Nuclear Physics with ELI, Population/depopulation of Isomers: modification of nuclear level lifetime

1
Nuclear Physics with ELI, Population/depopulation
of Isomers modification of nuclear level
lifetime
F. Gobet, C. Plaisir, F. Hannachi, M. Tarisien,
M.M. Aléonard CENBG, Université de Bordeaux,
CNRS,IN2P3 V. Méot, G. Gosselin, P. Morel ,
CEA/SPN, Bruyères le Châtel P. Audebert et al.,
LULI Polytechnique
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Nuclear Physics with ELI

• Great interest in a PW laser with a high
  repetition rate for Nuclear Physics
• Typically gt1 Hz ( mbarn or sub-mbarn cross
  sections )
• A facility to produce - high energy electrons,
  protons
• - (dense and warm) plasma
• - intense (E,B) field
• Allowing several synchronous laser beams with
  modular temporal characteristics 10 fs to ns(?)

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With a high power laser it is possible to
1) create a (warm and dense) plasma
2) create a bunch of high energy particles
3) Excite nuclei (inside the plasma)
E 1010 V/cm B 1000 T
4) Submit these nuclei to high electromagnetic
fields or second production particles
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Can nuclear lifetime be modified in a plasma?
What we know the effect of the ionization on the
electronic shells
Internal Conversion can be modified, eventually
suppressed T1/2
neutral
125mTe (first excited state at 35,49 keV) 52
(1)
48
Other deexcitation modes of the nucleus may
appear T1/2 Resonant Internal Conversion on
unoccupied bound states has been shown.
Resonant Internal Conversion on occupied bound
states is predicted in 187 Au (2) (experiment at
GANIL)

1. T. Carreyre et al, Phys. Rev.C 62 (2000), 024311
2. F.F. Karpeshin et al. PRC 65, 034303 (2002)

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Can nuclear lifetime be modified in a plasma?
In a plasma excitation of intermediate states,
can modify the effective lifetime of a nuclear
state
72
71
ß-
(n,?)ß-
70
10 keV
N.Klay et al. PRC 44,2839 (1991)
176Lu abundance cosmochronometry,
cosmothermometry, and s-process branching
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Enhanced deexcitation of isomers the 84Rb
isomer, a laboratory case similar to 176Lu
2) laser (warm plasma) for isomer excitation
9 ns
D 3.4 keV
M1
1) Petawatt laser to populate the isomer
85Rb(g,n)84mRb
0.463 MeV
20
3) Observation of a 251 keV g
0.248 MeV
Eg248 keV
32.7 d
CENBG,LULI, CEA-DAM-DPTA, collaboration
84Rb
85Rb(g,n)84mRb cross section just measured at
the ELSA (19 MeV) electron facility (Bruyères le
Châtel) analysis under process
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Pumping the isomer state
Several processes are competing to the
excitation of a nucleus in a plasma via photon
absorption, inelastic scattering of electrons or
via the electronic shell structure (NEET,
NEECprocesses)
Excitation rate of the 6- level in 84Rb as a
function of the plasma charge state
Hypothesis T plasma 2keV charge states
gt28 during ?t10 ps 1ns Several 100 excited
isomers (detection possible)
?Experimental data for the theoretical models of
nuclear excitations in plasma
? plasma 0,01g/cm3 (Gosselin et al PRC 70
(2004) 064603 and PRC 76 (2007) 044611
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Multilevel system indirect deexcitation process
or lifetime modification

• The 93Mom case

0.2 keV
93Nb(p,n)93Mom
Lifetime 5 orders of magnitude decrease
G.Gosselin, V.Meot and P.Morel PRC 76 (2007)
044611
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84Rb
Excitation energy
219.1 keV g
248 keV g
Partial level scheme of 84Rb
2 gammas to be detected
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85Rb(g,n)84mRb
Petawatt electron production laser (50 fs, 10J,
?20µm)
converter
85 Rb
?
Laser 1
Electrons
Shielded ? ray detector
?
Al target
Laser 2
Absolute need high repetition rate for the 2
laser beams
Long pulse large diameter (20 ns, ?700 µm) to
create plasma conditions after the Petawatt shot
(up to a some minutes after Petawatt shot) Or
other excitations e,e, photoexcitation, with
another Petawatt laser
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Requests on laser characteristics

• High brightness for secondary particle sources
• short pulse
  (10-100 fs) I gt 1020 W/cm2
• High repetition rate to overcome low cross
  sections 1 Hz lt rate lt 1 kHz
• Large warm plasma long pulse (ns?) I1014
  W/cm2,
• focal spot 500 µm2
• High electromagnetic fields
• Great interest of lasers they afford several
  synchronous beams to
• - excite nuclei or produce new species
• - explore their properties in a plasma, in a
  high (E,B) field,
• or via another excitation with secondary
  particles
• possibility of different kind of particles on
  the same target !!
• To meet these requests we need several laser
  beams with different energy and pulse length

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Collaborators CENBG, CNRS/IN2P3, Univ. Bordeaux
1 CEA/DPTA/SPT/Bruyères le Châtel LULI,
Polytechnique, Palaiseau Members of the Institut
Laser Plasma (France) Open to other
collaborators
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• Phys. Rev. C 73, 045806 (2006) 7 pages
• Solar abundance of 176Lu and s-process
  nucleosynthesis
• J. R. de Laeter and N. Bukilic
• An accurate determination of the abundance of
  176Lu is required because of the importance of
  this isotope in cosmochronometry,
  cosmothermometry, and s-process branching
  studies. An accurate abundance of 176Lu is also
  required as it is the parent nuclide of the
  176Lu/176Hf geochronometer.