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The energy spectra of protons and light nuclei produced by the interaction of 4He and 20Ne projectiles with Al and U targets have been investigated at incident energies ranging from 0.25 to 2.1 GeV per nucleon. Single fragment inclusive spectra have been obtained at angles between 25° and 150°, in the energy range from 30 to 150 MeV/nucleon. The multiplicity of intermediate and high energy charged particles was determined in coincidence with the measured fragments. In a separate study, fragment spectra were obtained in the evaporation energy range from 12C and 20Ne bombardment of uranium. We observe structureless, exponentially decaying spectra throughout the range of studied fragment masses. There is evidence for two major classes of fragments; one with emission at intermediate temperature from a system moving slowly in the lab frame, and the other with high temperature emission from a system propagating at a velocity intermediate between target and projectile. The high energy proton spectra are fairly well reproduced by a nuclear fireball model based on simple geometrical, kinematical, and statistical assumptions. Light cluster emission is also discussed in the framework of statistical models. NUCLEAR REACTIONS U(20Ne,X), E=250 MeV/nucl.; U(20Ne,X), U(α,X) E=400 MeV/nucl.; U(20Ne,X), Al(20Ne,X), E=2.1 GeV/nucl.; measured σ(E,θ), X=p, d, t, 3He,4He. U(20Ne,X), U(α,X), E=400 MeV/nucl.; U(20Ne,X), E=2.1 GeV/nucl.; measured σ(E, θ), Li to O. U(20Ne,X), U(12C,X), E=2.1 GeV/nucl.; measured σ(E, 90°), 4He to B. Nuclear fireballs, coalescence, thermodynamics of light nuclei production.
Light-particle accompanied fission is expected to yield results from which one hopes to learn more about binary scission configurations. As a step in this direction, we present a model that allows the calculation of the probabilities with which a given three-particle setup follows from different binary configurations. First results show the workability of the model.
Coupled channel calculations for Coulomb and nuclear excitation of the systems 136Xe-238U and 238U-238U have been performed using the rotation-vibration model. The impact parameter-, energy-and spin-dependence of the excitation probabilities are discussed for the ground state-, β-and γ-band up to Jπ = 36+. It is shown that the energy levels and quadrupole matrix elements are strongly influenced by the rotation-vibration interaction. Analytic expressions for the elastic and coupling potentials are presented.
Quasimolecular resonance structures in the 12C-12C system are studied in the framework of the coupled channel formalism in the energy range Ec.m.=5-14 MeV. The influence of the coupling of the first excited 2+ state in 12C on the resonance structures is investigated by choosing various types of coupling potentials. The intermediate structures in the reflection and transition coefficients and cross sections can be interpreted with the double resonance mechanism. NUCLEAR REACTIONS 12C(12C, 12C), quasimolecular states, coupling potentials, coupled channel calculations for σ(θ).
The theory of direct electron-positron pair production in the collision of heavy ions is formulated in the framework of the quasimolecular model. The pair production process acquires a collective nature for (Z1+Z2)α>1 and can be understood as the shakeoff of the strong vacuum polarization cloud formed in the quasimolecule. The total cross section is, e.g., 76 μb for Pb + Pb at Coulomb barrier energies.