120 likes | 138 Views
Structure and astrophysics from nuclear reactions with exotic nuclei July 14, 2009, University of the West of Scotland (Paisley Campus). Questions that drive the field: How to unify structure and reaction aspects of nuclei?
E N D
Structure and astrophysics from nuclear reactions with exotic nuclei July 14, 2009, University of the West of Scotland (Paisley Campus) • Questions that drive the field: • How to unify structure and reaction aspects of nuclei? • How to incorporate open-channels effects into microscopic nuclear structure models? • How to incorporate microscopic structure information into reaction models? • What is the reliability of nuclear structure/astrophysics data extracted in a model dependent way from reaction measurements? How can we minimize the “model” aspect? • What is the preferred strategy for developing the microscopic reaction theory? Can large computers help? • Crucial Questions: • What is the essential input for developing the “universal” optical model potential? • How to take consistently into account breakup and transfer channels? Do we need more data at this point? • How far can surrogate reactions take us? Is (d,p) going to inform us about (n,g)? • How are cluster configurations born in nuclei? What is the microscopic foundation of the Ikeda diagram? • What is the interplay between continuum and isospin-breaking effects? • Can threshold effects be used as spectroscopic tools?
(7.27) (14.44) (19.17) (28.48) (7.16) (11.89) (21.21) (14.05) (4.73) Excitation energy (13.93) (9.32) 11Li Mass number
Physics of rare isotopes Interactions Many-body Correlations Open Channels • Interactions • Isovector (N-Z) effects • Poorly-known components come into play • Long isotopic chains crucial • Configuration interaction • Mean-field concept often questionable • Asymmetry of proton and neutron Fermi surfaces gives rise to new couplings (Intruders and the islands of inversion) • New collective modes; polarization effects • Open channels • Nuclei are open quantum systems • Exotic nuclei have low-energy decay thresholds • Coupling to the continuum important • Virtual scattering • Unbound states • Impact on in-medium Interactions
Hagen et al, ORNL/UTK Ab initio: Reactions Nollett et al, ANL Coupled Clusters n+ CC GFMC Quaglioni & Navratil, LLNL 2008 No Core Shell Model + Resonating Group Method Overlap functions provide the link!
n-10Be phase shifts with CD-Bonn NN interaction 10Be n 11Be: Quaglioni and Navratil, Phys. Rev. C 79, 044606 (2009) n-10Be phase shifts • NCSM/RGM calculation: • CD-Bonn 2000 NN potential • two-body effective interaction Nmax=7 @ h= 13 MeV • 10Be states: • n-10Be wave function extends to large distances • Relative kinetic energies decrease • Dramatic increase of 11Be binding energy 3.0 2.5 2.0 1.5 1.0 0.5 0.0 -0.5 -1.0 E [MeV] • Inversion between andstates reproduced 1/2- 1/2+ Expt. NCSM/RGM NCSM The proper description of extended n-10Be configurations leads to parity-inverted 11Be g.s.
Reactions Workflow UNEDF Reaction Work Ground state Excited states Continuum states Target A = (N,Z) Structure ModelsMethods: HF, DFT, RPA, CI, CC, … Transition Density [Nobre] KEY: UNEDF Ab-initio Input User Inputs/Outputs Exchanged Data Related research UNEDF: VNN, VNNN… Transition Densities Veff for scattering Folding [Escher, Nobre] Eprojectile Transition Potentials Deliverables Coupled Channels or DWBA[Thompson, Summers] Hauser- Feshbach decay chains [Ormand] Partial Fusion Theory [Thompson] Residues (N’,Z’) Inelastic production Compound emission Two-step Optical Potential Elastic S-matrix elements or Resonance Averaging [Arbanas] Neutron escape [Summers, Thompson] Preequilibrium emission Voptical Global optical potentials Optical Potential [Arbanas]
HRIBF experiments to understand the 26Al(p,g)27Si stellar reaction rate • Large amounts of 26Al have been observed in the Galaxy by g-ray telescopes. • The nucleosynthesis must be ongoing since the half-life is much shorter than the age of the Galaxy. • Source of 26Al is unknown. Most probable source is supernovae but novae also contribute. COMPTEL Studied mirror levels with 26Al(d,p)27Al First measurement of the 26Al(p,p)26Al excitation function
Conclusions • Much excitement in the air • Low-energy reactions are difficult • Low-energy reactions with exotic nuclei are very difficult (low-lying thresholds) • Developing microscopic optical model is a key challenge • Exciting theoretical developments • Complex-energy shell model and SMEC provide unification, predict new phenomena, and will soon provide quantitative guidance • CDCC becomes more sophisticated (3-body continuum incorporated) • Other approaches, e.g., ADWA, very useful • Ab-initio approaches • Time-dependent approaches • Spectroscopic factors have been overrated. The overlap amplitude provides a link between structure and reactions. • What astrophysical reactions are crucial? Need for sensitivity studies. • Unique, and sometimes spectacular, data from RNB facilities provide important insights, but… • More quality theory needed • Exclusive data important to calibrate models, but… • More selectivity is needed