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r-Process Nucleosynthesis – from Burr Oak to Present

r-Process Nucleosynthesis – from Burr Oak to Present. T 1/2. s n g. S n. P n. . Karl-Ludwig Kratz. Max-Planck-Institut für Chemie, Mainz, Germany Department of Physics, Univ. of Notre Dame, USA. CLAUS 2009. Historical introduction (I).

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r-Process Nucleosynthesis – from Burr Oak to Present

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  1. r-Process Nucleosynthesis – from Burr Oak to Present T1/2 sng Sn Pn  Karl-Ludwig Kratz • Max-Planck-Institut für Chemie, Mainz, Germany • Department of Physics, Univ. of Notre Dame, USA CLAUS 2009

  2. Historical introduction (I)                    Because of the important contribution of halogen isotopes                   to the ß-delayed neutron groups occuring in fission,                   rapid chemical separation procedures for bromine (Br) and iodine (I)                   were already developed in the 1950's by several groups.                   In those days, chemical ELEMENT separation was (still) superior to                   physical MASS separation.                   Halogen isotopes with half-lives down to a few seconds were identified,                   the shortest ones being1.6 s  90Br    and    2.0 s  139I Z separation of N eutron-rich I sotopes by A utomated M ethods To proceed to even shorter-lived nuclides, ultra-fast separation methods have been worked out in the late 1960's and early 1970's mainly at Kernchemie.

  3. Historical introduction (II)               This was also the subject of my PhD thesis, in which I worked out a procedure               based upon the formation of methyl-halides in a hot-atom reaction between               fission halogens recoiling from a solid U-235 target into gaseous methane:Br* / I*  +  CH4  ====>  CH3Br* / I*  + H° ... published in:                         RADIOCHEM. RADIOANAL. LETTERS 13 /5-6/ 385 -390 /1973/RAPID SEPARATION OF FISSION HALOGENS BY RECOIL REACTIONS                                                             WITH METHANE                                                     K.-L. Kratz, G. Herrmann                            Institut für Kernchemie, Universität Mainz, D-65 Mainz, G.F.R. ... shortest-lived NEW isotopes detected :0.65 s  91Br,  0.25 s  92Br    and    0.45 s  141I,  ~0.2 s  142I

  4. Historical introduction (III) Schematical diagram of the experimental setup,installed at a rapid pneumatic tube system of the Mainz TRIGA reactor Time sequence:0  s           Pulse irradiation; rabbit is projected out of reactor0.12 s       Rabbit is flushed by methane (~30 l/min) via path 10.4 s         Absorption traps are flushed by methane via path 20.50 s       Traps are projected to the detector positions0.60 s       Measurement (ßdn's or γ's) is started

  5. Histortical introduction (IV) Since Kernchemie Mainz was world-leading in rapid chemical separations,         and just had started to work on physical mass separation at                          OSTIS (ILL)  and  ISOLDE (CERN) ...in 1981, I got an invitation by    CLAUS  ROLFS              to a USA -- European workshop on "Nuclear Astrophysics“ at    B u r r  O a kThe suggested title of my talk:"Beta-decay detection METHODS and LIMITS"This workshop became my major scientific turning-point....

  6. Historical introduction (V) ... what was the actual reason to become interested in"Nuclear Astrophysics" ?           it was a talk by Willy Fowler on the isotopic FUN anomalies of Ca and Ti                            found in the EK-1-4-1 inclusion of the Allende meteorite ...in particular 48Ca/46Ca = 250!"...  Agreement for the 46C and 49Ti anomalies was obtained                              (within the assumed "nß"- nucleosynthesis process) by increasing the theoretical Hauser-Feshbach cross sections for 46K(n,γ) and 49Ca(n,γ) by a factor 10 on the basis of probable thermal (30 keV, s-wave) resonances  [....]  in the compound nuclei 47K and 50Ca, respectively. ..."                 -----------------------------------------------------------------------------------------Already during this talk I wondered,               if we had already measured this resonance at ISOLDE via high-resolutionß-delayed neutron spectrosopy of50K(ß-)50*Ca(n)49Ca                so to say as "inverse process" to neutron capture of                                                          8.7 min  49Ca(n,γ)50Ca ....

  7. The EK-1-4-1 story (I) … Requested low-lying s-wave resonance in 50Ca does exist; however, not at 30 keV, but at 155 keV. nß-processr-process

  8. The EK-1-4-1 story (II) This work N28 Ar, Cl, S, P at GANIL / LISE

  9. The EK-1-4-1 story (III) Updates: Experiments at CERN/ISOLDE & GANIL/LISE Theoretical n-capture rates (CN + DC) Astrophysical network calculations EK-1-4-1 Two astrophysical scenarios: (i) α-process (ii) weak r-process α-rich freezeout from Si-QSEFe-QSE + n-capt. SN Ia SN II EK-1-4-1 EK-1-4-1

  10. Fit of Nr, from B²FH Reproduction of Solar system isotopic r-process abundances • assumption (n,)(,n) equillibrium„waiting-point“concept • „static“ calculation • astrophysical conditions explosive He-burning in SN-I • T9 1 • nn 1024 cm-3 • r  10 – 100 s • neutron source:21Ne(,n) • nuclear physics: Q - Weizsäcker mass formula + empirical corrections (shell, deformation, pairing) • T1/2–one allowed transition to excited state, logft = 3.85

  11. 132Sn 50 (n,) 134 135 136 137 133 131 165ms Pn~85% 278ms (n,) 134 135 132 130 162ms 131 132 133 129 46ms(g) 158ms(m) 130 128 133In84 49 131In82 49 127 130Cd82 48 129Ag82 126 r-process path 47 (n,) 128Pd82 46 127Rh82 45 r-Abundance peaks and neutron-shell numbers „Try the impossible“ (C. Rolfs): measure the key waiting-point isotope 130Cd already B²FH (Revs. Mod. Phys. 29; 1957) C.D. Coryell (J. Chem. Educ. 38; 1961) b “climb up the staircase“ at N=82; major waiting point nuclei; “break-through pair“131In, 133In; K.-L. Kratz (Revs. Mod. Astr. 1; 1988) climb up the N= 82 ladder ... A  130 “bottle neck“ total r-process duration r “association with the rising side of major peaks in the abundance curve“ T1/2

  12. What we knew already in 1986 … Z. Phys. A325, 489 (1986) Exp. at old SC-ISOLDE with plasma ion-source quartz transfer line and dn counting Problems: high background from -surface ionized 130In, 130Cs -molecular ions [40Ca90Br]+ T1/2 = (195 ± 35) ms Exp. T1/2 excludes explosive He-burning favored at that time; supports supernova scenario. Model predictions at that time: 30 ms ≤ T1/2 ≤ 1.2 s

  13. The FK2L waiting-point approach (I) 30

  14. The FK2L waiting-point approach (II)

  15. The FK2L waiting-point approach (III)

  16. The FK2L waiting-point approach (IV) birth of N=82 “shell-quenching” idea …

  17. Request: Selectivity ! the Ag “needle” in the Cs “haystack” 50 800 >105 Sb Te I Xe Sn Cd In Ag Cs • Remember • T1/2 of 130Cd at SC-ISOLDE • non-selective plasma ion-source • selective quartz transfer line • selective ßdn-counting … hunting for N=82 129Ag Obviously not sufficient High background from - surface-ionized 130In, 130Cs - molecular ions [40Ca90Br]+ Request: additional selectivity steps • Fast UCx target • Neutron converter • Laser ion-source • Hyperfine splitting • Isobar separation • Repeller • Chemical separation • Multi-coincidence setup developed since 1993

  18. RILIS experiments at ISOLDE Since ca. 1995 many experiments with RILIS by Mainz group • gross properties / new isotopes • e.g. Y. Jading et al., n-rich Ag(1996) • M. Hannawald et al., n-rich Mn (1999) • M. Hannawald et al., n-rich Cd (2000) • I. Dillmann et al., n-rich In (2002) • O. Arndt et al., n-rich Ag to Sb (2005) • detailed γ-spectroscopy • e.g. G. Lhersonneau et al., n-rich Rb to Tc • (ca. 20 papers since 1995) • T. Kautzsch et al., 124, 126, 128Cd levels (2000) • J. Shergur et al., 134 – 136Sndecays (2002) • I. Dillmann et al., 130Cd decay (2003) • C. Jost et al., 127, 129, 131Cd decays (2009)

  19. 131In82 131In82 49 49 Our last experiment at ISOLDE Surface chemistry Proton-hole states in UCx-target; neutron converter; 180 ms data collection per p-pulse; quartz transfer line at 820°C main b-feeding to 4-6 MeV Eℓ (keV) 68 ms 131 Cd decay 2439 pf5/2 2741 Laser ON Laser OFF Cs 2439 keV 131 Cd 988 pp3/2 1290 pp1/2 302 (b – isomer) pg9/2 0 Cs 988 keV 131 Cd Energy- splitting Hyde (1980) Leander (1984) Brown (1998) Exp. 1.4 MeV 1.1 MeV pp1/2 – pp3/2 0.988 MeV 0.6 MeV pp1/2 – pf5/2 1.3 MeV 2.6 MeV 2.6 MeV 2.439 MeV

  20. Z N Snapshots: r-Process paths for different neutron densities Today, altogether 60 r-process nuclei known 82 84 86 88 90 92 94 Ba Cs Xe heaviest isotopes with measured T1/2 I Te Sb Sn In Cd Ag g9/2 Pd Rh Ru Tc Mo Nb Zr p1/2 Y Sr Rb p3/2 Kr Br Se As f5/2 Ge Ga Zn Cu Ni f7/2 Co Fe 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 8082 h11/2 d3/2 g9/2 d5/2 g7/2 s1/2

  21. nn=1020 Z N r-Process path for nn=1020 82 84 86 88 90 92 94 Ba Cs Xe I Te Sb Sn In Cd Ag Pd Rh Ru Tc Mo Nb Zr Y Sr Rb Kr Br Se As Ge Ga Zn Cu Ni Co Fe 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 8082 „waiting-point“ isotopes at nn=1020 freeze-out

  22. nn=1020 nn=1023 Z N r-Process paths for nn=1020 and 1023 82 84 86 88 90 92 94 Ba Cs Xe I Te Sb Sn In Cd Ag Pd Rh Ru Tc Mo Nb Zr Y Sr Rb Kr Br Se As Ge Ga Zn Cu Ni Co Fe 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 8082 „waiting-point“ isotopes at nn=1023 freeze-out (T1/2 exp. : 28Ni – 31Ga, 36Kr, 37Rb,47Ag – 51Sb)

  23. nn=1020 nn=1023 nn=1026 Z N r-Process paths for nn=1020, 1023 and 1026 82 84 86 88 90 92 94 Ba Cs Xe I Te Sb Sn In Cd Ag Pd Rh Ru Tc Mo Nb Zr Y Sr Rb Kr Br Se As Ge Ga Zn Cu Ni Co Fe 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 8082 „waiting-point“ isotopes at nn=1026 freeze-out (T1/2 exp. : 28Ni, 29Cu, 47Ag – 50Sn)

  24. Summary “waiting-point” model seed Fe superposition of nn-components …largely site-independent! “weak” r-process (later secondary process; explosive shell burning?) “main” r-process (early primary process; SN-II?) Th/Eu Th/Hf Th/U 13.6 ± 2.8 Gyr Kratz et al., Ap.J. 662 (2007) Frebel & Kratz, IAU 258 (2009) Roederer, Kratz et al., Ap.J. (2009)

  25. From waiting-point to high-entropy wind model Now, more realistic r-process model High-Entropy Wind of SN II full dynamical network (Basel model); “best” nuclear-physics input (Mainz & LANL) start with T9 10 3 ≤ T9≤ 6a-process α-rich freeze-out at T9 ≈ 3  n-rich seed beyond N=50 (94Kr, 100Sr, 95Rb …) for subsequentr-process avoids N=50 “bottle neck” in classical model ! Threecorrelatedparameters: electron abundanceYe= Yp = 1 – Yn radiation entropy S ~ T³/r expansion speed vexp durations taand tr „strength“ formula (Farouqi, PhD Mainz 2005)

  26. Elemental abundance a-process neutron-capture process Atomic number. Z Parameters HEW model  Y(Z) Ye=0.45 α n No neutrons no r-process! seed HEW model relative to Nr, “residuals” underproduction Fe – Rb additional processes? Pignatari et al.  new s Fröhlich et al. νp overproduction Sr - Ag

  27. HEW nucleosynthesis components as function of S Type of process a-process bdn-proc. “weak” r-proc. “main” r-process Yn/Yseed 15-150 1-10 <1 0 Farouqi, Kratz (2007)

  28. Halo stars vs. HEW model: Sr/Y/Zr as fct. of [Fe/H], [Eu/H] and [Sr/H] HEW model (S≥10) average Halo stars Robust Sr/Y/Zr abundance ratios, independent of metallicity, r-enrichment, α-enrichment. Same nucleosynthesis component: α-process, NOT r-process

  29. Recent observations vs. HEW-model predictions: Pd Pd relation to α-element Sr average Halo stars -1.5 < [Eu/H] < -0.6 log(Pd/Sr)  - 0.95(0.09) HEW model log(Pd/Sr) =- 0.81 (“r-rich”) - 1.16(“r-poor”) Pd relation to r-element Eu average Halo stars -1.5 < [Eu/H] < -0.6 log(Pd/Eu)  +0.81(0.07) HEW model log(Pd/Eu) = +1.25 (Pd α+r) +0.89(“r-rich”) +1.45 (”r-poor”) r-poor stars ([Eu/H]<-3) indicate TWO nucleosynthesis components for 46Pd: Pd/Sr  uncorrelated, Pd/Eu  correlated with “main” r-process

  30. Process duration [ms] Entropy S FRDMETFSI-Q Remarks • 54 57 A≈115 region • 209 116 top of A≈130 peak • 422 233 REE pygmy peak • 691339 top of A≈195 peak • 1290 483 Th, U • 2280 710 fission recycling • 300 4310 1395 “ “ significant effect of “shell-quenching” below doubly-magic 132Sn Reproduction of Nr, Superposition of 27 S-components; weightingaccording to Yseed FRDM ETFSI-Q No exponential fit to Nr, !

  31. Summary • Yesterday: - 20 years of hard work to develop „clean“ ISOL-beams; - identification of ca. 60 r-process isotopes (68Fe – 139Sb); - the site-independent “waiting-point model“ has been a useful working-horse in the past. • Today: • - within the “HEW SN II scenario“, the full production of the Nr, distribution • is possible within 500 ms and Smax.300 kB/baryon; • - the SS “r-residuals“ are a superposition of 4 distinct nucleosynthesis • components: pure α, n-richα+βdn, weak-r, main-r; • - the two low-S components (α and α+bdn) are not tightly correlated with • the main r-process; • - most of present UMP halo-star elemental abundances are reproduced, • from r-rich “Sneden star“ to r-poor “Honda star“. • Tomorrow: - comparison of HEW predictions withisotopicabundances in stars and interstellar grains; • - coupling of HEW network to hydrodynamical SN II calculations.

  32. Claus, it’s your fault …

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