Current Themes of Nuclear Research and how the ELI photonuclear pillar could contribute to them

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Current Themes of Nuclear Researchand how the
ELI photonuclear pillar could contribute to them
Exploring nuclei with lasers
Norbert Pietralla Director Institut für
Kernphysik Darmstadt University of
Technology (TUD)
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Vision of Nuclear Physics
Understanding the properties of heavy atomic
nuclei quantitatively and predictably from their
basic constituents, quarks and gluons, and from
the interactions between them.
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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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But still

• Present theory still needs phenomenology for
  quantitative reliability
• Phenomenology requires input from data
• The less is known, the worse does theory
• Quest for extreme conditions

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Relevant nuclear themese.g. Nuclear Structure
and Astrophysics
Relevance for Astrophysics
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Central Topics for Nuclear Structure

• Quest for the limits of existence
• Halos, Open Quantum Systems, Few Body
  Correlations
• Changing shell structure far away from stability
  
• Skins, new collective modes, nuclear matter,
  neutron stars
• Phases and symmetries of the nuclear many body
  system
• Origin of the elements
• ? unified theory (ab-initio, density functional,
  shell model)

EOS
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Outline

• Nuclear physics with low-energy photons
  (nuclear dipole physics)
• ELI day 1
• Exploring the weakly bound
  Measurements near separation threshold
• Exploring the unknown
  Highest resolution (eV /
  MeV)-spectroscopy
• Exploring the dangerous
  radioactive-waste
  management (multi-billion market)
• Summary

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Photonuclear Physics withMeV-range photon beams

• Pure EM-interaction
• (nuclear-) model independent
• small cross sections, penetrating, thick
  targets
• Minimum projectile mass
• min. angular momentum transfer,
  spin-selective dipole-modes
• Polarisation
• Parity physics

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Realm of photonuclear structure physics

• Electric Dipole strength concentrated in GDR
  above and in PDR below particle separation
  threshold
• Photonuclear reaction useful tool for
  investigation of dipole strength

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Photonuclear Reactions
Absorption
gs
AX
Nuclear Resonance Fluorescence (NRF) Photoactivati
on Photodisintegration
(-activation)
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HIgS Beam Profile
N.Pietralla et al. Phys. Rev. Lett. 88 012502
(2002).
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Traditionally Bremsstrahlung Kneissl,Pietralla,Zi
lges, J.Phys.G 32, R217 (2006).
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S-DALINAC facility at IKP TU Darmstadt
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Darmstadt Low-Energy Photon Scattering Site at
S-DALINAC
Ge(HP) g-detectors
Cu
Cu
lt 10 MeV
Target
g
e-
Radiator target
Electrons
Bremsstrahlung
E? lt 10 MeV
Intensity
Intensity
Energie
Energie
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Spectroscopy near separation threshold
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Systematics of the Pygmy Dipole Resonance

• Concentration
• around 5-7 MeV
• Strong fragmentation
• Summed strength Scaling with N/Z ?
• Mass dependence of
• ?-ray strength function ?

A. Zilges et al., PLB 542 (2002) 43. S. Volz et
al., NPA 779 (2006) 1. U. Kneissl, NP et al.,
J.Phys.G 32, R217 (2006).
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eV-resolving spectroscopy with photon beams

• aim determination of transition strengths need
  absolute values for ground state transition width
• NRF-experiments give product with branching
  ratio
• assumption
• no transition in low-lying states observed
• but many small branchings in other states?
• self-absorption measurement of absolute ground
  state transition widths

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Principle of Self-Absorption
e
Absorber
absorber nuclei
photons of decay processes
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Interaction within the absorber

• atomic attenuation
• mainly Compton effect
• Klein-Nishina formula

• resonance absorption
• depends on G0
• Doppler cross section

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Photon flux density after absorption
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Principle of Self-Absorption

• problem resolution of modern detectors by far
  too low
• solution scattering target made of same material
  as absorber is highly resolving detector (same
  resonances ? sensitive on change in photon flux)
• two measurements one w/ and one w/o absorber

• self-absorption decrease of decays in scatterer
  because of resonant absorption

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Measuring principle II
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Recent results (140Ce)

• scatterer 2 g 140Ce
• calibrator 312 mg 11B
• absorber 60 g CeO2
• endpoint energy 8 MeV
• measuring time in each case about 4 days
• Photon flux 103 ?/(s eV cm2)

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Determine ground state transition width G0
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Test of the branching Assumption G0/G
1Access to ?-ray strength function

• green line branching ratio into ground state is
  1
• branching ratio cant be larger than 1 points
  have to lie above green line
• two transitions with small branching into ground
  state (large errros)
• many points agree with green line
• one point clearly underneath green line not one
  strong but two weaker transitions of close lying
  states?!

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Potential for ELI photonuclear pillarshigh-flux
high-resolution ?-ray beam

• Improvement by 3 orders of magnitude in photon
  flux is feasible
• Will open up new horizons for photonuclear
  research
• Nuclear dipole strength near threshold
• Fine structure of quadrupole response
• Energy resolution on Doppler-width scale
• Detection of hazardous material in bulk matter
• New approaches

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Summary

• Nuclear structure physics with ?-ray beams is a
  vivid field with high discovery potential
• ELI can become a major facility in this field
• Needs - energy-tunable, high-flux,
  high-rep.rate, high-resolution, polarized ?-ray
  beam from LASER-Compton backscattering
• All this should be possible at ELI !

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Thank you !
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Parity Measurements
Principle of a Compton-Polarimeter
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Modest polarisation sensitivity Better use
polarized ?-ray beams !
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Parity Measurements with Linearly Polarized
Photon Beams
Azimuthal asymmetry ? parity quantum no.
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Testing shell structure from M1 Spin-flip
excitation
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First observation of a 1 state of 40Ar
40Ar
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• Duke-Stony Brook expt.
• high-pressure Ar gas
• HIgS polarized g-beam
• 7.7 MeV lt E lt 11 MeV
• analyzing power 50

Duke Stony Brook data (2 examples)
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T.C.Li, NP et al, Phys.Rev.C (2006).
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Astrophysical Relevance of M1 Data
Langanke et al., PRL (2004). Neutrino-cross
sections
Darmstadt data 54Fe
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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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Polarized Beams
250 keV Thermionic Electron Gun
100 keV Polarized Electron Gun
10 MeV Injector
To Experimental Hall
5 m
Spatial restriction transport of accelerator
equipment
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S-DALINAC Polarized INjector (SPIN)

• Design of polarized injector beam line finished
• (Prof.Dr.J.Enders)
• Installation begins middle of January 2010

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• 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
Forward-backward asymmetry ? Parity-violation Weak
interaction
circular
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• 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

target
circular
Forward-backward asymmetry ? Parity-violation Weak
interaction
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The 20Ne case parity mixing of yrast levels
Goal measure parity violation in simple states
! Understand effects of weak interaction microsco
pically ? e.g., study the parity doublet in 20Ne
!
Tlt0
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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)
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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
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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

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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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Once the atomic nucleus is formed effective
(in-medium) forces can generate simple pattern.
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Role of Isovector Spin-flip M1 excitations in
Nuclear Physics
E (MeV)
Quark-Spin-flip
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Overview dipole modes
Spin M1 Strength
Exotic Modes
Orbital M1 Strength Scissors mode,
B(M1)
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Electric Giant Dipol Resonance (GDR)
E1
Sensitive to average Proton-Neutron-Restoring
Force but insensitive to shell structure need
low-energy E1/M1 data !
Data from A.Bohr, B.Mottelson Nuclear
Structure
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Scissors Mode in Deformed Nuclei (Darmstadt, 1983)
Scissors mode classically current loop gt
M1 magnetic dipole excitation electron
scattering photon scattering
Bohle et al., NPA 458, 205 (1986).
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M1 phenomena in the nuclear valence shell
Collectivity of the Scissors Mode
Richter, Kneissl, von Brentano et al.
Measure of quadrupole collectivity
Stuttgart-Darmstadt-Köln
2
1
N. Pietralla et al., PRC 58, 184 (1998)
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MSSs at the analytical Limits
Np N? 1
SU(3) Rotor
3
2
1
2
K1
0
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Scissors Mode
2
A. Richter et al. TU Darmstadt, 1983
N.Pietralla et al. Univ.zu Koeln, 1999
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MSSs proton-neutron Mixed-Symmetry States
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Proton-Neutron symmetrische und
gemischt-symmetrische Valenzraumanregungen
(schematisch/geometrisch)
Sphaerischer Kern Vibration
Deformierter Kern Rotation
Protonen-Neutronen ausser Phase Gem.-sym. Vibratio
n
Protonen-Neutronen ausser Phase Scherenmode
Animation Robert Casperson (Yale)