Rich Opportunities for Astrophysics

Transcription

1 Rich Opportunities for Astrophysics A flood of new observations and more to come with INTEGRAL, JWST, Constellation-X, Growing computational capability Problems ripe for solution: How supernovae explode, how the heavy elements are formed, the nature of explosive burning on accreting neutron stars..(add your list). The challenge to nuclear physics Provide the fundamental information that governs stellar/galactic element formation, energy production, and chemical evolution. Ensure its incorporation in astrophysics models

2 Map onto the Nuclear Chart Need information from the neutron drip line to the proton drip line up to the heaviest nuclei Radioactive beams from present accelerators and from future accelerators such as RIA will be crucial to our success. Novae rp process p process Supernovae r process N-star crust processes protons neutrons

3 Supernovae and the r process Determination of r-process abundances-steady flow model Evolution of Fe core: pre-supernova and in collapse until formation of outgoing shock--affects the explosion process Neutrino process---spallation of abundant elements 7 Li, 11 B, 19 F, Modification of r-process abundances spallation of peak nuclides Neutrino oscillations Weak Strength in Astrophysics Detection of supernova neutrinos Evolution of accreting neutron stars

4 Typical (p,n) Spectrum Distribution of Weak Strength 90 Zr (p,n) 120 MeV 0 deg L = 1 GTGR IAS Allowed or Gamow- Teller transitions στ ± = Σ σ(ι)τ ± (i) L = 0, S = Τ = 1 Sum Rule: Σβ Σβ + = 3(N-Z) Giant resonance-gtgr Most strength (GT(L=0) and L=1) above IAS, obtain with hadronic charge exchange reactions. Strength near E=0, Important for r- and rp process. From β decay.

5 The r-process What is it? Heavy elements formed by rapid neutron capture on seed nuclei Flow along path near neutron drip line until (n,γ) = (γ,n) β β β β β Peak N(Z) t β After explosion, decay back to stable region. Where does it occur? Hot bubble In hot bubble just inside SN shock? Or in fusion of two neutron stars? This is seeming unlikely. Hot bubble

6 How were the Heavy Elements Made? r- and s-processes Rapid ( sec) and slow neutron capture Where r-? Supernovae? Neutron star mergers (improbable)? Dependences on nuclear properties: Masses Half-lives Delayed Neutron Emission Ratio Waiting Points (n,γ) (γ,n) Abundances Timescale Abundances

7 Generic r- Process Calculation Rapid Neutron Capture Process (r-process) relative abundance ν Processing ETFSIQ (shell quenching) ETFSI1 (no quenching) solar The Problem Problem: Nuclear physics or astrophysics model failure? Sensitivity to nuclear structure. Need to measure the important quantities. Understand the nuclear structure: Is there shell quenching (smaller shell gaps)? A Pfeiffer & Kratz, Mainz

8 The Principle First r-process Experiments at the NSCL Correlation of fragment implants and subsequent beta decays by pixelation of BCS PPAC Degrader neutron NERO Si detector ( E) Si BCS β Si Si Hosmer et al. (NSCL, Mainz, Maryland, Notre Dame, PPNL 4 cm x 4 cm active area 1 mm thick 40-strip pitch in x and y dimensions ->1600 pixels

9 Half-Lives Preliminary Analyses A=75-80, Hosmer, et al For some of these nuclei the fractions of β-delayed neutron emission will be obtained-not yet analyzed 117 Ru A = 115 to 124, Walters, Montes et al. 117 Ru, 119,120 Rh, 121 Pd, 124 Ag have yielded lifetimes to date.

10 Future r-process Studies at the NSCL r-process Pb Known halflife Fe Exp Hosmer et al. Exp Exp Approved expt NSCL/MSU Reach Montes, et al. Walters, et al. RIA will extend these measurements to the great majority of nuclei involved in the r-process

11 New Observations-- r-process stars New observations (Details Very old metal poor stars in galactic halo, extremely rich in r-process elements. Same distribution as in the solar system. Implies r-process is unique? (But distribution different for A<130, two processes?) U-Th clock Solar

12 RIA and the R Process RIA Reach Known Half-lives r-process NSCL Reach Next generation exotic beam facility in US In planning stage Would cover 80% of r-process path up to A=208 for at least a half-life measurement

13 Core-Collapse Supernovae Evolution of Massive Star Forms a growing56ni core When Mcore 1.4 Msun, can t be supported by e Core collapses Reaches r > nuclear density. Nuclei repel, core bounces. Outgoing shock wave forms electron pressure, ν s Blows off outer star:1051 ergs Stellar cool On on But, theoretical spherical SN Non-burning Non-b don t explode. Microphysics? H Fu H He C O Silicon Iron ( Fe )

14 Weak Processes in Supernovae Situation After silicon burning Fermi energy of e - allows capture into GT +.(T core 3.3 x 10 9 K, density 10 8 g/cm 3). At higher T, GT + thermally populated, β - decays back to ground state. EC and β - compete. Successive EC-β URCA process---ν emission, cools core GT + resonance strength dominates the processes (n,p) (p,n)

15 Measure GT + Strength--Hadronic Charge Exchange Principle (p,n) operator is similar in spin isospin to β decay operator B(GT) = σ CEX (q = 0)/σ unit σ unit depends on A Taddeuchi, NPA 469,125 Gamow Teller Accurary 5-10% Sufficiently high energy, > 120 MeV Effective interaction isolates S=T=1 Are some exceptions σuni t=

16 : FFN (IPM model) Present Situation (Caurier, et al NPA 653, 439(99 : data (n,p) (TRIUMF) : Caurier et al. (1999) SM : Caurier et al. folded with experimental resolution Quite good, some problems and what about unstable isotopes????

17 Supernovae-Sensitivity GT + Giant Resonance Compare rates Heger et al, Ap.J. 560 WW: Wallace-Weaver-IPM LMP: Large basis shell model: Langanke, Martinez- Pinedo, NPA 673 LMP rates give Smaller, lower entropy "Fe" pre-collapse core Larger homologous core More e-'s (Y e larger), lower T core. =>? Explosions easier 0.50 Y e Important nuclei Closer to stability than predicted earlier. Stable and radioactive nuclei important 15 M Fe 57 Co 10 5 * 53 Mn 59 Ni 57 Fe 61 Ni 56 Fe * 56 * Dominant Fe 53 Cr Stable 55 Mn Fe 53 Cr 57 Fe 10 2 Time till core collapse(sec) 10 1 WW LMP 53 Cr 10 0

18 Heavier Nuclei-Also Important and Unstudied Heavier nuclei are important during collapse (A=60-120) Langanke et al PRL Previously ignored: In IPM transitions are Pauli blocked for Z<40, N>40. But in nature: configuration mixing and thermal excitation relieve blocking. Results: Langanke, et al. : nuclei (previously unimportant) dominate electron capture by x10 over protons Changes nature of core (Hix, et al.) : Mass behind shock (-20%), central density (-10%), ν luminosity (+15%), average ν energy (+1 MeV)

19 First expts Secondary triton beams 10 6 /sec at MSU/NSCL, 120 MeV/A tritons (Daito et al). Resol: 160 kev achieved Preliminary data on 58 Ni Near Future (Zegers, et al.) 10 7 /sec secondary beams CH2, 24 Mg, 50 V, 53 Cr, 74 Ge, 94 Mo (t, 3 He) Option Comments E(MeV) Pros: Unique beam-spectrometer(s800), simple analysis, calibration available from ( 3 He, t) reaction at Osaka. Con: More beam nice though not essential. C o u n t s MeV MeV kev 230 kev Sherrill, et al 4.5 MeV MeV MeV MeV 1-12 C(t, 3 He) 12 B Θ lab =0 o 1.7 o 12 C(t, 3 He) 12 B Θ = o lab o

20 Preliminary results on 58 Ni Expt l detail or two E t =350 MeV, I = 10 6 /sec. 24 hour run. (Future: >10x more beam) E t = 3.5 MeV, dispersion matched spectrometer (S800) gives 0.16 MeV Comments The results of preliminary analysis are inconsistent with the TRIUMF (n,p) data. A similar inconsistency has been found in 85 MeV/nucleon (d, 2 He) data at KVI

21 Radioactive Nuclei--General Approach No targets Inverse kinematics 3 H Ni Co Focal Plane 3 He Problems: Outgoing light particle charged, has very low energy, won t escape from practical target. Tritium target. Solution: Detect heavy particle in S800 at 0 deg. A general solution. S800 Target Superconducting Magnets Bρ = 4.2 Tm 5% p, 20 msr Expected resolution 1 MeV

22 (d, 2 He) in Inverse Kinematics Other Possibilities Pros: Outgoing protons allow thicker targets, maybe pure 2 H (cryogenic). Can completely characterize final state. Cons: Complicated detections scheme (large Ω, good resolution); simulations (R. Zegers)look promising, not yet complete. Will be hard to get sub-mev resolution. (p,n) Inverse Kinematics Good resolution with a highly granular neutron detector Well understood reaction model Test models for GT, forbidden strength T <, T 0,{T >?} states) ( 7 Li, 7 Be) Inverse Kinematics. Complex--need to detect decay gamma from 7 Be(0.431, 3/2 - ) to guarantee S = 1?? If so, lose efficiency. A first experiment, now under analysis, has been carried out on 56 Ni.

23 Weak Interactions in the Neutron Star Crust Explosive H-burning--neutron star surface. Deposits heavy ashes on surface Electron capture processes material to n-rich Ni (28) 56 Ni border known masses Si (14) Mg (12) Ne H,He Ar (18) S (16) Ca (20) Ti (22) Cr (24) Fe (26) αp/rp αp/rpprocess process g/cm 3 ) Electron capture capture 10 9 g/cm 3 ) 34 Ne 56 Ar and so on g/cm 3 ) Electron capture capture and and n-emission Pyconuclear fusion fusion 68 Ca NSCL Reach

24 Joint Institute for Nuclear Astrophysics (JINA) a new NSF Physics Frontiers Center Identify and address the critical open questions and needs of the field Form an intellectual center for the field Overcome boundaries between astrophysics and nuclear physics and between theory and experiment Attract and educate young people Nuclear Physics Experiments Astronomical Observations Astrophysical Models Nuclear Theory Core institutions: Notre Dame MSU/NSCL U. of Chicago Associated: SciDAC SSC LLNL, UCSC, LANL U. of Arizona UC Santa Barbara ANL

25 Virtual Journal of Nuclear Astrophysics Articles from 30 journals, appears weekly:

26 JINA Web Page---

27 National Superconducting Cyclotron Laboratory Biomedical & Physical Sciences Biochemistry Chemistry NSCL

28 Experimental Areas Test 4Pi Scat. Cham. Sweeper Trap RPMS n-ball S msr E/E = 10-4

29 Beam Production at NSCL/CCP A1900 Properties Bρ = 6 Tesla-m p/p = ±2.5% dω = 8 msr

30 NSCL S800 Spectrometer Dipole Dipole Properties dω = 20 msr (7 o x10 o ) E/E = 10-4

31 Fast Beams from the NSCL CCP