Determining the Composition of Radioactive Hotspots in the Third Phase of SNO

The third and final phase of the Sudbury Neutrino Observatory (SNO) was distinguished from earlier phases by the addition of 40 $^3$He-filled proportional counters. Despite great efforts to ensure the cleanliness of construction and installation, early analysis of Cerenkov light revealed three radioactive hotspots on the proportional counter bodies. We present two new methods employed to determine the composition and activity of these spots and their contributions to SNO's solar neutrino neutral-current interaction backgrounds.