professor dr. norbert pietralla tu darmstadt nuclear structure physics at 4gls norbert pietralla...

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


Vision of Nuclear Physics

Understanding the properties of heavy atomic nuclei from their basic constituents, quarks and gluons, and from the interactions between them.


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)


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,…


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.


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


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“


Nucleon-Spin-flip

Role of Isovector Spin-flip M1 excitations in Nuclear Physics

E(MeV)

Quark-Spin-flip


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


Photonuclear Reactions

gs

´

Separationthreshold

AX

A´Y Nuclear Resonance Fluorescence (NRF)PhotoactivationPhotodesintegration

Absorption

(-activation)

´


Traditionally Bremsstrahlung: Kneissl,Pietralla,Zilges, J.Phys.G 32, R217 (2006).


Overview: dipole modes

Exotic Modes

B(M1)

Orbital M1 StrengthScissors mode,…

Spin M1 Strength


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


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


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


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 ?


Parity Measurements

Principle of a

Compton-Polarimeter


Modest polarisation sensitivity

Better use polarized -ray beams !


Azimuthal asymmetry → parity quantum no.

Parity Measurements with Linearly Polarized Photon Beams


HIgS Beam Profile


Testing shell structure from M1 Spin-flip excitation


40Ar

First ever observation of a 1+ state of 40Ar


T.C.Li, NP et al, Phys.Rev.C (2006).


Astrophysical Relevance of M1 Data

Darmstadt data 54Fe

Langanke et al., PRL (2004).Neutrino-cross sections


Direct Measurement of B(GT) from Charge-Exchange Reactions

Osaka-data

Fujita et al., PRL(2005).Adachi et al.,PRC (2006).


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


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 !


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)


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”


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 nuclear structure physics at 4gls norbert pietralla...

Documents

ikp tu darmstadt

flip slide

mev cu slide

spin m1 strength slide

comptonpolarimeter slide

radiation physics tud

deformed nuclei darmstadt

m1 spinflip excitation