Pre- and post-scission neutron multiplicities for the reaction ${}_{}{}^{169}{}_{}{}^{}\mathrm{Tm}$${(}^{36}$Ar,f) at $E_{\mathrm{lab}=205\mathrm{}}$ MeV were measured in coincidence with fission fragments of different masses and total kinetic energies. The mass and total kinetic energy dependence of the total neutron multiplicity as well as the width of the out-of-plane fission fragment correlation angle are well described by evaporation calculations. An average time before scission of several ${10}^{\mathrm{-}20}$ s is deduced from the average pre-scission neutron multiplicity. The mass dependence of the post-scission neutron multiplicity is consistent with an energy division at scission proportional to the mass of the fragments. For the first time clear evidence for an increase in pre-scission neutrons with increasing total kinetic energy values has been observed. Possible interpretations of this unexpected behavior are discussed.

• Received 31 May 1989

DOI:https://doi.org/10.1103/PhysRevC.40.2629