1. Nuclear Structure Physics at 4GLS
Norbert Pietralla
Institut für Kernphysik
Darmstadt
University of Technology
TUD
Collaborative Research Center
SFB634
Research Center of Excellence
Nuclear and Radiation Physics
TUD
Professor Dr. Norbert Pietralla TU Darmstadt

2. Vision of Nuclear Physics
Understanding the properties of heavy atomic nuclei from their basic constituents, quarks and gluons, and from the interactions between them.
Professor Dr. Norbert Pietralla TU Darmstadt

3. 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)
Professor Dr. Norbert Pietralla TU Darmstadt

4. 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,…
Professor Dr. Norbert Pietralla TU Darmstadt

5. Professor Dr. Norbert Pietralla TU Darmstadt
Once the atomic nucleus is formed effective (in-medium) forces
can generate simple pattern.
shell structure:
valence nucleons
Cooper pairing:
N s,d boson system
Collective motion:
nuclear shapes
Professor Dr. Norbert Pietralla TU Darmstadt

6. 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 HIS
Research potential of -ray beams from Laser Compton Backscattering
Summary
Professor Dr. Norbert Pietralla TU Darmstadt

7. 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“
Professor Dr. Norbert Pietralla TU Darmstadt

8. Role of Isovector Spin-flip M1 excitations in Nuclear Physics
(MeV)
Nucleon-Spin-flip
Quark-Spin-flip
Professor Dr. Norbert Pietralla TU Darmstadt

9. Electric Giant Dipol Resonance (GDR)
Protons
Neutrons E1
GDR in 197Au
GDR-Strength vs A
Sensitive to average Proton-Neutron-Restoring Force
but insensitive to shell structure: need low-energy E1/M1 data !
Professor Dr. Norbert Pietralla TU Darmstadt
Data from: A.Bohr, B.Mottelson “Nuclear Structure”

10. Photonuclear Reactions
Separation
threshold
Absorption ´  ´ 
A´Y  gs AX
Nuclear Resonance Fluorescence (NRF)
Photoactivation
Photodesintegration
(-activation)
Professor Dr. Norbert Pietralla TU Darmstadt

11. Professor Dr. Norbert Pietralla TU Darmstadt
Traditionally Bremsstrahlung: Kneissl,Pietralla,Zilges, J.Phys.G 32, R217 (2006).
Professor Dr. Norbert Pietralla TU Darmstadt

12. Overview: dipole modes
Spin M1 Strength
Exotic Modes
Orbital M1 Strength
Scissors mode,…
B(M1)
Professor Dr. Norbert Pietralla TU Darmstadt

13. Scissors Mode in Deformed Nuclei (Darmstadt, 1983)
classically: current loop => M1
magnetic dipole excitation
electron scattering
photon scattering
Bohle et al., NPA 458, 205 (1986).
Professor Dr. Norbert Pietralla TU Darmstadt

14. M1 phenomena in the nuclear valence shell
Collectivity of the Scissors Mode
Richter,
Kneissl,
von Brentano
et al.
Stuttgart-Darmstadt-Köln
Measure of quadrupole
collectivity 1+ 2+ E2 M1
N. Pietralla et al., PRC 58, 184 (1998)
Professor Dr. Norbert Pietralla TU Darmstadt

15. S-DALINAC facility at IKP TU Darmstadt1 2 i 1 2
Photon Experiments
10 MeV Injector: Photon Scattering / Photofission
< 30 MeV Tagger: Photodesintegration / Photon Scattering
Source
130 MeV Electron LINAC
Electron Source
Professor Dr. Norbert Pietralla TU Darmstadt

16. Darmstadt Low-Energy Photon Scattering Site at S-DALINAC
A.Zilges
E < 10 MeV
Target
Ge(HP)
g-detectors
Radiator target e- g
Energie
Intensity
Electrons
Bremsstrahlung Cu Cu
< 10 MeV
Professor Dr. Norbert Pietralla TU Darmstadt

17. Professor Dr. Norbert Pietralla TU Darmstadt

18. Is this really all E1 strength ?
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 ?
A. Zilges et al., PLB 542 (2002) 43.
S. Volz et al., NPA 779 (2006) 1.
A. Zilges, contrib. to Vico Equense 07.
Professor Dr. Norbert Pietralla TU Darmstadt

19. Professor Dr. Norbert Pietralla TU Darmstadt
Parity Measurements
Principle of a
Compton-Polarimeter
Professor Dr. Norbert Pietralla TU Darmstadt

20. Modest polarisation sensitivity Better use polarized -ray beams !
Professor Dr. Norbert Pietralla TU Darmstadt

21. Parity Measurements with Linearly Polarized Photon Beams
Azimuthal asymmetry → parity quantum no.
Professor Dr. Norbert Pietralla TU Darmstadt

22. Professor Dr. Norbert Pietralla TU Darmstadt

23. Professor Dr. Norbert Pietralla TU Darmstadt

24. Professor Dr. Norbert Pietralla TU Darmstadt

25. Professor Dr. Norbert Pietralla TU Darmstadt

26. Professor Dr. Norbert Pietralla TU Darmstadt

27. Professor Dr. Norbert Pietralla TU Darmstadt

28. Professor Dr. Norbert Pietralla TU Darmstadt
HIgS Beam Profile
Professor Dr. Norbert Pietralla TU Darmstadt

29. Testing shell structure from M1 Spin-flip excitation
Professor Dr. Norbert Pietralla TU Darmstadt

30. Professor Dr. Norbert Pietralla TU Darmstadt

31. First ever observation of a 1+ state of 40Ar
Professor Dr. Norbert Pietralla TU Darmstadt

32. Professor Dr. Norbert Pietralla TU Darmstadt
Duke-Stony Brook expt.
high-pressure Ar gas
HIgS polarized g-beam
7.7 MeV < E < 11 MeV
analyzing power 50%
Duke – Stony Brook data (2 examples)
Professor Dr. Norbert Pietralla TU Darmstadt

33. Professor Dr. Norbert Pietralla TU Darmstadt
T.C.Li, NP et al, Phys.Rev.C (2006).
Professor Dr. Norbert Pietralla TU Darmstadt

34. Astrophysical Relevance of M1 Data
Langanke et al., PRL (2004).
Neutrino-cross sections
Darmstadt data
54Fe
Professor Dr. Norbert Pietralla TU Darmstadt

35. 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).
Professor Dr. Norbert Pietralla TU Darmstadt

36. 250 keV Thermionic Electron Gun
Polarized Beams
100 keV Polarized Electron Gun
250 keV Thermionic Electron Gun
10 MeV Injector
To Experimental Hall
5 m
Spatial restriction – transport of accelerator equipment
Professor Dr. Norbert Pietralla TU Darmstadt

37. S-DALINAC Polarized INjector (SPIN)
Preparation system
Polarized electron gun
Differential pumping stages
Injector cryostat
Prebuncher system
Chopper
Mott polarimeter
Wien filter
1 m
Red Hall Entrance
Thermionic electron gun
Injector cryostat
2 m
From Gun Laser
Design of polarized injector beam line finished
(Prof.Dr.J.Enders)
Installation begins – middle of 2007
Professor Dr. Norbert Pietralla TU Darmstadt

38. Polarization in the entrance channel
Linear polarization (HIS)
spin/parity program (since 2001)
Circular polarization (HIS, S-DALINAC)
parity non-conservation
20Ne, 238U
bremstarget
target e- g
Forward-backward
asymmetry ?
Parity-violation
Weak interaction
circular -θ θ Eg
bremsstrahlung
spectrum Ng
Pg ≤ 75%
Professor Dr. Norbert Pietralla TU Darmstadt

39. The 20Ne case: parity mixing of yrast levels
20F, T< = 1 1- 1+ 3+ 4+ 5+ 2+
p(d5/21)n(d5/23) gs
ΔE=7.5±5.7 keV
“enhancement factor”
670 ± 7000
Γ(1-) ≤ 0.3 keV
Γ(1+) ? 1+ 1-
11270±5
11262±3
20Ne 0+
T=1
isobaric analog states
Goal: measure parity violation
in simple states !
Understand effects of weak interaction
microscopically
► e.g., study the parity doublet in 20Ne !
T<=0
Professor Dr. Norbert Pietralla TU Darmstadt

40. Generic Aspects of Nuclear Structure
Heavy Atomic nucleus
Two-fluid quantum system
many-body system
COLLECTIVITY
quantum system
SHELL STRUCTURE
consists of two equivalent entities (protons-neutrons)
ISOSPIN SYMMETRY
Coexist, interplay, and compete?
Study collective proton-neutron valence shell excitations !
(combine all 3 aspects)
Professor Dr. Norbert Pietralla TU Darmstadt

41. Professor Dr. Norbert Pietralla TU Darmstadt
From US-NSAC-charge: “Nuclear Physics with the Rare Isotope Accelerator”
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
Professor Dr. Norbert Pietralla TU Darmstadt

42. 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 !
Professor Dr. Norbert Pietralla TU Darmstadt

43. Professor Dr. Norbert Pietralla TU Darmstadt

44. Die Valenz-Proton-Neutron Wechselwirkung
Bestimmt die Entwicklung von Kollektivitaet und Kerndeformation
Bildet die mikroskopische Grundlage fuer Deformations- Phasen-Uebergangsverhalten (Federman-Pittel Mechanismus)
Bewirkt Besetzungszahlabhaengigkeit von Einteilchen-Energien, Energieluecken und Schalenstruktur
Professor Dr. Norbert Pietralla TU Darmstadt

45. MSSs* at the analytical Limits
Np = N =1 0+ 4+ 2+ 1+ 3+
U(5)
Vibrator
Fmax-1
MS multi-Phonon
structure
SU(3)
Rotor 3+ 2+ 1+ 2+
K=1 0+ 4+
Scissors Mode 2+
A. Richter et al.
TU Darmstadt, 1983
N.Pietralla et al.
Univ.zu Koeln, 1999 0+
* MSSs = proton-neutron Mixed-Symmetry States
Professor Dr. Norbert Pietralla TU Darmstadt

46. Professor Dr. Norbert Pietralla TU Darmstadt
Proton-Neutron symmetrische und gemischt-symmetrische Valenzraumanregungen (schematisch/geometrisch)
Deformierter Kern
Rotation
Sphaerischer Kern
Vibration
Protonen-Neutronen
ausser Phase
Scherenmode
Protonen-Neutronen
ausser Phase
Gem.-sym.
Vibration
Professor Dr. Norbert Pietralla TU Darmstadt
Animation: Robert Casperson (Yale)