  Fission-fragment mass distributions were measured for 225,227Pa nuclei formed
in fusion reactions of 19F + 206, 208Pb around fusion barrier energies.
Mass-angle correlations do not indicate any quasi-fission like events in this
bombarding energy range. Mass distributions were fitted by Gaussian
distribution and mass variance extracted. At below-barrier energies, the mass
variance was found to increase with decrease in energy for both nuclei. Results
from present work were compared with existing data for induced fission of 224,
226Th and 228U around barrier energies. Enhancement in mass variance of 225,
227Pa nuclei at below-barrier energies shows evidence for presence of
asymmetric fission events mixed with symmetric fission events. This is in
agreement with the results of mass distributions of nearby nuclei 224, 226Th
and 228U where two-mode fission process was observed. Two-mode feature of
fission arises due to the shell effects changing the landscape of the potential
energy surfaces at low excitation energies. The excitation-energy dependence of
the mass variance gives strong evidence for survival of microscopic shell
effects in fission of light actinide nuclei 225, 227Pa with initial excitation
energy ~30 - 50 MeV.
