Jorge Pereira (pereira@nscl.msu) National Superconducting Cyclotron Laboratory (NSCL/MSU)

1. Jorge Pereira, INPC 2007 Studies of r-process nuclei at NSCL Astrophysical importance of b-decay studies in the understanding of the r-process Jorge Pereira (pereira@nscl.msu.edu) National Superconducting Cyclotron Laboratory (NSCL/MSU) Joint Institute for Nuclear Astrophysics (JINA)

2. M57 Ring Nebula. • Synthesis of Heavy Elements • An overview on astronomical abundance observations SNR 0103-72.6 Credit: NASA/CXC/PSU/S.Park et al.

3. Observed Solar-System Heavy-Element abundances Solar Different processes contribute to the observed Heavy-Element abundances r ≈ “leftovers” ( Solar – s ) s-process p-process r-process log e = log10 (Yel/YH)+12

4. J.Cowan and C.Sneden, Nature 440, 1151 (2006) Missing abundance  Another process contributing to solarlight r-residuals? CS22892-052 HD 115444 BD+1703248 CS 31082-001 HD221170 R-process elemental abundances: Solar-System vs. Metal-Poor Stars (MPS) Consistent abundances (MPS and Solar) pattern for Z > 47 Very ROBUST r-process (MAIN r-process)

5. LEPP elemental= HD122563– Main LEPP elemental= solar– s-process– Main What about less enriched stars? LEPP process C. Travaglio et al., ApJ 601, 864 (2004) LEPP contributes to r-process elemental abundances Very consistent pattern  Second ROBUST process F. Montes et al., submitted to ApJ

6. How do these processes operate? • What is their site? Comparing results (e.g. classical approach) with observed abundance pattern D. Swesty, A. Calder, E.Wang, D.Bock, NCSA (1998) E0102-72.2

7. Classic model. Different Nuclear Physics ETFSI-Q ETFSI-1 C.Freiburghaus et al., ApJ516, 381 (1999) Mass number What are these models sensitive to? Astrophysics VS. Nuclear Physics Astrophysical conditions: parameterized studies (e.g nn, T, tirr)…freeze-out, neutrinos Nuclear Physics (mostly theoretical): b-decay properties (T½ , Pn, masses) Astrophysical r-process model calculations are very sensitive to Nuclear Physics of nuclei involved

8. Why b-decay studies in the search for the r-process and LEPP sites? • NSCL experiments with Exotic Beams

9. b-decay properties in the r-process • Half-lives of r-process nuclei: • The clock of the r-process • What are the bottle-necks of matter flow?  Abundance pattern prior freeze-out b-decay studies of very exotic neutron-rich nuclei at NSCL • T1/2 and Pn (gross b-decay properties): • First insights into shell structure at low energies and above Sn(Deformation, nucleon-nucleon interaction, new magic numbers, etc…) • Pn-values around r-process nuclei:What is the path followed by matter flow after freeze-out(Abundance pattern post freeze-out)

10. Ion Source K500 K1200 Coupled in 2000 Exotic beam delivery: The CCF : Operated 1982-1989 : Operated 1989-1999

11. Ion Source K500 K1200 A1900 Exotic beam delivery: The A1900 in-flight separator

12. N3 vault Ion Source K500 DE PIN DE PIN (a.u.) ToF Im2-N3 107Zr A1900 K1200 ToF Im2-N3 (a.u.) Exotic beam delivery: The A1900 in-flight separator Im2 • Separation and identification of exotic beam: ToF vs. DE

13. N3 vault Ion Source K500 Im2 A1900 K1200 Exotic beam delivery: The A1900 in-flight separator • Separation and identification of exotic beam: ToF vs. DE • Exotic beam  Implantation station (in the N3 vault)

14. Fit (mother, daughter, granddaughter, background)  T1/2 105Zr J.J. Prisciandaro et al., NIMA 466, 492 (2001) Implantation station: The Beta Counting System (BCS) • Implantation DSSD:x-y position (pixel), time • Veto light particles from A1900 • Decay DSSD:x-y position (pixel), time Silicon PIN Stack 4 x Si PIN 6 x SSSD (16) DSSD (40×40) Ge

15. Implantation station: The Beta Counting System (BCS) • Implantation DSSD:x-y position (pixel), time • Veto light particles from A1900 • Decay DSSD:x-y position (pixel), time Silicon PIN Stack 4 x Si PIN 6 x SSSD (16) • Beta calorimetry DSSD (40×40) Ge

16. 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)

17. 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

18. 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)

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

20. Results from b-decay r-process campaigns at NSCL

21. NSCL reach 129Rh 107Zr 78Ni Critical region NSCL r-process campaigns – MSU/Mainz/Notre Dame/Maryland 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.

22. Predicted 78Ni T1/2: 460 ms Exp. 78Ni T1/2 = 110 ms I) b-decay half-live of 78Ni50 waiting point +100 -60 • 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) P. Hosmer et al. PRL 94, 112501 (2005)

23. F. Montes et al., PRC73, 35801 (2006) II) “Gross” nuclear structure around 120Rh65 from b-decay properties Inferring (tentative) nuclear deformations with QRPA model calculations • Half-lives and Pn-values sensitive to nuclear structure at different energies: (Complementary information to infer nuclear deformation) • Need microscopic calculations beyond QRPA • Possible signatures of new shell-structure when approaching r-process path

24. II)Probing sustainability of N=82 at 120Pd from b-delayed g-spectroscopy B.Walters, B.Tomlin et al., PRC70 034414 (2004) • No evidence of shell-quenching when approaching waiting point128Pd at N=74 • Need more E(2+) data at 74<N<82

25. Shorter half-life of (potential) waiting-point 107Zr67 may affect predicted r-process abundances at A~110 • QRPA consistent with spherical shapes beyond mid-shell (possible signatures of double magic N=40 N=70?) • Urgent need of microscopic calculations beyond QRPA J.Pereira et al., in preparation III) b-decay properties of Zr isotopes beyond mid-shell N=66 • A ≈110: Calculations fail to reproduce r-process abundance pattern below A=130 peak • N~66 is at mid-shell: Shape transitions between sudden onset of deformation at N=60 and closed shell at N=82 • Possible double-magic Z=40, N=70: Effects from spherical shape of 110Zr70 observable at 66<N<70? J. Dowaczewski et al.,PRL72, 981 (1994)

26. Fine!…but what do we do meanwhile? • Keep observing abundances and wait for these facilities… • Continue r-process studies with theoretically calculated b-decay properties (to be confirmed with new measurements) 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 pps

27. Conclusions • Despite many years of intensive effort, the r-process site continues to be one of the BIG SCIENCE QUESTIONS for the new century – NAS REPORT. 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 an extensive data body of beta-decay properties of r-process nuclei. Comparisons with calculations microscopic models will improve astrophysical r-process calculations • New facilities will largely extend the r-process regions accessible. Meanwhile, new observations (SEGUE) and new measurements of exotic n-rich nuclei are highly necessary

28. Thanks to: • NSCL/MSU:Hendrik Schatz, Paul Mantica Ana Becerril, Tom Elliot, Alfredo Estrade, Ron Fox, Daniel Galaviz, Tom Ginter, Mark Hausmann, Paul Hosmer, Linda Kern, Giuseppe Lorusso, Milan Matoš, Fernando Montes • Univ. Notre Dame: Andreas Woehr Ani Aprahamian, Matt Quinn • Mainz Universität: Karl-Ludwig Kratz Oliver Arnd, Ruben Kessler, Stefan Hennrich, Bernd Pfeiffer, Florian Schertz • University of Maryland: William Walters • JINA and VISTAR collaborations

29. Backup Slides

30. The Big Question What is the origin of heavy elements from iron to uranium ? One of the “Eleven Science Questions for the New Century” (NAS report “Connecting Quarks with the Cosmos”) Do we understand the observed heavy-element abundances ?

31. What about less enriched stars? (Leftover of Leftover) Some stars (e.g. HD122563) show enrichment of lighter elements (Sr-Ag) compared to MAIN r-process –F.Montes et al., submitted to ApJ – Similar observations for Sr, Zr by C.Travaglio et al. Light Element Primary Process (LEPP) – C. Travaglio et al., ApJ 601, 864 (2004) –

32. Slope indicatesratio of light/heavy) changes for lessenriched stars Some stars have light r-elementsat solar level Light r-elementsat high enrichmentfairly robust andsubsolar Heay r-patternrobust andagrees with solar What about less MAIN r-process enriched stars? [Eu/Fe] Enrichment with main r-process Light r / Heavy r (Eu) Heavy r / Heavy r (Eu) Solar r [La/Eu] [Y/Eu] Montes et al. to be published [Sm/Eu] [Ag/Eu] [Eu/Fe] [Eu/Fe] • Consistent with second process producing also Sr-Ag LEPP, identified by Travaglio et al. 2004

33. Trying to fit LEPP pattern with n-capture flow • Low nn and high nn fit low Z • Low nn also fits small high Z abundances

34. Conclusions depend on s-process s-process from Simmerer et al. (Cowan et al.) s-process from Travaglio et al. • Need reliable s-process (models and nuclear data) • Clearly something is going on for Z < ~50 (“light” p-process elements) Need to look at many stars …

35. 10 Hot bubble Classic model. Different Nuclear Physics Classic model ETFSI-Q 10 ETFSI-1 10 Abundances (Si≡106) 10 10 10 C.Freiburghaus et al., ApJ516, 381 (1999) Mass number Mass number What are these models sensitive to? Astrophysics VS. Nuclear Physics Astrophysical conditions: parameterized studies (e.g nn, T, tirr) Nuclear Physics (mostly theoretical): b-decay properties (T½ , Pn), masses Same Nuclear Physics Astrophysical r-process model calculations are very sensitive to Nuclear Physics of nuclei involved • Freeze-out • Neutrino presence • n-capture rates • Fission barriers

36. Waiting point approximation Definition: ASSUME (n,g)-(g,n) equilibrium within isotopic chain How good is the approximation ? This is a valid assumption during most of the r-processBUT: freezeout is neglected Freiburghaus et al. ApJ 516 (2999) 381 showed agreement with dynamical models Consequences During (n,g)-(g,n) equilibrium abundances within an isotopic chain are given by: • Time independent • Can treat whole chain as a single nucleus in network • Only slow beta decays need to be calculated dynamically • Neutron capture rate independent(During most of the r-process n-capture rates do not matter !)

37. Conditions which fit the A≈80 and A ≈ 130 r-process abundance peaks K.-L. Kratz et al., ApJ 403, 216 (1993) Inferring r-process conditions from “site-independent” models • Parameterized Astrophysical conditions (e.g. nn, T, tirr)

38. Classic model with different Nuclear Physics ETFSI-Q BUT very sensitive to Nuclear Physics!!! Conditions which fit the A≈80 and A ≈ 130 r-process abundance peaks different components with large nn, T ETFSI-1 Mass number C.Freiburghaus et al., ApJ 516, 381 (1999) K.-L. Kratz et al., ApJ 403, 216 (1993) Conditions for the r-process from “site-independent” models • Parameterized Astrophysical conditions (e.g. nn, T, tirr) • Nuclear Physics of nuclei involved (mostly theoretical)

39. 2 possible scenarios: 1) high S, moderate Ye2) low S, low Ye Neutron to seed ratios • n/seed is higher for • lower Ye(more neutrons) • higher entropy(low density  low 3a-rate  • slow seed assembly) • faster expansion(less time to assemble seeds) (Meyer & Brown ApJS112(1997)199)

40. Production of Primary Beam:Coupled Cyclotron Facility, CCF Production of RNB:A1900 in-flight separator(Fragmentation reactions…and Fission (in progress)) • NERO: b-delayed n-emission probabilities (Pn) Beta Counting System: Half-lives (T1/2) • SeGA: b-delayed and “direct” g-spectroscopy b-decay r-process motivated experiments at NSCL Experiments with implanted RNB

41. I) b-decay half-live of 78Ni waiting-point: testing model calculations Results from earlier experiment in Ni Half-lives and Pn-values sensitive to nuclear structure at different energies: complementary information to rule out models

42. Decay-curves fits (mother, daughter, granddaughter) 106Zr 107Zr 105Zr 104Zr 107Zr MLH: Find maximum of Likelihood function (sum of join probability density for 1, 2 and 3-member decay chains) Results: b-decay Half-lives (even with low statistics)

43. Calculated b-decay properties of r-process nuclei with FRDM-QRPA Macro/Microscopic model global applicability (better suited for r-process models) 1. Calculation of ground-state masses and deformation parameters FRDM + Strutinsky microscopic corrections (Shell + Pairing) 2. Use deformation parameters to determine single-particle levels f (folded-Yukawa + Lipkin-Nogami) 3. Calculate Gamow-Teller b-strength function using calculated f and adding residual interaction VGT=2cGT:b1-• b1+: with operatorb1± =∑i (st±)i Sensitivity to Deformation, Level ordering, Masses P. Möller et al., NPA 1992; ADNDT 1995, 1997; PRC2000

44. 107Zr Future Facility Reach(here ISF) 78Ni Critical region NSCL r-process campaign – MSU/Mainz/Notre Dame/Maryland Known before NSCL reach NSCL Experiments done • P. Hosmer, P. Santi, H. Schatz et al. • F. Montes, H. Schatz et al. • J.Pereira, K.-L.Kratz, A. Woehr et al.

45. The r-process abundances (observed in Solar System and Metal-Poor Stars) is the only clue that “he” left behind…for us • Initial conditions: r=29mg/cm3; T=1.5GK; n/seed = 92

46. Nuclear Physics in the r-process What Nuclear Physics ingredients are really important?

47. ETFSI-Q ETFSI-1 Mass number A=110 Z number r-process studies in two different regions of Terra Incognita Two r-process regions were explored: Ge-Br (56≤N≤60): lies in the region prior to the “weak” r-process. It could also constitute part of the seed r-process nuclei Y-Mo (A ≈110): lies right before the abundance trough prior to the A=130 peak (Pearson, et al. 1996) C.Freiburghaus et al., ApJ516 (1999) 381

48. Evolution of nuclear shape in two regions of Terra Incognita • Ge-Br (56≤N≤60): does the sudden onset of deformation (at N=60) persist “south” of 96Kr? • Y-Mo (A ≈110): are there more shape transitions between sudden onset of deformation at N=60 and closed shell at N=82 (new sub-shells?) • Nuclear shape evolution in these two regions will affect substantially the calculated masses andb-decay processes: strong impact in r-process calculated abundances R.F. Casten, Nucl. Phys. A443 (1985) 1 N. Schunck et al., Phys. Rev. C63 (2004) 061305(R) Nuclear Structure motivation • What do we want to measure? b-decay half-lives and Pn-values • Why? • They provide insight into nuclear structure in two “critical” r-process regions • Direct inputs in r-process calculations

49. Gross b-decay properties are sensitive to nuclear structure at different energy regimes Low energies Energies above Sn Gross b-decay properties used as nuclear structure probes Dobaczewski et al., PRL72 (1994) 981 B. Pfeiffer et al., NPA693 (2001) 282