  We have measured the dynamics of individual magnetic fluxoids entering and
leaving thin film, photolithographically patterned rings of underdoped
high-temperature superconductor BSCCO using a variable sample temperature
scanning SQUID microscope. These measurements can be understood within a
phenomenological model in which the fluxoid number changes by thermal
activation of a Pearl vortex in the ring wall. We place upper limits on the
"vison" binding energy in these samples from these measurements.
