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)