Studies of r-process nuclei with fast radioactive beams

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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 beamsFernando MontesNational Science Superconducting CyclotronJoint Institute for Nuclear AstrophysicsSupernova 2002bo in NGC 3190Outline
  • 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
  • Dense cloudsBig BangCreation of the elementsNucleosynthesis is a gradual, still ongoing process:M~104..6 Mo108 yCondensationStar formationM > 0.7MoInterstellarmediumLife of a starcontinuousenrichment,increasingmetallicityNucleosynthesis:Stable burningH, He106..10 yDust mixingNucleosynthesis:Explosive burning Remnants(White dwarf, neutron star, black hole)Death of a star(Supernova, planetary nebula)NucleosynthesisMass knownHalf-life knownnothing knownnp processLight element primary processLEPPCreation of the elements: nucleosynthesisprotonsneutronsMost of the heavy elements (Z>30) are formed in neutron capture processes, either the slow (s) or rapid (r) processp processr processrp processstellar burnings processBig BangCosmic RaysContribution of different processesBa: s-processEu: r-processContribution of the diff. processes to the solar abundancess-process: Astrophysical modelBap-process: Astrophysical modelEur-process:Abundance of enriched-r-process starLEPP = solar-s-p-runderabundantagreement stars and solar“Solar r”eMetal-poor star abundancesMetallicity (amount of iron) ~ timeVery metal-poor stars are enriched by just a few nucleosynthesis eventsR-process + LEPPb-decayG(Z,A+1)~ nnT-3/2R-process basicsG(Z,A)Y(Z,A+1)Sn(Z,A+1)/kTeY(Z,A)Element formation beyond iron involving rapid neutron capture and radioactive decayHigh neutron densitySeed Waiting point(n,g)-(g-n) equilibriumWaiting point approximationNuclear 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 ratesSmoothing progenitor abundances during freezeoutn-physics ?
  • Masses:
  • Sn location of the path
  • Qb, Sn theoretical b-decay properties,
  • n-capture rates
  • Seed productionratesr-process beams at the NSCL Coupled Cyclotron Facilityr-processbeamFuture: low energy beams1-2 MeV/uDelta ETracking(=Momentum)TOFPrimary beam100-140 MeV/uExperimental stationBe targetFast beams fromfragmentation with Coupled CyclotronsFit (mother, daughter, granddaughter, background)  T1/2105ZrImplantation station: The Beta Counting System (BCS)
  • Implantation DSSD:x-y position (pixel), time
  • Decay DSSD:x-y position (pixel), time
  • Veto light particles from A19006 x SSSD (16) 4 x Si PINDSSD (40×40)Ge Silicon PIN StackBeta calorimetry3He ProportionalCountersBF3 Proportional CountersPolyethylene ModeratorBoron Carbide ShieldingG. Lorusso, J.Pereira et al., PoS NIC-IX (2007)Implantation station: The Neutron Emission Ratio Observer (NERO)Nuclei with b-decayNuclei with b-decay AND neutron(s)Pn-valuesImplantation station: The Neutron Emission Ratio Observer (NERO)Measurement of neutron in “delayed” coincidence with b-decay16 SeGA detectors around the BCS Efficiency ~7.5% at 1 MeVW.Mueller et al., NIMA 466, 492 (2001)Implantation station: The Segmented Germanium Array (SeGA)b-delayed gamma spectroscopy of daughter Implantation station: The Segmented Germanium Array (SeGA)NSCL reach120Rh107Zr78NiAstrophysics motivated experimentsKnown beforeCritical regionNSCL 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+100Exp. 78Ni T1/2 = 110 ms -60I) b-decay half-live of 78Ni50 waiting pointPredicted 78Ni T1/2: 460 msP. 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)
  • II) “Gross” nuclear structure around 120Rh45 from b-decay propertiesInferring (tentative) nuclear deformations with QRPA model calculationsF. 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
  • II)Probing the strength of N=82 shell-closure from b-delayed g-spectroscopyB.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
  • III) b-decay properties of Zr isotopes beyond mid-shell N=66J.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
  • Nuclear PhysicsSame “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 abundancesIf it involves high neutron densities peak should be hereIf it involves low neutron densities peak should be here insteadLight element primary process (LEPP)LEPP = solar-s-p-r107ZrFuture Facility Reach(here ISF)78NiReach 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 ISFKnown beforeNSCL reachNSCL Experiments doneConclusions
  • 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
  • More metal-poor starsQian & Wasserburg Phys. Rep 442, 237 (2007); Montes et al. ApJ 671 (2007)Slope indicatesratio of light/heavyZ=39Solar r[Y/Eu][La/Eu]Z=57Some stars havelight elementsat solar levelZ=47[Ag/Eu][Sm/Eu]Light elementsat high enrich-ment fairly robust and subsolarHeavy r-patternrobust andagrees with solarZ=62[Eu/Fe][Eu/Fe]Metal poor star =r-process +Light element primary processMultiple nucleosynthesis processes in the early universeSummary features of fast beams from fragmentationFast 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/nucleonTypical new rare isotope beams can be produced within ~ 1hNuclear physics behind everything…Mass numbera-nuclei12C,16O,20Ne,24Mg, …. 40Ca,44TiGapB,Be,Lir-process peaks (nuclear shell closures)s-process peaks (nuclear shell closures)U,ThFe peak(width !)AuPb
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