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Professor Dr. Norbert Pietralla TU Darmstadt
Nuclear Structure Physics at 4GLS
Norbert Pietralla
Institut für Kernphysik
Darmstadt University of Technology
TUD
Collaborative Research CenterSFB634
Research Center of ExcellenceNuclear and Radiation Physics
TUD
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Professor Dr. Norbert Pietralla TU Darmstadt
Vision of Nuclear Physics
Understanding the properties of heavy atomic nuclei from their basic constituents, quarks and gluons, and from the interactions between them.
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Professor Dr. Norbert Pietralla TU Darmstadt
Relevance Deductive understanding of Nature
Solid understanding of the nucleus as a laboratory for other fields (standard model, neutrino physics, strongly interacting many-body Fermi-systems…)
Dynamics of cosmic objects and the “Origin of the Elements“ (astrophysics, nuclear astrophysics)
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Professor Dr. Norbert Pietralla TU Darmstadt
Recent Progress Systematic derivation of structural form of
nucleon-nucleon interaction from QCD in Chiral Perturbation Theory
Unique low-energy NN-potential Vlow-k from Renormalization Group approach
Non-perturbative all-order calculations from self-consistent iteration methods for nuclear many-body systems
Advanced many-body techniques, e.g., No-Core Shell Model, Monte-Carlo Shell Model,…
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Professor Dr. Norbert Pietralla TU Darmstadt
shell structure:valence nucleons
Cooper pairing:N s,d boson system
Collective motion:nuclear shapes
Once the atomic nucleus is formed effective (in-medium) forces can generate simple pattern.
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Professor Dr. Norbert Pietralla TU Darmstadt
Outline
Nuclear physics with low-energy photons (nuclear dipole physics)
Impact of photon beams from Laser Compton Backscattering
Recent progress at Duke‘s HIS
Research potential of -ray beams from Laser Compton Backscattering
Summary
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Professor Dr. Norbert Pietralla TU Darmstadt
Nuclear Structure Physics with low-energy photon beams Pure EM-interaction
(nuclear-) model independent“small“ cross sections, thick targets
Minimum projectile mass
min. angular momentum transfer, spin-selective: dipole-modes
Polarisation
“Parity physics“
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Professor Dr. Norbert Pietralla TU Darmstadt
Nucleon-Spin-flip
Role of Isovector Spin-flip M1 excitations in Nuclear Physics
E(MeV)
Quark-Spin-flip
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Professor Dr. Norbert Pietralla TU Darmstadt
Electric Giant Dipol Resonance (GDR)
Protons Neutrons
Sensitive to average Proton-Neutron-Restoring Force
but insensitive to shell structure: need low-energy E1/M1 data !
GDR in 197Au
GDR-Strength vs A
Data from: A.Bohr, B.Mottelson “Nuclear Structure”
E1
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Professor Dr. Norbert Pietralla TU Darmstadt
Photonuclear Reactions
gs
´
Separationthreshold
AX
A´Y Nuclear Resonance Fluorescence (NRF)PhotoactivationPhotodesintegration
Absorption
(-activation)
´
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Professor Dr. Norbert Pietralla TU Darmstadt
Traditionally Bremsstrahlung: Kneissl,Pietralla,Zilges, J.Phys.G 32, R217 (2006).
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Professor Dr. Norbert Pietralla TU Darmstadt
Overview: dipole modes
Exotic Modes
B(M1)
Orbital M1 StrengthScissors mode,…
Spin M1 Strength
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Professor Dr. Norbert Pietralla TU Darmstadt
Scissors Mode in Deformed Nuclei (Darmstadt, 1983)
Bohle et al., NPA 458, 205 (1986).
Scissors mode
classically: current loop => M1
magnetic dipole excitation
electron scattering
photon scattering
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Professor Dr. Norbert Pietralla TU Darmstadt
S-DALINAC facility at IKP TU Darmstadt
12
i
1
2
Photon Experiments
10 MeV Injector: Photon Scattering / Photofission
< 30 MeV Tagger: Photodesintegration / Photon Scattering
Source
130 MeV Electron LINAC
Electron Source
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Professor Dr. Norbert Pietralla TU Darmstadt
Darmstadt Low-Energy Photon Scattering Site at S-DALINAC
Target
Ge(HP)
-detectors
Radiator targete-
Energie
Inte
ns
ity Electrons
Energie
Inte
ns
ity Bremsstrahlung
< 10 MeVCu
A.ZilgesE < 10 MeV
Cu
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Professor Dr. Norbert Pietralla TU Darmstadt
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Professor Dr. Norbert Pietralla TU Darmstadt
A. Zilges et al., PLB 542 (2002) 43. S. Volz et al., NPA 779 (2006) 1.A. Zilges, contrib. to Vico Equense 07.
Systematics of the Pygmy Dipole Resonance
• Concentration around 5-7 MeV
• Strong fragmentation
• Summed strength: Scaling with N/Z ?Is this really all E1 strength ?
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Professor Dr. Norbert Pietralla TU Darmstadt
Parity Measurements
Principle of a
Compton-Polarimeter
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Professor Dr. Norbert Pietralla TU Darmstadt
Modest polarisation sensitivity
Better use polarized -ray beams !
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Professor Dr. Norbert Pietralla TU Darmstadt
Azimuthal asymmetry → parity quantum no.
Parity Measurements with Linearly Polarized Photon Beams
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Professor Dr. Norbert Pietralla TU Darmstadt
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Professor Dr. Norbert Pietralla TU Darmstadt
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Professor Dr. Norbert Pietralla TU Darmstadt
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Professor Dr. Norbert Pietralla TU Darmstadt
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Professor Dr. Norbert Pietralla TU Darmstadt
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Professor Dr. Norbert Pietralla TU Darmstadt
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Professor Dr. Norbert Pietralla TU Darmstadt
HIgS Beam Profile
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Professor Dr. Norbert Pietralla TU Darmstadt
Testing shell structure from M1 Spin-flip excitation
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Professor Dr. Norbert Pietralla TU Darmstadt
40Ar
First ever observation of a 1+ state of 40Ar
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Professor Dr. Norbert Pietralla TU Darmstadt
T.C.Li, NP et al, Phys.Rev.C (2006).
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Professor Dr. Norbert Pietralla TU Darmstadt
Astrophysical Relevance of M1 Data
Darmstadt data 54Fe
Langanke et al., PRL (2004).Neutrino-cross sections
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Professor Dr. Norbert Pietralla TU Darmstadt
Direct Measurement of B(GT) from Charge-Exchange Reactions
Osaka-data
Fujita et al., PRL(2005).Adachi et al.,PRC (2006).
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Professor Dr. Norbert Pietralla TU Darmstadt
Polarization in the entrance channel
• Linear polarization (HIS)spin/parity program (since 2001)
• Circular polarization (HIS, S-DALINAC)parity non-conservation
20Ne, 238U
E
bremsstrahlungspectrum N
P ≤ 75%
e-target
circular
bremstarget
-θ θForward-backwardasymmetry ?
Parity-violation
Weak interaction
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Professor Dr. Norbert Pietralla TU Darmstadt
The 20Ne case: parity mixing of yrast levels
ΔE=7.5±5.7 keV
“enhancement factor”670 ± 7000
Γ(1-) ≤ 0.3 keV
Γ(1+) ?
T<=0
1+
1-
11270±5
11262±3
20Ne
0+
20F, T< = 1
1- 1+
3+ 4+
5+
2+
(d5/21)(d5/2
3)
gs
T=1isobaric analog states
Goal: measure parity violation in simple states !
Understand effects of weak interactionmicroscopically
► e.g., study the parity doublet in 20Ne !
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Professor Dr. Norbert Pietralla TU Darmstadt
Heavy Atomic nucleus
• many-body system
• consists of two equivalent entities (protons-neutrons)
• quantum system
• COLLECTIVITY
• SHELL STRUCTURE
• ISOSPIN SYMMETRY
Two-fluid quantum system
Generic Aspects of Nuclear Structure
Coexist, interplay, and compete?
Study collective proton-neutron valence shell excitations !
(combine all 3 aspects)
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Professor Dr. Norbert Pietralla TU Darmstadt
Themes and challenges of Modern Science
•Complexity out of simplicity
How the world, with all its apparent complexity and diversity can be
constructed out of a few elementary building blocks and their interactions
•Simplicity out of complexity
How the world of complex systems can display such astonishing regularity
and simplicity
•Understanding the nature of the physical universe
•Manipulating nature for the benefit of mankind
Nuclei: Two-fluid, many-body, strongly-interacting, quantal systems provide wonderful laboratories for frontier research in all four areas
From US-NSAC-charge: “Nuclear Physics with the Rare Isotope Accelerator”
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Professor Dr. Norbert Pietralla TU Darmstadt
Summary
Nuclear structure physics with -ray beams is a vivid field with high discovery potential
4GLS can become a major facility in this field Needs: - energy-tunable, high-flux, polarized -
ray beam from LASER-Compton backscattering All this is possible at 4GLS !
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Professor Dr. Norbert Pietralla TU Darmstadt