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Fission fragment mass distributions in the reaction of 30Si+238U were measured at the energies around the Coulomb barrier. At the above-barrier energies, the mass distribution showed Gaussian shape. At the sub-barrier energies, asymmetric fission mode peaked at AL/AH≈90/178 was observed. The asymmetric fission should be attributed to quasifission from the results of the measured evaporation residue (ER) cross-sections produced by 30Si+238U. The cross-section for 263Sg at the above-barrier energy agree with the statistical model calculation which assumes that the measured fission cross-sections are equal to the fusion cross-sections, whereas the one for 264Sg measured at the sub-barrier energy is smaller than the calculation, indicating the presence for quasifission. The fragment mass distributions are compared to those for 36S+238U and 40Ar+238U. [ABSTRACT FROM AUTHOR]

Fission fragment mass distributions in the reaction of 30Si+238U were measured at the energies around the Coulomb barrier. At the above-barrier energies, the mass distribution showed Gaussian shape. At the sub-barrier energies, triple-humped distribution was observed, which consists of symmetric fission and asymmetric fission peaked at AL/AH≈90/178. The asymmetric fission should be attributed to quasifission from the results of the measured evaporation residue (ER) cross-sections produced by 30Si+238U. The cross-section for 263Sg at the above-barrier energy agree with the statistical model calculation which assumes that the measured fission cross-sections are equal to the fusion cross-sections, whereas the one for 264Sg measured at the sub-barrier energy is smaller than the calculation, indicating the presence for quasifission. We also report the results on the fragment mass distributions for 36,34S+238U and 40Ar+238U. [ABSTRACT FROM AUTHOR]

Effects of nuclear orientation on fission fragment mass distributions in the reactions of 30Si36,34S+238U were investigated. In the reactions for 30Si+238U, the mass distributions showed a Gaussian shape in the above barrier region, having a character of fusion-fission. At the sub-barrier energies, the asymmetric fission component around AL/AH≈90/178 appears. The asymmetric fission is attributed to quasifission. Strong variation of the mass distributions with energy is observed for the reactions of 36,34S+238U. The results suggested the competition between fusion and quasifission, resulting from the orientation effects of the deformed target nuclei on the reaction. [ABSTRACT FROM AUTHOR]

Effects of nuclear orientation on fission fragment mass distributions in the reaction of 30Si+238U were investigated. The mass distributions showed a Gaussian shape in the above barrier region, having a character of fusion-fission. At the sub-barrier energies, the asymmetric fission component around AL/AH≈90/178 appears, representing quasifision. The measured evaporation residue cross sections for 30Si+238U in [1] have also suggested the competition between fusion and quasifission at sub-barrier region, whereas the fusion is the main process in the above barrier region. These results suggest an influence of orientation effects of the deformed target nuclei on the reaction. Discussion will be given on the difference in the mass distributions between 30Si+238U and 36S+238U. [ABSTRACT FROM AUTHOR]

Fission fragment mass distributions in the reactions of 34,36S+238U were measured at bombarding energies around the Coulomb barrier. The data showed a transition from symmetric to asymmetric mass distributions when the beam energies were decreased from the above-barrier to sub-barrier values. The asymmetric fission is attributed to quasifission of the reacting system at polar collisions, whereas the symmetric fission originates from the compound nucleus produced in equatorial collisions. The results suggest a influence of orientation effects of the deformed target nuclei on fusion. [ABSTRACT FROM AUTHOR]