Nuclear excitation with zeptosecond

multi-MeV laser pulses

Adriana Pálffy and Hans A. Weidenmüller

Max Planck Institute for Nuclear Physics, Heidelberg, Germany

       Nuclear Fusion: From NIF to the Stars

San Francisco, August 11th, 2014

New experimental developments ...

ELI beam(intense & optical)

thin Carbon foil

Compton backscattering

of another laser

G. Mourou and T. Tajima, Science 331 (2011) 41

electron sheet

Experimental promise of coherent MeV photons! Challenge: the theory of laser-induced nuclear reactions

Far from yrast

yrast line

Ene

rgy

heavy ion collisions

Angular momentum

yrast

photoexcitation

0

0.05

0.1

0.15

0.2

0.25

0 10 20 30 40 50 60

Prob

abil

ity

J

# absorbed photons 30

100200

Dipole absorption

hundreds of MeV above yrast!

Nuclear excitation mechanism

N > 103

E ~ 10 MeV

T ~ 10-19 s

Giant Dipole Resonance once or twice

STRONGLY NON-ADIABATIC

H. A. Weidenmüller, Phys. Rev. Lett. 106 (2011) 122502B. Dietz and H. A. Weidenmüller, Phys. Lett. B 693 (2010) 316

PERTURBATIVE

Nucleus evaporates by multiple nucleon emission

ELI photons

QUASIADIABATIC

Compound nucleus equilibrates about as fast as it is excited

Nuclear excitation mechanism

N > 103

E ~ 10 MeV

T ~ 10-19 s

Giant Dipole Resonance once or twice

STRONGLY NON-ADIABATIC

H. A. Weidenmüller, Phys. Rev. Lett. 106 (2011) 122502B. Dietz and H. A. Weidenmüller, Phys. Lett. B 693 (2010) 316

PERTURBATIVE

Nucleus evaporates by multiple nucleon emission

ELI photons

QUASIADIABATIC

Compound nucleus equilibrates about as fast as it is excited

Competing channels

PHOTOEXCITATION RESIDUAL INTERACTION

creates particle-hole pairs nucleon-nucleon interactionredistributes energy

Competing channels

PHOTOEXCITATION RESIDUAL INTERACTION

creates particle-hole pairs nucleon-nucleon interactionredistributes energy

Quasiadiabatic regime – after each absorption, nucleus equilibrates!!!

Competing channels

PHOTOEXCITATION INDUCED PHOTOEMISSION

creates particle-hole pairs particle-hole recombination andphoton emission

PHOTOEXCITATION NEUTRON EVAPORATION

Bye bye and thanksfor all the fish!!!

creates particle-hole pairs

Competing channels

after several absorbed photons

PARTICLE EMISSION NEUTRON EVAPORATION

Bye bye and thanksfor all the fish!!!

single nucleons reach the continuum

Competing channels

after several absorbed photons

NEUTRON EVAPORATION

Bye bye and thanksfor all the fish!!!

Competing channels

after several absorbed photons

Bye bye and thanksfor all the fish!!!

PARTICLE EMISSION

single nucleons reach the continuum

NEUTRON EVAPORATION

after several absorbed photons

Bye bye and thanksfor all the fish!!!

a neutron

PARTICLE EMISSION

single nucleons reach the continuum

Bye bye and thanksfor all the fish!!!

Competing channels

NEUTRON EVAPORATION

after several absorbed photons

Bye bye and thanksfor all the fish!!!

a neutron or a proton

PARTICLE EMISSION

single nucleons reach the continuum

Bye bye and thanksfor all the fish!!!

Competing channels

Quasiadiabatic regime

Assume complete nuclear equilibration between two photon absorptions

Effective absorption rate of an equilibrated compound nucleus

COMPETING WITH

Induced dipole emission

Induced nucleon emission

Neutron evaporation

Fission

Level densities needed! New theoretical formalism for high energies and high particle-hole numbers!

Shell model with finite number of bound states A spinless non-interacting fermions distributed

STEP I: CONSTANT SPACING MODEL

“Corrected” Gaussian, 2nd, 4th, and 6th moments

AP and H. A. Weidenmüller, Phys. Lett. B 718, 1105 (2013)

51 states

d

Level densities

More realistic case, level spacing linear or quadratic in energy

Shift in energy Slight asymmetryNarrower width

AP and H. A. WeidenmüllerNucl. Phys. A 917, 15 (2013)

STEP II: REALISTIC SPACING

10-35

10-30

10-25

10-20

10-15

10-10

10-5

100

1500 2000 2500 3000 3500 4000

RA

(E)

E(MeV)

ct. sp.lin. sp.

Density of accessible states - Fermi gas model

148 states A=100

!!! At maximum of level density, photon absorption and emission are equally probable!!!

Comparison

AP and H. A. WeidenmüllerPhys. Rev. Lett. 112, 192502 (2014)

!!! At maximum of level density, photon absorption and emission are equally probable!!!

Comparison

AP and H. A. WeidenmüllerPhys. Rev. Lett. 112, 192502 (2014)

Comparison

Emission of slow neutrons feeds states of similar energy in the daughter nuclei

For a 50 zs pulse, proton-rich reaction products – FAR FROM STABILITY

Nucleon emission – p or n - details depend on exact binding energiesand absorption rates

AP and H. A. WeidenmüllerPhys. Rev. Lett. 112, 192502 (2014)

Conclusions

End of reaction chain determined by duration of laser pulse – 50 zs

nuclear excitation with a multi-MeV zs coherent laser pulse

0

0.05

0.1

0.15

0.2

0.25

0 10 20 30 40 50 60

Pro

babi

lity

J

# absorbed photons 30

100200

leads far from yrast and far from stability!!!

nuclear reaction theory + newly developed method for nuclear level densities

AP and H. A. WeidenmüllerPhys. Lett. B 718, 1105 (2013)Nucl. Phys. A 917, 15 (2013)

proton-rich nuclei due to strong neutron evaporation

Quasi-adiabatic regime 1 photon absorbed / nuclear relaxation time

AP and H. A. WeidenmüllerPhys. Rev. Lett. 112, 192502 (2014)