Comprehensive investigation of nuclide production cross sections in 238U(1AGeV)+d J.Pereira1, P.Armbruster2, J.Benlliure1, M.Bernas3 ,A.Boudard4, E.Casarejos1, S.Czajkowski5, T.Enqvist2, R.Legrain4, S.Leray4, B.Mustapha3, M.Pravikoff5, F.Rejmund3, M.V.Ricciardi2, K.-H.Schmidt2, C.Stéphan3, J.Taieb3, L.Tassan-Got3,C.Volant4, W.Wlazlo4 1USC, E-15706 Santiago de Compostela, Spain 2GSI, Planckstrabe 1, D-64291 Darmstadt, Germany 3IPN Orsay, IN2P3, F-91406 Orsay, France 4DAPNIA/SPhN CEA/Saclay, F-91191 Gif sur Yvette, France 5CENBG, IN2P3, F-33175 Gradignan, France

Residue production of 238U(1A GeV)+d measured with the FRS at GSI Around 1500 residues have been measured and identified Production cross sections have been measured with precission of 5-15% Kinematical properties were determined for each nucleus Fission and fragmentation residues were separated

Underlying physics in the 238U+d system Fissility Excitation energy Shell effects M.Bernas et al. J. Taieb T. Enqvist et al.

Spallation reactions:Two-step model First stage: production of a thermalized prefragment Interaction of projectile and target: Intranuclear cascade (Isabel, INCL) Emission of preequilibrium particles Excitation energy, mass and angular momentum of prefragment Second stage: deexcitation of prefragment Two decay modes: evaporation of particles and fission (Abla) Evaporation of particles: statistical model (Ewing-Weisskopf) Fission: Transition-state model (Bohr-Wheeler)

More details: talk of B.Jurado in this conference The fission reaction mechanism at high excitation energies: 208Pb(1AGeV)+p Statistical description of fission: Transition-state model (Bohr-Wheeler) Dynamical description of fission: Coupling between collective (deformation) and intrinsic degrees of freedom: dissipation coefficient b T.Enqvist et al. Fission is well described with both cascades and with a dissipation coefficient b=2x10-21 s-1 More details: talk of B.Jurado in this conference

The onset of a break-up stage at high excitation energies The reaction mechanisms at higher excitation energies: 208Pb (1 A GeV)+d At high excitation energies: Light fragmentation residues underestimated Fission residues overestimated The onset of a break-up stage at high excitation energies High excitation energy: Deexcitation by simultaneous decay into several fragments (Break-up) Low Excitation energy: Deexcitation of compound nucleus by statistical decay (Fission and Evaporation) Onset of break-up stage: TBU = 5 MeV T.Enqvist et al. K.-H. Schmidt et al., Nucl. Phys. A710 (2002) Data well reproduced with ISABEL + dissipation + break-up decay Fission overestimated with INCL

Differencies between ISABEL and INCL Fission cross sections overestimated with INCL Large angular momenta J reduces fission barriers INCL overestimates angular momentum

Isobaric distributions in 238U(1AGeV)+p, d M.Bernas et al. M.V.Ricciardi J.Taieb et al. E.Casarejos J.Pereira

Shell effects and collective excitations on the system 238U+d Shell effects are compensated with collective excitations

Summary The reaction 238U(1AGeV)+d is a complicated system (high fissility, high excitation energies, shell effects,...) The precision and completeness of the data demand highly accurate implementation of the physical ingredients of the models Fission is well described with a dynamical model (dissipation) Break-up stage must be included at high excitation energies (T>5MeV) INCL seems to overestimate the angular momentum of the prefragment Shell effects and collective excitation must be included in the description of the level densities