  The smallness of the cross section of evaporation residues formed in the hot
fusion reaction $^{48}$Ca+$^{232}$Th is analyzed by the dinuclear system model
(DNS). The capture probability has been calculated by solving the dynamical
equations of motion for the relative distance between the centers-of-mass of
the DNS nuclei. Fusion of nuclei is considered as evolution of the DNS to a
stable compound nucleus. The fusion probability has a bell-like shape and
quasifission is one of reasons causing smallness of the yield of the
evaporation residues products. Another reason is the decrease of the fission
barrier for the isotopes $^{275-285}$Dm related with the shell effects in the
neutron structure. The agreement of the theoretical results obtained for the
yield of the evaporation residues with the experimental data measured in the
Factory of superheavy elements of Joint Institute for Nuclear Research is well.
