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Studies of r-process nuclei with fast radioactive beams

Studies of r-process nuclei with fast radioactive beams. Fernando Montes National Science Superconducting Cyclotron Joint Institute for Nuclear Astrophysics. Supernova 2002bo in NGC 3190. Outline. Motivation: Origin of the elements heavier than iron

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Studies of r-process nuclei with fast radioactive beams

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  1. Studies of r-process nuclei with fast radioactive beams Fernando Montes National Science Superconducting Cyclotron Joint Institute for Nuclear Astrophysics Supernova 2002bo in NGC 3190

  2. Outline • Motivation: Origin of the elements heavier than iron • Signatures of different nucleosynthesis processes in the solar system and in the abundances of metal-poor stars Supernova 1997bs in M66 • Nuclear properties required for an understanding of the r-process • R-process experiments at the NSCL • Conclusions

  3. Dense clouds Big Bang Creation of the elements Nucleosynthesis is a gradual, still ongoing process: M~104..6 Mo 108 y Condensation Star formation M > 0.7Mo Interstellar medium Life of a star continuousenrichment,increasingmetallicity Nucleosynthesis: Stable burning H, He 106..10 y Dust mixing Nucleosynthesis: Explosive burning Remnants(White dwarf, neutron star, black hole) Death of a star(Supernova, planetary nebula) Nucleosynthesis

  4. Mass known Half-life known nothing known np process Light element primary process LEPP Creation of the elements: nucleosynthesis protons neutrons Most of the heavy elements (Z>30) are formed in neutron capture processes, either the slow (s) or rapid (r) process p process r process rp process stellar burning s process Big Bang Cosmic Rays

  5. Contribution of different processes Ba: s-process Eu: r-process Contribution of the diff. processes to the solar abundances s-process: Astrophysical model Ba p-process: Astrophysical model Eu r-process: Abundance of enriched-r-process star LEPP = solar-s-p-r

  6. underabundant agreement stars and solar “Solar r” e Metal-poor star abundances Metallicity (amount of iron) ~ time Very metal-poor stars are enriched by just a few nucleosynthesis events R-process + LEPP

  7. b-decay G(Z,A+1) ~ nnT-3/2 R-process basics G(Z,A) Y(Z,A+1) Sn(Z,A+1)/kT e Y(Z,A) Element formation beyond iron involving rapid neutron capture and radioactive decay High neutron density Seed Waiting point (n,g)-(g-n) equilibrium Waiting point approximation

  8. Nuclear physics in the r-process • Fission rates and distributions: • n-induced • spontaneous • b-delayed b-delayed n-emissionbranchings(final abundances) b-decay half-lives(progenitor abundances, process speed) n-capture rates Smoothing progenitor abundances during freezeout n-physics ? • Masses: • Sn location of the path • Qb, Sn theoretical b-decay properties, • n-capture rates Seed productionrates

  9. r-process beams at the NSCL Coupled Cyclotron Facility r-processbeam Future: low energy beams1-2 MeV/u Delta E Tracking (=Momentum) TOF Primary beam100-140 MeV/u Experimental station Be target Fast beams fromfragmentation with Coupled Cyclotrons

  10. Fit (mother, daughter, granddaughter, background)  T1/2 105Zr Implantation station: The Beta Counting System (BCS) • Implantation DSSD:x-y position (pixel), time • Decay DSSD:x-y position (pixel), time Veto light particles from A1900 6 x SSSD (16) 4 x Si PIN DSSD (40×40) Ge Silicon PIN Stack Beta calorimetry

  11. 3He Proportional Counters BF3 Proportional Counters Polyethylene Moderator Boron Carbide Shielding G. Lorusso, J.Pereira et al., PoS NIC-IX (2007) Implantation station: The Neutron Emission Ratio Observer (NERO)

  12. Nuclei with b-decay Nuclei with b-decay AND neutron(s) Pn-values Implantation station: The Neutron Emission Ratio Observer (NERO) Measurement of neutron in “delayed” coincidence with b-decay

  13. 16 SeGA detectors around the BCS Efficiency ~7.5% at 1 MeV W.Mueller et al., NIMA 466, 492 (2001) Implantation station: The Segmented Germanium Array (SeGA)

  14. b-delayed gamma spectroscopy of daughter Implantation station: The Segmented Germanium Array (SeGA)

  15. NSCL reach 120Rh 107Zr 78Ni Astrophysics motivated experiments Known before Critical region NSCL Experiments done • P. Hosmer, P. Santi, H. Schatz et al. • F. Montes, H. Schatz et al. • B. Tomlin, P.Mantica, B.Walters et al. • J. Pereira, K.-L.Kratz, A. Woehr et al. • M. Matos, A. Estrade et al. 69Fe

  16. +100 Exp. 78Ni T1/2 = 110 ms -60 I) b-decay half-live of 78Ni50 waiting point Predicted 78Ni T1/2: 460 ms P. Hosmer et al. PRL 94, 112501 (2005) • Half-live of ONE single waiting-point nucleus: • Speeding up the r-process clock • Increase matter flow through 78Ni bottle-neck • Excess of heavy nuclei (cosmochronometry)

  17. II) “Gross” nuclear structure around 120Rh45 from b-decay properties Inferring (tentative) nuclear deformations with QRPA model calculations F. Montes et al., PRC73, 35801 (2006) • 120Rh Pn value direct input in r-process calculations • Half-lives and Pn-values sensitive to nuclear structure • Over-predictions for Ru and Pd isotopes: larger Q-values or problems in the GT strength • Need microscopic calculations beyond QRPA

  18. II)Probing the strength of N=82 shell-closure from b-delayed g-spectroscopy B.Walters, B.Tomlin et al., PRC70 034414 (2004) • No evidence of shell-quenching when approaching shell closure in Pd isotopes up to N=74 • Need more E(2+) data at 74<N<82 • R-process abundances at A~115 are directly affected by the strength of shell closure • Experimental evidence is mixed: 130Cd E(2+) does not show evidence of quenching

  19. III) b-decay properties of Zr isotopes beyond mid-shell N=66 J.Pereira et al., in preparation • Possible double-magic Z=40, N=70: Effects from spherical shape of 110Zr70 observable at 66<N<70? • Shorter half-life of (potential) waiting-point 107Zr affect predicted r-process abundances at A~110 • Mean-field model calculations predict N=82 shell-quenching accompanied by a new harmonic oscillator shell at N=70

  20. Nuclear Physics Same “astrophysical model”, different nuclear physics … • Theoretical models are in the majority of cases within a factor of 3 from observed abundance • Models agree within a factor of 3-4 except for In (Z=49) and Lu (Z=71) Montes et al. AIP Conf. Proc., 947, 364 (2007). This “agreement” however is not good enough to calculate LEPP isotopic abundances

  21. If it involves high neutron densities peak should be here If it involves low neutron densities peak should be here instead Light element primary process (LEPP) LEPP = solar-s-p-r

  22. 107Zr Future Facility Reach(here ISF) 78Ni Reach for future r-process experiments with new facilities (ISF, FAIR, RIBF…) Almost all b-decay half-lives of r-process nuclei at N=82 and N=126 will be reachable with ISF Known before NSCL reach NSCL Experiments done

  23. Conclusions • Despite many years of intensive effort, the r-process site and the astrophysical conditions continues to be an open question. New LEPP process complicates the situation • Besides being direct r-process inputs, beta-decay properties of exotic nuclei turned out to be an effective probe for nuclear structure studies of exotic nuclei • R-process experimental campaigns at NSCL provide beta-decay properties of r-process nuclei and comparisons with theoretical calculations will improve astrophysical r-process calculations • New facilities will largely extend the r-process regions accessible (FAIR, ISF). Meanwhile, new observations (SEGUE) and new measurements of exotic n-rich nuclei are highly necessary

  24. More metal-poor stars Qian & Wasserburg Phys. Rep 442, 237 (2007); Montes et al. ApJ 671 (2007) Slope indicatesratio of light/heavy Z=39 Solar r [Y/Eu] [La/Eu] Z=57 Some stars have light elementsat solar level Z=47 [Ag/Eu] [Sm/Eu] Light elementsat high enrich- ment fairly robust and subsolar Heavy r-patternrobust andagrees with solar Z=62 [Eu/Fe] [Eu/Fe] Metal poor star = r-process + Light element primary process Multiple nucleosynthesis processes in the early universe

  25. Summary features of fast beams from fragmentation Fast beams from fragmentation complement other techniques and they have these particular features : • High selectivity even with mixed (“cocktail”) beams because due to its high • energy, relevant particle properties can be detected (TOF, energy losses …) • Fast beam – negligible decay losses (~100 nanoseconds..) • Production of broad range of rare isotope beams with a single primary beam Typical beam energies: 50-1000 MeV/nucleon Typical new rare isotope beams can be produced within ~ 1h

  26. Nuclear physics behind everything… Mass number a-nuclei12C,16O,20Ne,24Mg, …. 40Ca,44Ti GapB,Be,Li r-process peaks (nuclear shell closures) s-process peaks (nuclear shell closures) U,Th Fe peak(width !) Au Pb

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