norbert pietralla tu darmstadt1 1. feb. 2010 current themes of nuclear research and how the eli...

Norbert Pietralla TU Darmstadt 11. Feb. 2010

Current Themes of Nuclear Research

and how the ELI photonuclear pillar could contribute to them

Norbert Pietralla

DirectorInstitut für Kernphysik

Darmstadt University of Technology

(TUD)

Collaborative Research CenterSFB634

Research Center of ExcellenceNuclear and Radiation Physics

TUD

Exploring nuclei with lasers


Vision of Nuclear PhysicsUnderstanding the properties of heavy atomic nuclei quantitatively and predictably from their basic constituents, quarks and gluons, and from the interactions between them.


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,…


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…

Relevant nuclear themes

e.g. Nuclear Structure and Astrophysics

Relevance for

Astrophysics


Central Topics for Nuclear Structure

Halos

Neutron Skins Neutron stars

Pygmy Resonance

EOS

• 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)


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


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“


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

Energy / MeV

5 15(γ,γ‘) (γ,n)

Giant Dipole ResonancePygmy-

Dipol Resonance

Two-Phonon-

State

Sn

x


Photonuclear Reactions

gs

´

Separationthreshold

AX

A´Y Nuclear Resonance Fluorescence (NRF)PhotoactivationPhotodisintegration

Absorption

(-activation)

´


HIgS Beam Profile

N.Pietralla et al. Phys. Rev. Lett. 88012502 (2002).


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


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

E < 10 MeV

Cu


Spectroscopy near separation threshold


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).

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 ?

skincore


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

eV-resolving spectroscopy with photon beams


Principle of Self-Absorption

absorber nuclei:

photons of decay processes:

E0

Ef

Ej

Jf

Jj

J0

Γj0

Γfj

Γ0Γ0Γ0

e

Absorber


Photon flux density after 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

scatterer

bremsstrahlungradiator

calibrator

electrons

absorber

absorber spectrum

detector

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

Principle of Self-Absorption


Measuring principle II


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)


Determine ground state transition width Γ0

• self-absorption R can be calculated analytically• it depends on K and thus on

• reminder:

• determine self-absorption experimentally and compare with calculation


Test of „the branching Assumption“ Γ0/Γ ≈ 1Access to -ray strength function

• green line: branching ratio into ground state is = 1

• branching ratio can‘t 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?!


Potential for ELI photonuclear pillar‘shigh-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…


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 !


Thank you !


Azimuthal asymmetry → parity quantum no.

Parity Measurements with Linearly Polarized Photon Beams


40Ar

First observation of a 1+ state of 40Ar


Astrophysical Relevance of M1 Data

Darmstadt data 54Fe

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


Polarization in the entrance channel

• Linear polarization (HIS)spin/parity program (since 2001)

• Circular polarization (HIS, S-DALINAC)parity non-conservation

20Ne, 238U

targetcircular

-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 !


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”


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

norbert pietralla tu darmstadt1 1. feb. 2010 current themes of nuclear research and how the eli...

Documents

nuclear matter

outline nuclear physics

vision of nuclear physics

shell model slide

lasers slide

photonuclear physics

relevant nuclear themes

market summary slide