NBCO films, prepared by pulsed laser ablation, were irradiated by 200 MeV A
u ions. The magnetization curve shows a shoulder/fish tail peak effect (FTP
E) in the irradiated film while the pristine or as-grown film does not have
any such signature. The absence of FTPE in the preirradiated film and its
appearance in the postirradiated film are explained in the context of compo
sitional variation of spatial density of defects and the concomitant vortex
mobility.