_Physics experiments with high energy lasers高能量激光核物理实验课件.ppt

ICUIL 2010 Atomic levels are sensitive to the nucleus charge distribution and nuclear properties depend on the atomic environment Effect of ionisation on nuclear lifetimes - 7Beneutral t1/2 =52 d (EC decay) while 7Be4+ : stable - first excited level of 125Te (Z=52, E=35.5 keV) Q=0 T1/2=1.5 ns (internal conversion + M1) Q= 47+ T1/2 = 6 ± 1 ns F.Attalah et al., Phys.Rev.Lett. 75(1995) 1715 Nuclear excitation processes in plasma ? NEET Resonnant process caracterized by: Energy mismatch : d Quantum selection rules Experimental setup Numbers….. conclusion NEET Constraints: Possible only for very few stable nuclei initially in their ground state: 57Fe, 181Ta, 201Hg, 235U Excited level 14.4 keV 6.2 keV 1.56 keV 76.8 eV Energy Lifetime 98.3 ns 6 μs 81 ns 27 min Thermodynamic Equilibrium Nucleus populations (Boltzmann law) in state i with an excitation energy Ei and spin Ji Thermodynamic Equilibrium Equilibration time (under stationary conditions) Populations at equilibrium Multi-field Modeling Microscopic model : quantum tools Fermi Golden rule Time dependant perturbations Partial wave scattering (PWBA, DWBA, …) Macroscopic model Relativistic average atom Statistical Thermodynamics Plasma Physics Lasers are tools to produce big volumes of plasma and to accelrate particules. What is exciting about this? plasma not only the nuclear properties are modified but also new nuclear excitations modigations are possible They are also modified, * Plasma is not only a medium made of ionized atoms but these atoms are inside a photon bath. Depending on the temperature of this bath, nuclear excitation may be possible and induce also modifications of nuclear properties such as lifetimes. The extreme conditions created in a plasma permit to study the influence of the environment on the nuclear states half-life . Calculations performed by Klay et al in 1991 shown that the effective half-life of the 176