Method of maintaining temperature of irradiation specimen at constant level by using partition plate as heat-generating plate

The present invention concerns a method of maintaining the temperature of irradiation specimens at a constant level during irradiation. Water supplied is caused to flow downward between the outer wall of an irradiation device and a partition plate. The supplied water is caused to flow upwardly after passing through the lower portion of the partition plate. Then, the supply water is brought into contact with the irradiation specimen when it is turned into an uprising stream. The thickness of the partition plate is made larger than usual. Thus, the partition plate is heated by gamma-ray to function as a heat generation plate and heat the supplied water flowing outside of the plate. Further, the heat flow from the inside to the outside is reduced. Accordingly, the specimen can be maintained at a predetermined temperature. (K.M.)