Winfried Wilcke

Reaction parameters for heavy-ion collisions

Abstract These tables present reaction parameters for all combinations of 27 projectile and 16 target nuclei in a laboratory bombarding energy range of 1–50 MeV/u. The reaction parameters are derived from the Fresnel model of heavy-ion scattering, the droplet model, and the rotating liquid-drop model, or from systematics of experimental data.

Hexadecapole moments obtained by semiclassical and quantum mechanical analyses of Coulomb excitation

Electric quadrupole and hexadecapole matrix elements of rare-earth nuclei were determined from Coulomb excitation of the 2+ and 4+ rotational states in the ground-state band. The E4-matrix elements obtained second-order perturbation expansion of the quantum mechanical theory and by a coupled channel code agree within 20%.

A two-dimensional position sensitive ΔE-E counter for energetic light charged particles

Abstract A large area position sensitive ΔE - E detector for energetic light charged particles is described. A single wire gas proportional counter is used as the ΔE detector, with stop detectors consisting of three 19 mm thick NE 102 scintillators coupled to RCA 8053 photomultipliers. The total active area of the ΔE - E detector is 43 cm 2 . Two dimensional position readout is obtained from the proportional counter by a combination of charge division and electron drift time measurements. The detector is suitable for α-particles with energies between 6.5 and 180 MeV. Position resolution is 1 mm in both dimensions, ΔE resolution is 10% and the energy resolution of the scintillators is 3%. The detector is compact enough to fit in a 30″ scattering chamber, where solid angles ≳200 msr may be attained. An application of this detector in studies of charged particle emission in a heavy ion induced reaction is discussed.

Study of nuclear-coulomb interference effects in inelastic deuteron scattering on 238U☆

Abstract The angular distributions of elastically and inelastically scattered deuterons from 238 U at E = 17 MeV are compared to coupled-channel calculations. The cross sections at small scattering angles are strongly influenced by nuclear-Coulomb interference effects and allow a simultaneous extraction of nuclear (optical potential) and charge quadrupole deformation parameters. Two different deformed Coulomb potentials and the parameters of the optical model are discussed.

Influence of form factors and multistep effects on the 232Th(d, t)231Th reaction

Abstract The angular distributions and cross sections of the 232 Th(d, t) 231 Th reaction at a laboratory bombarding energy of 17 MeV have been measured and are compared to the results of DWBA and CCBA calculations. The influence of different form factors calculated in spherical and deformed Saxon-Woods potentials is studied and found to be important. The choice of the deuteron optical potential is discussed.

Alpha-particle emission in the strongly damped reaction of 165Ho + 56Fe at 8.3 MeV/nucleon

Abstract Alpha-particle emission in coincidence with damped reaction fragments is studied for the 165 Ho + 56 Fe (E lab = 465 MeV) reaction. Statistical emission from the two fully accelerated strongly damped reaction fragments accounts for the dominant sources of the α particles. The α-particle multiplicity M α depends strongly on the fragment excitation energy and atomic number, with an average multiplicity 〈 M α 〉 = 0.2 for Fe-like fragments from damped reaction events with − Q > 100 MeV. Temperatures derived from neutron and α-particle spectra are in good agreement.

Distinctive features of heavy ton dissipative collisions

Abstract Examples of experimental angular, charge (mass) and energy distributions of reaction products from damped heavy-ion reactions are presented. Correlations between these observables, as well as with the associated light particles emitted in the deexcitation stage, are illustrated and shown to give important insights into the reaction mechanism of dissipative collisions. Comparisons of experimental results with dynamical transport calculations based on one-body nucleon exchange give strong evidence that stochastic exchange of independent nucleons account for the dominant part of the dissipative and fluctuative phenomena observed in damped reactions.

Neutron emission in the reaction Ho-165 + Fe-56 at Elab=8.5 MeV/u

Neutron emission and ..cap alpha..-particle emission in the /sup 165/Ho + /sup 56/Fe reaction have been measured for the damped-collision and fusion-fission components of this reaction at a bombarding energy of 8.5 MeV/u. The c.m. neutron energy spectra for damped collisions indicate equal temperatures for the light and heavy fragments, a result consistent with the equilibration of the excitation energy during the interaction time. Pre-equilibrium neutron emission is found to contribute less than 5%. An out-of-plane neutron anisotropy A/sub 2/ = 0.2 +- 0.1 is found. The measured ratios of the neutron multiplicities for the light and heavy fragments suggest a rapid approach of the fragment N/Z ratios during the collision to that corresponding to minimum potential energy of the composite system.