The radiation circuit (RC) in the IRT reactor of Tomsk Polytechnic Institute went into service in 1967. Analysis of the results obtained during the development and use of earlier analogous installations led to the introduction of a number of important changes in the new model; these increased the neutron-use efficiency and raised the output power with respect to T-radiation. As in the RC of the Institute of Physics of the Academy of Sciences of the Latvian SSR, the T-carrier in the present case constituted an alloy of indium with gallium andtin having the following composition (wt. %): indium 20.5, gallium 67.0, tin 12.5. The tech- nological arrangement of the RC is shown in Fig. 1. In the working mode the T-carrier circulates continuously between the activity generator in the reflec- tor of the and the irradiator situated on the working table in a special "hot" chamber placed in the reactor shielding. A fundamental characteristic of the IRT reactor is the use of a double-layered activity generator. This constitutes two plane coils connected in parallel and lying parallel to each other and to the face of the