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Nuclear Physics with ELI Populationdepopulation of Isomers Cross Rate
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 Nuclear Physics with ELI Great interest in a PW laser with a high repetition rate for Nuclear Physics: Typically >1 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(?) With a high power laser it is possible to : 1) create a (warm and dense) plasma 2) create a bunch of high energy particles protons, electrons, photons 3) Excite nuclei (inside the plasma) E 1010 V/cm 4) Submit these nuclei to high electromagnetic B 1000 T fields or second production particles 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 e- 125mTe t 1 1.49ns (first excited state at 35,49 keV) 2 52 (1) 48+ t 1 11 ns 2 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) 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 β- 70 (n,)β- 10 keV N.Klay et al. PRC 44,2839 (1991) 176Lu abundance cosmochronometry, cosmothermometry, and s-process branching Enhanced deexcitation of isomers : the 84Rb isomer, a laboratory case similar to 176Lu 2) laser (warm plasma) for isomer excitation 9 ns M1 D = 3.4 keV 1) Petawatt laser 85Rb(,n)84mRb 0.463 MeV 20’ to populate the isomer 3) Observation 0.248 MeV E=248 keV of a 251 keV 32.7 d CENBG,LULI, CEA-DAM-DPTA, collaboration 84Rb 85Rb(,n)84mRb:cross section just measured at the ELSA (19 MeV) electron facility (Bruyères le Châtel); analysis under process 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, NEEC…processes) Excitation rate of the 6- level in 84Rb as a function of the plasma charge state Hypothesis: T° plasma ~ 2keV: charge states >28 during Dt:10 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 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 84Rb Excitation energy 219.1 keV 248 keV Partial level scheme of 84Rb 2 gammas to be detected 85Rb(,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 Requests on laser characteristics High brightness for secondary particle sources: short pulse (10-100 fs) I > 1020 W/cm2 High repetition rate to overcome low cross sections: 1 Hz < rate < 1 kHz Large warm plasma long pulse (ns?): I~1014 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 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 • 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.
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