Nuclear astrophysics

1. Where did this come from? log (abundance) Mass Nuclear astrophysics A survey in 3 acts Jeff Blackmon, Physics Division, ORNL Act II - Stellar obituary • Stellar evolution • s process • Supernovae • r process

2. Stellar Classification Aldebaran Betelgeuse Alnitak Rigel Sirius Arneb

3. Core H2 exhausts H burn CO core He burn Stellar evolution Globular cluster Most stars formed at about the same time AGB Brighter He burning Asymptotic Giant Branch Star Giant branch H-shell burning Convective envelope Cooler

4. Numerous complementary techniques 12C(p,p’)12C* 13C(3He,)12C* , 3, e+e- He burning & the “Hoyle” state t1/2(8Be)=9.7x10-17 s 8Be  0+ 7.654 7.367 8Be+ e+e- 0+ resonance near the Gamow energy was predicted by Hoyle Phys Rev 92 (1953) 1095. 4.439 2+ 0+ 12C Largest uncertainty ee~12% Experiments now at West. Mich. U.

5. New Stuttgart measurements: improvement? 12C(,)16O - the “holy grail” ? Ecm The 12C(,)16O reaction rate fixes the ratio of 12C/16O in the core The 12C/16O ratio substantially affects the subsequent evolution of the star: Size of Fe coreSupernova? Influence of subthreshold states substantial uncertainties in extrapolation 16O Kunz et al., PRL (2001) = 0.1 fb 300 keV

6.   New WNSL Measurement France et al., PRC 75 (2007) 065802. Approach @ ANL (Tang et al.) 12C(,)16O - via 16N  decay Azuma et al. PRC 50 (1994) Ecm 16N 12C 16O

7. 12C(,)16O via ANC • A nucleon or “cluster” of nucleons (no internal degrees of freedom) is transferred from one nucleus to another. • The core nuclei are unperturbed. exp=S1S2DWBA

8. 12C 16O 12C(,)16O via ANC SubCoulomb  transfer to subthreshold states Brune et al. PRL 83 (1999) 6.92 (2+) 7.12 (1-) C2(2+)=(1.30.2) x 1010 fm-1 C2(1-)=(4.30.8) x 1028 fm-1 DWBA w/ 16N  decay

9. Neutron sources in AGB Stars Stars are thermally unstable: mixing, convection, mass loss 12C(p,g)13N(bn)13C(a,n)16O 22Ne(n)25Mg Flash convective envelope driven off H envelope radius mixing 13C(,n) 13C(,n) Convective pocket He intershell CO core CO core (white dwarf) time

10. r process • ~ 70% of isotopes • Far from stability • See supernovae • p process ~ 10% of isotopes • Very low abundance • Secondary process • Neglected here constant Synthesis of heavy elements • s process • ~ 80% of isotopes • (n,g) rates needed • Branch points crucial (s-wave)

11. log (abundance) Mass Recipe for untangling r & s abundances Calculate s process yields and fit to s only isotopes Subtract s abundances from solar system to get r abundances

12. Stardust in a haystack Tiny grains isolated from meteorites Unusual grains identified with SIMS Nittler, Earth Planetary Sci Lett (2003) Nguyen & Zinner, Science 303 (2004) 1496. Some grains have preserved isotopic composition from solar environment (XNd/144Nd)/(solar) Relative abundances for isotopes of a given element from a single AGB star Guber et al.

13. (n,) cross sections for the s process Good data on most stable isotopes Spallation n sources TOF techniques Good energy resolution Often high level densities ORELA • Major outstanding issues • Influence of low-energy levels on <v> at low temp • Effect of thermal excitations in stellar environment • Branch point isotopes

14. The new frontier Experiments now possible with samples of only ~ 1016 atoms/cm2. Important s process branch points status feasible High efficiency detector arrays High segmentation to handle rate from radioactive sources DANCE

15. r process • ~ 70% of isotopes • Far from stability • See supernovae • p process ~ 10% of isotopes • Very low abundance • Secondary process • Neglected here constant Synthesis of heavy elements • s process • ~ 80% of isotopes • (n,g) rates needed • Branch points crucial

16. The r process site Galactic chemical evolution arguments favor supernovae as the dominant source for elements early in the history of the Galaxy  an r process Argast et al., A&A 416 (2004) 997.

17. Cowan & Sneden, Nature 440 (2006) 1151. Frebel et al., Nature 434 (2005) 871. Fe/H < 10-5solar Creation of elements in the early Galaxy Now many observations of unmixed supernova nucleosynthesis in the Galactic halo • CS22892-052 • Fe/H = (8x10-4)solar = very old • r/Fe = 50 solar • Only 2 known in 2000 • Now extensive surveys • e.g. see Frebel et al., ApJ 652 (2006) 1585 • SEGUE (Sloan DSS) • Spectra of >2x105 selected halo stars • Expect ~ 1% with Fe/H < 0.001solar • ~36 known r process stars • 11 with r/Fe > 10 solar • Distribution Fe/H puzzling • Lowest Fe/H stars intriguing Z>55 pattern matches solar CS22892 (C&S, Nature 440) Z<50 abundances vary

18. Anatomy of a supernovae • Fermi degeneracy initially supports core • Shell Si burning increases core size of • Electron capture on nuclei in core begins to reduce pressure support • Core undergoes runaway collapse • Reaches supernuclear densities & shock rebounds -- EOS important • Mechanism involves interplay of hydrodynamics and nuclear physics • Spherical models fail to explode • Multidimensional effects are critical • Stars > 10 solar masses • Higher gravity • Faster burning stages • Less mass loss • C burning • O burning • Si burning Lecture 3 In rapid succession Standing Accretion Shock Instability

19. History of SN1987a

21. Nucleosynthesis sites in supernovae Environment above neutron star is likely site for the r process Fe group nuclei produced from nuclear statistical equilibrium

22. Abundaces relative to solar • with n reactions • without n reaction Influence of weak interaction Effect of e-capture rates on formation of the shock • Electron capture rates affect the formation of the shock wave. • Neutrino interactions play a role in driving the explosion. • Neutrino induced reactions alter nucleosynthesis. • Weak rates in this mass region are not well understood: • GT strength distributions • first-forbidden contribution Fröhlich et al., PRL 96 (2006)

23. Cole et al., PRC 74 (2006) 034333. Charge exchange reactions with fast beams at the NSCL Charge exchange reactionssuch as (t,3He) are sensitiveprobes for GT strength at 100 – 200 MeV/u • Needed for • core collapse supernova models • type Ia supernova models • neutron star crust processes Special case or systematic issue? Need systematic measurements for entire relevant range(especially beyond fp shell where nuclear models become much simpler) • can help decide which theoretical model to use and can help to improve theoretical models for supernova usage • Need to develop technique for inverse kinematics and radioactive beams

24. nm nm SNS neutrino spectrum ne http://www.phy.ornl.gov/nusns nSNS • A proposal has been submitted to DOE to construct a facility for neutrino reaction measurements at the Spallation Neutron Source. BL18 ARCS GeV protons Segmented Detector Proton beam (RTBT) Accumulator Homogeneous Det. Hg target ne+OF+e- (450 events/yr) ne+FeCo+e- (1100 events/yr) ne+AlSi+e- (1100 events/yr) ne+Pb Bi+e- (4900 events/yr) Likely initial program

25. Only masses, t1/2, and Pn needed Cartoon r process Small Sn (g,n) >> (n,g) >> t1/2 Large Sn (n,g) >> (g,n) >> t1/2 • Free parameters nn, kT, t • Instantaneous freezeout & decay to stability

26. Calculated r process

27. Fission? (Qian & Wasserburg) Astrophysical environment? Freezeout effects? Masses? Results of r process calculations • Many different n densities needed • Reasonable fits to A=130,190 peaks • Not so nice reproduction of intermediate nuclei Evidence for quenching of the shell gaps?(Kratz et al.)

28. P. Hosmer et al. PRL 94 (2005) 112501. NSCL fast beam r-process campaign: the half-life of 78Ni t1/2(78Ni): 110 +100-60 ms 3He + n -> t + p Effect of new t1/2 on r process abundances neutron r-process beam Si stack ~ 100 MeV/u NERO Particle identification in rare isotope beam Shorter 78Ni half-life leads to greater production of A=190 peak 78Ni The properties of neutron-rich nuclei are crucial for understanding the site(s) of the r process and the chemical history of the Galaxy Half-life of 78Ni measured with 11 events.

29. Mass measurements • Large number of isotopes circulate and are measured in ring Matos, Ph.D. Univ. Giessen Yu. Litvinov et al., NPA756 (2005) 3. • 2 modes: • Schottky - slow, more precise • isochronous - fast, less precise Measurements now crossing into regime of light r process

30. The Chart of the Nuclides http://www.nndc.bnl.gov/chart/

31. = half-life measurements since 2000 (6th ed.) The Chart of the Nuclides http://www.nndc.bnl.gov/chart/ (neutron-rich nuclei only)

32. = half-life measurements since 2000 (6th ed.) The Chart of the Nuclides http://www.nndc.bnl.gov/chart/ r process (neutron-rich nuclei only) Only a few measurements in r process path

33. Dillman et al., PRL 91 (2003) 162503. Radford et al., PRL 88 (2002) 222501. Varner et al., EPJ 25 (2005) 391. 132Sn(d,p)133Sn @ HRIBF 3p3/2 Jones et al. Preliminary 2f7/2 3p1/2? HRIBF 2f5/2 EP (channels) Ex Structure n-rich nuclei and the r process Masses, half-lives and Pn are crucial direct impact on r process abundances. Must rely on theory. Properties like level energies and B(E2) values provide some direct benchmarks. Understanding the structure of neutron-rich nuclei is crucial to improving extrapolations to more neutron-rich (unmeasured nuclei).

34. The HRIBF

35. Intense 252Cf fission source under construction at ATLAS • Gas stopping technology • Neutron-rich RIBs will push the boundaries of our knowledge • Different region on nuclei complementary to HRIBF CARIBU CPT measurements of very neutron-rich nuclei Intense beams and high energy will allow unique structure studies, e.g. (p,t)

36. Next-generation RIB Facilities RIBF (RIKEN), FAIR (GSI), SPIRAL-II (GANIL), RIA (USA) Atomic number (Z) Ground state properties of nearly all r process nuclei up to the A=190 peak can be measured Nuclear structure studies far from stability will greatly improve our ability to extrapolate to the unknown Neutron number (Z) Atomic number (Z) Understanding observations of the oldest stars and the origin of the heavy elements in our Galaxy Neutron number (Z)