Novel Features of the Fragment Mass Variance in Fission of Hot Nuclei


Novel Features of the Fragment Mass Variance in Fission of Hot Nuclei

Wagner, W.; Gontchar, I. I.; Gettinger, A.; Litnevsky, L. A.; Ortlepp, H.-G.; Kamanin, D. V.

Basing on data obtained by the incomplete fusion reactions 7Li (43 AMeV) + 232Th and 14N (34 AMeV) + 197Au, the energy dependence of the variance of the fragment mass in fission of highly heated nuclei has been investigated for total excitation energies ranging from 50 up to 350 MeV. This dependence shows some unexpected features when the total excitation energy exceeds a value of about 70 MeV. After this value the steady increase of the variance expected from its temperature dependence changes to some kind of plateau between 100 and 200 MeV. Further on, at energies in excess of about 250 MeV, the variance is found to increase again sharply. In order to analyze this behaviour quantitatively, a dynamical stochastic model has been developed. The model employs the one-body dissipation mechanism and describes the decay of highly excited and rotating nuclei by fission and light particle evaporation. It satisfactory explains the measured prior-to-scission neutron multiplicities and the experimental mass variances up to an energy of about 250 MeV, but the stochastic treatment does not reveal any increase at higher excitation energies in contradiction with the data.

Keywords: nuclear reactions 7Li (43 AMeV) + 232Th; statistical model; dissipation mechanism; nuclear friction; stochastic equation; mass distribution of fission fragments; 14N (34 AMeV) + 197Au

  • Jadernaja Physika 2002, Vol. 65, Nr. 8, pp 1-8

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Publ.-Id: 3265