The present study was intended as a search for sequential fission of projectilelike fragments for reactions induced by intermediate-mass heavy ions. The objective was to determine the fission probability as a function of excitation energy or energy loss in the first step of the reaction. The inclusive charge distributions measured with the large-area ionization chamber for reactions of /sup 58/Ni + /sup 58/Ni at 15.3 MeV/u were found to be dominated by products with Z < 28. Very little yield was observed for nuclei with charges greater than that of the projectile. It has been shown that most of the shift toward lighter products is consistent with the effects of equilibrium evaporation. At the largest calculated energy losses, the inclusive charge distributions were found to be slightly asymmetric due to an increasing component of fragments with half or less of the projectile charge. These light fragments were observed to have much broader angular distributions than the corresponding heavier fragments of the same energy loss. These observations from the inclusive measurements already suggest the occurrence of sequential fission of the projectilelike fragment. More conclusive evidence is obtained from coincidence measurements. Results are presented. (WHK)

In conventional nuclear physics the nucleus is described as a non-relativistic many-body system, which is governed by the Schroedinger equation. Nucleons interact in this framework via static two-body potentials, mesonic degrees of freedom are neglected. An alternative description of nuclear physics in terms of a relativistic field theory has been developed by Walecka. The model Lagrangian containing baryons, sigma-mesons and ..omega..-mesons was subsequently extended to include also ..pi..-mesons and rho-mesons. An essential feature of such a nuclear Lagrangian is its renormalizability. In addition to the description of known nuclear structure the field theoretical approach may reveal entirely new nuclear phenomena, based on the explicit treatment of mesonic degrees of freedom. The existence of such abnormal nuclear states was proposed by Lee and Wick employing the sigma-model Lagrangian. There the non-linearity of the meson field equations allows for soliton solutions in the presence of nucleons, in particular the sigma-field may exhibit a kink. Different types of soliton solutions occur in gauge theories with hidden symmetries. In the phenomenological Lagrangian the rho-meson is described by a non-abelian gauge field, that acquires its mass spontaneously due to the non-vanishing vacuum expectation value of a Higgs field. A general ansatz for soliton solutions of …

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