Diapositive 1

1
Giant resonances, exotic modes astrophysics
1) The dipole strength r-process
Ultra-High Energy
Cosmic Rays 2) Exotic modes SuperGiant
Resonances Giant
Pairing Vibrations 3) Surprise ?
E. Khan
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1) The dipole strength
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The role of dipole strength in nuclei(de)-excitat
ion

• r-process (n,g) rates in the non-equilibrium
  canonical model
• Nuclei photodisintegration
• Statistical model of compound nuclear reaction
  Hauser-Feshbach

Tn
SnEn
(Z,A) n
Tg TE1(E) r(E) dE
Sn
0
(Z,A1)
Photon transmission coefficient sensitive
to
Tg

• the E1 strength distribution TE1(E)
• the level density r(E)

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Why using microscopic calculations ?

• Microscopic
• Efforts consuming ?
• More suited to extrapolate
• far from stability neutron skin
• Characterize the n-n interaction on the whole
  nuclear chart
• Test the model validity on a large scale

• Phenomenologic
• Fast and simple to use
• Extrapolations ?
• No feedback about nuclear structure

E1
E1
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Impact on astrophysical predictions

GDRPR
GDR
Maxwellian averaged (n,g) rates
r-abundance distributions
Effect of the Pygmy Resonance
S. Goriely, PLB436 (1998) 10
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Experiment 1

• Systematics E1 strength measurements for neutron
  rich unstable nuclei
• below Sn
• Relativistic Coulomb excitation

AGATA
70Ni
High Z
70-100 MeV/u
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Meanwhile microscopic prediction of the E1
strength

• Collective excitation in superfluid system
• QRPA in linear response small amplitude limit
  of the perturbed TD-HFB equations
  harmonic oscillations
• Connected to the Density Functional Theory
  er,k
• Since Year 2000
• Skyrme functionnal
• ?lt?(r)?(r)gt particle density
• ?lt?(r)?(r)gt pairing density

E (MeV)
r (fm-3)
E. Khan, N. Sandulescu, Nguyen Van Giai, M.
Grasso PRC66 (2002) 024309
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Comparison with experiment
GDR centroids (cf experiment 1)
SLy4
rms on GDR centroids SIII 2267 keV SGII 573
keV SLy4 457 keV MSk7 564 keV
BSk7 rms on 2135 masses 676 keV rms on
48 GDR centroids 485 keV interactions
developed with both ground and excited states
features on a large scale
(48 spherical nuclei)
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Experiment 2

• Inputs E1, level densities, masses, optical
  model potential
• Validity high level density
  Sn not too small
• Direct captures are not negligible for
  neutron-rich nuclei

Low energy section of EURISOL masses, b decay,
...
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(n,g) rates
QRPA/Hybrid
Discrepancy pheno/micro
QRPA/QRPA
Agreement HFBCS QRPA / HFB QRPA
T1.5 109 K
Deviation up to a factor 10
S. Goriely, E. Khan, M. Samyn, NPA739 (2004) 331
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Are Ultra-High Energy Cosmic Rays made of
nuclei ?
The Pierre Auger collaboration
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Ultra High energy Cosmic Rays
E1018-21 eV
GZK
Ankle
E-3
Redressed spectrum (x E3)
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Composition, acceleration propagation

• Open question !
• Extra-galactic particles protons
• nuclei (56Fe, ) ?

COMPOSITION

• Open question !
• Gamma Ray Bursts, Active Galaxy Nucleus ?
• N(E)E-b

ACCELERATION

• Quantitative answers
• Interaction with the 2.7 K Cosmic microwave
  background
• Extra-galactic Magnetic fields

PROPAGATION
Comparison with the measured spectrum on Earth
(AUGER, )
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Propagation of UHECR
2.7 K Cosmic Microwave Background
Photodisintegration cross section
g2.1010
GDR
56Fe 1021 eV

Photons density
Lorentz boosted
10
100
0.1
1
10
100
1000

E (MeV)
E (MeV)
Photodisintegration rate (1h-1)
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Photodisintegration (I)

• Pheno. and microscopic models to predict the GDR
  strength
• Photodisintegration calculated within
  Hauser-Feshbach formalism

55Mn (g,1nx)
51V (g,1nx)
Full network with beta decay rate ( r-process)
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Photodisintegration (II)
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Experiment 3

• E1 strength for Alt56 nuclei close to the valley
  of stability
• Very High intensity 109 pps for 37,39Ar

UHECR campain ? Usefull for many other
applications
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Impact on astroparticle propagation
Source 56Fe
E. Khan, S. Goriely, D. Allard, E. Parizot, et
al, Astr. Phys. 23 (2005) 191
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Interpretation of the ankle
Protons only b2.6
Protons Nuclei b2.3
Needs for a galactic CR Ankle is the
galactic/extra-galactic transition
D. Allard, E. Parizot, A.V. Olinto, E. Khan, S.
Goriely, AA 443 (2005) 29
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2) Exotic modes
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SuperGiant Resonances in neutron stars
Nuclear matter not only a toy for theoreticians
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The inner crust
r0
0.5 r0
Wigner-Seitz cells
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Supergiant resonances
L1
Excitations of drip-line nuclei immersed in
neutron gas
E. Khan, N. Sandulescu, Nguyen Van Giai, PRC71
(2005 042801
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Experiment 4

• Specific heat spectroscopy of drip-line nuclei
  drives
• the excitation spectrum of the Wigner-Seitz cells
• (low-lying states)
• Coulex or integrated (p,p)
• on the most neutron-rich Sn available (138Sn)

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Giant pairing vibrations
22O2n

• 2n transfer
• GPV high energy mode
• never observed

Khan PRC69(2004)014314
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Experiment 5

• Exotic nuclei Q value matched for high energy
  states
• Search for the GPV
• 208Pb(12Be,10Be) at 10 MeV/u

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3) Surprise
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GMR in unstable nuclei
MAYA active target
56Ni(d,d) at 50 MeV/u (GANIL)
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56Ni excitation energy spectrum
Charlotte Monrozeau PhD thesis
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Outlook

• Dipole modes plays a crucial role in nuclei
  de-excitation
• Microscopic treatment necessary to draw
  conclusions on
• r-process abundances
• Nature of UHECR
• Needs for
• Masses, b decay
• Systematic E1 data
• Low lying states close to the drip-line
• 2 neutron transfer reactions with exotic nuclei

Collective excitations in stable nuclei
exotic nuclei drip-line nuclei Fermi gas

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Microscopic models improvements
Neutron average pairing field

• Finite temperature effects
• HFBQRPA
• Future - microscopic treatment of the width
• - better treatment for odd nuclei
• - microscopic treatment of the deformation
• - phonon coupling calculations
• - drip-line nuclei coupling between
  continuum and pairing effects
• exact continuum calculations

124Sn
Dn (MeV)
Pairing phase transition
T (MeV)
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Comparison with the data

• Monte-Carlo using a extragalactic source with
  energy distribution E-b
• CMB Protons p photoproduction and e-e-
  pairs production
• Nuclei photodisintegration and
  e-e- production
• Infra Red background

Non-negligible effect with the forthcoming AUGER
data
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Next

• Magnetic field effect on the propagation of UHECR
• Nuclei in the acceleration process
• Comparison with the AUGER data

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Low and high density WS cells

• Size of the WS cells
• 1800Sn 28 fm
• 982Ge 14 fm

• Skyrme-HFB calculations with density dependent
  pairing interaction
• Non-zero value of r at the border of the WS cell

N. Sandulescu PRC 69 (2004) 045802
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Specific heat of collective modes
1800Sn
Entropy ScollSQRPA-SHFB
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Température dans les noyaux
Transition de phase superfluide
Noyaux exotiques chauds pairingcontinuumtempér
ature
E. Khan, Nguyen Van Giai, M. Grasso
NPA731(2004)311
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Accelerators of the Universe
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The QRPA residual interaction
Skyrme force and surface pairing interaction
h
SLy4 force
EQP lt 60 MeV