Novel features of the fragment mass variance in fission of hot nuclei |
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Authors: | W Wagner I I Gontchar A E Gettinger L A Litnevsky H -G Ortlepp D V Kamanin |
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Institution: | (1) Omsk State Railway University, Russia;(2) Forschungszentrum Rossendorf, Institute of Nuclear and Hadron Physics, Dresden, Germany;(3) Joint Institute for Nuclear Research, Dubna, Moscow oblast, 141980, Russia |
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Abstract: | On the basis of data obtained by the incomplete fusion reactions 7Li(43A MeV)+232Th and 14N(34A MeV)+197Au, the energy dependence of the variance (σ M 2 ) of the fragment mass in fission of highly heated nuclei has been investigated for total excitation energies E tot * ranging from 50 up to 350 MeV. The dependence σ M 2 E tot * shows some unexpected features when E tot * exceeds a value of about 70 MeV. After this value, the steady increase of σ M 2 expected from its temperature dependence changes to some kind of plateau between 100 and 200 MeV. Further on, at E tot * in excess of about 250 MeV, the variance is found to increase again sharply. In order to analyze this behavior 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 satisfactorily explains the measured prior-to-scission neutron multiplicities and the experimental mass variances up to E tot * ?250 MeV, but the stochastic treatment does not reveal any increase in σ M 2 at higher excitation energies in contradiction with the data. |
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