Magnetic fluids consisting of magnetite nanoparticles and a surrounding bilayer of a primary and a secondary fatty acid surfactant were prepared using either 10-undecenoic acid or undecanoic acid for one or both of the surrounding layers. The olefin units were included within the structure as sites for polymerizing the shell components and increasing the stability of the magnetic fluid. In our experiments, we exposed the magnetic fluids to various levels of gamma irradiation and observed that the position of the unsaturated fatty acid in the bilayer affected their extent of polymerization, as evidenced by IR and NMR spectroscopies. When 10-undecenoic acid was used solely for the primary layer, gamma irradiation resulted in only 50% conversion of the olefinic groups; however, their complete conversion occurred when 10-undecenoic acid was used as both the primary and secondary surfactants of the bilayer. Light scattering measurements showed that this latter magnetic fluid displayed a significant improvement in stability after irradiation on dilution with water. Gel permeation chromatography provided a measure of the aggregation number for the polymerized surfactant shell within these various fluids and showed that the polymerization process was affected by the irradiation dose as well as by the inclusion of the unsaturated surfactant as either the primary or secondary layer or as both layers of the bilayer coating.