Simultaneous measurements of optical absorption, TL, and TSC, for two MgO samples containing 180 and 650ppm Fe, y-irradiated at 14 and 100°C, show the importance of iron in the TL and TSC processes, and indicate that the TSC peaks observed above about 90°C are due to electrons. As in earlier work the red TL emission is observed to be due to Fe2+. With increasing iron content, V-type centres associated with Fe2+play an important role.