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Coulomb Excitation of Multi Phonon Giant Resonances at SIS在SIS多声子巨共振库仑激发
Coulomb Excitation of Double Phonon Giant Resonances Programme Motivation Introductory Remarks Experimental Technique Results Coulomb excitation of the DGDR Hints for non-harmonic behaviour Decay properties Summary A Motivation Coulomb Excitation of Relativistic HI-Projectiles Very high excitation cross sections Efficient detection in 4p Observation of rare processes Investigation of radioactive isotopes Multi-Phonon Giant Resonances:highly collective, (large) amplitude motions New test field for microscopic theories Doorway states to “exotic” decay processes? The Virtual Photon Field Equivalent photon spectrum defined for all multipolarities(e.g. Bertulani, Baur; Phys. Rep. 163,5 (88)) Adiabatic Cut-off: Preferable energy window Coulomb Excitation in a Simplified Model Method of virtual photons (Weizs?cker/Williams)equivalent (cross sections) to semi-classical treatment Lorentz-contracted field acts for a short interval Dt. Small momentum transfer (independent of g) Strong transverse field Giant Resonances(a reminder) Small amplitude collective motion (shape/density, electric/magnetic) Linear response a.f.o. relevant co-ordinate cross feature of all isotopes Appears as a broad structure Strongly damped motion due to a coupling of the coherent 1p-1h state to incoherent 2p-2h (doorway states) states Excitation and Dissociation Compound nucleus decay dominant Direct g-decay: Gg / Gtot ? 1.7 (0.9) % (Beene et al., PR C41 (90) 920) Direct neutron decay: Gdirect / Gtot ? few % (van der Woude et al., NP A569 (94) 383c) Multiple excitation of the GDR N-phonon state of the GDR (assume harmonic oscillator) excitation probability:Poisson distribution Energy: v ? c: s(GR) 1 barns(GR ? GR) 100 mb The LAND approach Exclusive measurement of the projectile decay products using inverse kinematics ! Set-up: Neutrons: Large Area Neutron Detector Photons: Crystal ball, (BaF-array) Projectile: Scintillators, MWPC, Strip detectors, PIN
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