Abstract
Inclusive4He and4H energy spectra and heavy fragment coincidence correlations have been measured for reactions of 7.31 MeV/u238U with238U and−197Au targets. The H/He production cross sections are in the range 15–26 mb, and their emission spectra are very similar for the two systems. The observed strong kinematic shifts with angle are reproduced in shape and magnitude by Monte Carlo simulations of particle evaporation from projectile-like and target-like fragments, indicating competition between charged particle emission and sequential fission. No evidence is found for high energy charged particle emission associated with ultra-highZ composite systems. Heavy fragment measurements indicate an abundance of quasielastic and deeply inelastic reaction fragments, as well as sequential fission of target and projectile nuclei. For238U nuclei, the fission occurs predominantly in an asymmetric mode, reminiscent of fission at low excitation energy. For238+238U reactions in the vicinity of the grazing angle, the frequency of single sequential fission (with survival of the partner fragment) is twice as large as double sequential fission in which both the target and projectile undergo fission. In238U+197Au reactions, the survival probability of the heavy fragments is even greater. The surprisingly high survival probabilities of high-Z fragments imply a preponderance of very soft collisions in these very-heavy-ion reactions, at least at energies not very far over the Coulomb barrier.
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We appreciate the cooperation of the Lawrence Berkeley Laboratory staff in making this experiment possible, particularly H. Grunder, F. Lothrop, J. Alonso, and R. Stevenson. The Super HILAC crew did a fine job in keeping the U beam alive. We acknowledge C. Maples and W. Rathbun for providing 32 channels of multiplexer in the nick of time. The suggestions and assistance of J.M. Alexander, E. Duek, N. Ajitanand, L.C. Vaz, R. Lacey, and G. Peaslee were helpful and appreciated. One of us (D.Ø.E.) gratefully acknowledges a travel grant from the Norwegian Research Council for Science and the Humanities. This work has been supported by the Division of Nuclear Physics, Office of High Energy and Nuclear Physics, U.S. Department of Energy.
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Kaplan, M., Moses, D.J., Eriksen, D.Ø. et al. Light charged particle emission and fission in238U+238U collisions at 1,740 MeV. Z Physik A 313, 31–37 (1983). https://doi.org/10.1007/BF02115840
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DOI: https://doi.org/10.1007/BF02115840