Transient times of fission inAr40+232Th peripheral collisions

Peripheral ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$ ${+}^{232}$Th collisions at a bombarding energy E/A=30 MeV were studied by measuring coincidences of fission fragments with projectile fragments detected near the grazing angle. It is found that the sequential fission of the highly excited target residue nuclei is severely hindered if their excitation energies, determined from the measured recoil momenta, exceed a value of abour 50–75 MeV. A transient time of fission of the order of ${10}^{\mathrm{-}20}$ s is deduced.