W. W. Wilcke

Neutron emission in the reactionHo165+Fe56atElab=8.5MeV/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.

Bombarding-energy dependence of theBi209+Xe136reaction

A previous study of the strongly damped reaction /sup 209/Bi+/sup 136/Xe at 1130 MeV has been extended to the lower bombarding energy of 940 MeV. With the same experimental technique, angular, energy, and atomic charge distributions and their correlations have been measured. The angular distribution of the reaction products is sideways peaked, but less strongly focused than at the higher bombarding energy. The energy spectrum extends far below the Coulomb energy calculated for touching spherical ions. The charge distributions are Gaussians approximately centered around the initial fragmentation. Examination of the correlations between experimental observables confirms that the energy-loss parameter is the most suitable quantity to describe the time evolution of the reaction. The relationship between energy loss and the width of the charge distribution is studied to gain information on the contribution of the nucleon exchange process to the total dissipated energy. A quantitative analysis establishes the nucleon exchange as theominant mechanism for the dissipation of kinetic energy. A decomposition of the reaction cross section in partial waves is performed. Classical trajectory calculations assuming spherical ions are compared to an empirically determined deflection function, energy loss, and interaction times. These calculations do not provide a consistent description of the experimentalmorexa0» results. From the interaction times and widths of the charge distributions, an angular momentum dependent proton number diffusion coefficient D/sub Z/(l) is derived, which shows a pronounced saturation behavior for angular momenta less than 2/3 of the grazing angular momentum. The total probability for sequential fission of the targetlike fragment is determined to be 30% for all inelastic events. A simple model is presented which allows calculation of this probability on the basis of known fission properties of heavy elements.«xa0less

Bombarding-energy dependence of the /sup 209/Bi+/sup 136/Xe reaction

A previous study of the strongly damped reaction /sup 209/Bi+/sup 136/Xe at 1130 MeV has been extended to the lower bombarding energy of 940 MeV. With the same experimental technique, angular, energy, and atomic charge distributions and their correlations have been measured. The angular distribution of the reaction products is sideways peaked, but less strongly focused than at the higher bombarding energy. The energy spectrum extends far below the Coulomb energy calculated for touching spherical ions. The charge distributions are Gaussians approximately centered around the initial fragmentation. Examination of the correlations between experimental observables confirms that the energy-loss parameter is the most suitable quantity to describe the time evolution of the reaction. The relationship between energy loss and the width of the charge distribution is studied to gain information on the contribution of the nucleon exchange process to the total dissipated energy. A quantitative analysis establishes the nucleon exchange as theominant mechanism for the dissipation of kinetic energy. A decomposition of the reaction cross section in partial waves is performed. Classical trajectory calculations assuming spherical ions are compared to an empirically determined deflection function, energy loss, and interaction times. These calculations do not provide a consistent description of the experimentalmorexa0» results. From the interaction times and widths of the charge distributions, an angular momentum dependent proton number diffusion coefficient D/sub Z/(l) is derived, which shows a pronounced saturation behavior for angular momenta less than 2/3 of the grazing angular momentum. The total probability for sequential fission of the targetlike fragment is determined to be 30% for all inelastic events. A simple model is presented which allows calculation of this probability on the basis of known fission properties of heavy elements.«xa0less

Bombarding-energy dependence of the Bi-209 + Xe-136 reaction

A previous study of the strongly damped reaction /sup 209/Bi+/sup 136/Xe at 1130 MeV has been extended to the lower bombarding energy of 940 MeV. With the same experimental technique, angular, energy, and atomic charge distributions and their correlations have been measured. The angular distribution of the reaction products is sideways peaked, but less strongly focused than at the higher bombarding energy. The energy spectrum extends far below the Coulomb energy calculated for touching spherical ions. The charge distributions are Gaussians approximately centered around the initial fragmentation. Examination of the correlations between experimental observables confirms that the energy-loss parameter is the most suitable quantity to describe the time evolution of the reaction. The relationship between energy loss and the width of the charge distribution is studied to gain information on the contribution of the nucleon exchange process to the total dissipated energy. A quantitative analysis establishes the nucleon exchange as theominant mechanism for the dissipation of kinetic energy. A decomposition of the reaction cross section in partial waves is performed. Classical trajectory calculations assuming spherical ions are compared to an empirically determined deflection function, energy loss, and interaction times. These calculations do not provide a consistent description of the experimentalmorexa0» results. From the interaction times and widths of the charge distributions, an angular momentum dependent proton number diffusion coefficient D/sub Z/(l) is derived, which shows a pronounced saturation behavior for angular momenta less than 2/3 of the grazing angular momentum. The total probability for sequential fission of the targetlike fragment is determined to be 30% for all inelastic events. A simple model is presented which allows calculation of this probability on the basis of known fission properties of heavy elements.«xa0less

Neutron emission in the reaction /sup 165/Ho + /sup 56/Fe at E/sub lab/ = 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.