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. 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 Nuclear properties required for an understanding of the r-process R-process experiments at the NSCL Conclusions Supernova 1997bs in M66 Outline

3. Nucleosynthesis is a gradual, still ongoing process: Life of a star Death of a star (Supernova, planetary nebula) Interstellar medium Remnants (White dwarf, neutron star, black hole) Nucleosynthesis: Stable burning Nucleosynthesis: Stable burning Nucleosynthesis: Explosive burning Nucleosynthesis: Explosive burning H, He continuous enrichment, increasing metallicity Condensation M~10 4..6 M o 10 8 y 10 6..10 y M > 0.7M o Star formation Dust mixing Nucleosynthesis Dense clouds Big Bang Creation of the elements

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

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

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

7. F. Montes Nuclear Astrophysics Element formation beyond iron involving rapid neutron capture and radioactive decay Waiting point (n,  )-(  -n) equilibrium  -decay Seed  igh neutron density G(Z,A) ~ n n T -3/2 G(Z,A+1) e S n (Z,A+1)/kT Y(Z,A) Y(Z,A+1) Waiting point approximation R-process basics

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

9. F. Montes Nuclear Astrophysics Future: low energy beams1-2 MeV/u Fast beams from fragmentation with Coupled Cyclotrons r-process beams at the NSCL Coupled Cyclotron Facility Primary beam 100-140 MeV/u Be target Tracking (=Momentum) TOF Delta E r-process beam Experimental station

10. F. Montes Nuclear Astrophysics Silicon PIN Stack 4 x Si PIN DSSD (  Implantation DSSD: x-y position (pixel), time Decay DSSD: x-y position (pixel), time 6 x SSSD (16) Ge Implantation station: The Beta Counting System (BCS) Veto light particles from A1900 Beta calorimetry 105 Zr Fit (mother, daughter, granddaughter, background)  T 1/2

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

12. F. Montes Nuclear Astrophysics Implantation station: The Neutron Emission Ratio Observer (NERO) Nuclei with  -decayNuclei with  -decay AND neutron(s) P n -values Measurement of neutron in “delayed” coincidence with  -decay

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

14. F. Montes Nuclear Astrophysics Implantation station: The Segmented Germanium Array (SeGA)  -delayed gamma spectroscopy of daughter

15. F. Montes Nuclear Astrophysics Known before 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. Critical region 78 Ni 107 Zr NSCL reach 120 Rh Astrophysics motivated experiments 69 Fe

16. Predicted 78 Ni T 1/2 : 460 ms P. Hosmer et al. PRL 94, 112501 (2005) Exp. 78 Ni T 1/2 = 110 ms +100 -60 I )  -decay half-live of 78 Ni 50 waiting point Half-live of ONE single waiting-point nucleus:  Speeding up the r-process clock  Increase matter flow through 78 Ni bottle-neck  Excess of heavy nuclei (cosmochronometry)

17. F. Montes Nuclear Astrophysics II ) “Gross” nuclear structure around 120 Rh 45 from  -decay properties F. Montes et al., PRC73, 35801 (2006) Inferring (tentative) nuclear deformations with QRPA model calculations 120 Rh Pn value direct input in r-process calculations Half-lives and P n -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. F. Montes Nuclear Astrophysics II )  Probing the strength of N=82 shell- closure from  -delayed  -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: 130 Cd E(2+) does not show evidence of quenching

19. J.Pereira et al., in preparation Possible double-magic Z=40, N=70: Effects from spherical shape of 110 Zr 70 observable at 66<N<70? Shorter half-life of (potential) waiting-point 107 Zr 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 III )  -decay properties of Zr isotopes beyond mid-shell N=66

20. F. Montes Nuclear Astrophysics 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) Same “astrophysical model”, different nuclear physics … This “agreement” however is not good enough to calculate LEPP isotopic abundances Montes et al. AIP Conf. Proc., 947, 364 (2007).

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

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

23. F. Montes Nuclear Astrophysics 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 Conclusions

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

25. F. Montes Nuclear Astrophysics 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 Summary features of fast beams from fragmentation Fast beams from fragmentation complement other techniques and they have these particular features :

26. F. Montes Nuclear Astrophysics Gap B,Be,Li  -nuclei 12 C, 16 O, 20 Ne, 24 Mg, …. 40 Ca, 44 Ti Fe peak (width !) s-process peaks (nuclear shell closures) r-process peaks (nuclear shell closures) Au Pb U,Th Nuclear physics behind everything… Mass number