New Phenomenon Observed in Thermal Release of ^sup 99m^Tc from Molten ^sup 100^MoO^sub 3

99mTc for medical use can be separated by thermochromatography from molten 99MoO3. The effect of moist oxygen gas on the 99mTc release from molten 99MoO3 was investigated using a 99Mo/99mTc generator. 99Mo was produced from the reaction of 100Mo(n,2n)99Mo. A new phenomenon was observed: the release rate and the separation and the recovery efficiencies of 99mTc were higher in the moist oxygen gas than in the dry oxygen gas. The present result is a significant development towards the stable production of high quality 99mTc from molten MoO3 with high separation efficiency. The result also provides us a new insight into the interaction between the moist oxygen gas and the molten MoO3.