Patent Number: 052176754
Section: claims

1. A process for the synthesis of .sup.11 C-labeled methyl iodide which comprises a .sup.11 CO.sub.2 -producing process of producing carbon dioxide gas labeled with .sup.11 C, a bubbling process of bubbling .sup.11 CO.sub.2 gas into a reducing agent solution in a reaction vessel, a .sup.11 CH.sub.3 I synthesis process of synthesizing .sup.11 CH.sub.3 I from an intermediate produced by a reduction in the bubbling process and a .sup.11 CH.sub.3 I distillation process of distilling .sup.11 CH.sub.3 I synthesized in the .sup.11 CH.sub.3 I synthesis process, and deciding the termination of the bubbling in the bubbling process and the termination of the distillation in the .sup.11 CH.sub.3 I distillation process based on the variation of the radiation emitted from the reaction vessel, which process further comprises a reducing agent solution-removing step of evaporating the reducing agent solution after the termination of the bubbling, and deciding the termination of the evaporation in the reducing agent solution-removing process based on the variation of the temperature in an exhaust tube for discharging the vapor of the reducing agent solution connected with the reaction vessel. 2. The process of claim 1 which further comprises a .sup.11 CO.sub.2 -supplying process of supplying .sup.11 CO.sub.2 gas produced in the .sup.11 CO.sub.2 -producing process to a reaction vessel, and deciding the termination of the supply of .sup.11 CO.sub.2 gas in the .sup.11 CO.sub.2 -supplying process based on the variation of the radiation on the introducing side of .sup.11 CO.sub.2 gas. 3. The process of claim 1, wherein the reducing agent is LiAlH.sub.4. 4. The process of claim 1, wherein the .sup.11 CH.sub.3 I is synthesized by adding hydroiodic acid. 5. Apparatus for the synthesis of .sup.11 C-labeled methyl iodide which comprises: a target box in which .sup.11 CO.sub.2 gas is produced, said target box containing .sup.11 CO.sub.2 gas;  a reaction vessel in which .sup.11 CH.sub.3 I in synthesized from the .sup.11 CO.sub.2 gas produced in the target box, said reaction vessel containing .sup.11 CH.sub.3 I; and  a radiation sensor provided adjacent the reaction vessel to detect an increase in radiation due to the introduction of .sup.11 CO.sub.2 into the reaction vessel upon the synthesis of .sup.11 CH.sub.3 I and to detect a decrease in radiation due to discharge of .sup.11 CH.sub.3 I from the reaction vessel upon distillation wherein said reaction vessel contains a reducing agent solution into which the .sup.11 CO.sub.2 gas is bubbled to result in the synthesis of the .sup.11 CH.sub.3 I, whereafter said reducing agent solution is evaporated to result in an increase in temperature, said temperature dropping upon termination of the evaporation, which apparatus further comprises a temperature sensor for detecting the temperature of an exhaust tube for discharging the vapor of the reducing agent solution reducing the .sup.11 CO.sub.2 gas. 6. The apparatus of claim 5, which further comprises a transfer tube connecting the target box with the reaction vessel and a radiation sensor provided adjacent the transfer tube.