculation: Half-Lives from Moeller, et al.
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