Evidence for Multiphonon Giant Resonances in Electromagnetic Fission ofU238

Abstract

Differential cross sections for electromagnetic fission of 238U projectiles (500 MeV/u) in C, Sn, and Pb targets are measured and analyzed in terms of single- and multiphonon giant resonance excitations as doorway states to fission. A novel experimental method exploits the linear relationship between neutron multiplicity and the primary 238U excitation energy. Multiphonon states contribute up to 20% of the cross section; a component at high excitation energies is indicated that may arise from three-phonon dipole and two-phonon GDR x GQRiv giant resonance excitations.

Relativistic Coulomb Excitation within the Time Dependent Superfluid Local Density Approximation

“…10 6 fm/c. Since our simulations times are much shorter we are not able to see emission of the second photon, as reported in experiment [7,8], where two photons were measured in coincidence. In our calculations we have followed the nuclear evolution during approximately 2500 fm/c after collision.…”

“…From the theoretical point of view, Coulomb excitation can be treated as a textbook example of a nuclear system being subjected to an external, time-dependent perturbation. However, in order to be able to probe nuclear collective modes involving multi-phonon states for example [7,8], a large amount of energy has to be transferred to the nuclear system. Thus the interaction time should be relatively short and the velocity of the projectile has to be sufficiently large for an efficient excitation of nuclear modes of frequency ω, the collision time τ coll = b/γv has to fulfill the condition that ωτ coll ≃ 1.…”