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The fragment mass yields in fission of 235U induced by thermal neutrons for A=145 - 160 and EK=50 - 75 MeV were measured using a mass spectrometer. The fine structure is observed at A=153, 154 and EK=50 - 60 MeV. The obtained results were described in the framework of a model based on the dinuclear system concept. The analyzed correlation between the total kinetic energy and mass distribution of fission fragments is connected with the shell structure of the formed fragments of fission. From this correlation and the time dependence of the calculated mass distribution of the binary reaction products, one can conclude that the descent time from a saddle point to a scission point for the more deformed fragments is longer than that for fragments of more compact shape.© 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]