GAMMA-RAY LEAKAGE THROUGH A SLIT IN CONCRETE SHIELD.

An experimental study was performed on γ-ray leakage through a slit in a concrete shield. The work was undertaken at the JRR-4 dry shielding test facility, as part of a series of mockup tests for the first nuclear ship of Japan. The paths of the slits through the shield were either straight or cranked. In the immediate vicinity of the concrete surface, the leakage γ-rays through the slit was seen to contribute a significant portion of the distributed γ-dose rate, but it rapidly diminished with distance from the surface. This was due to the relatively thick shield, in reference to the slit width, adopted in the present experiments, and also because of the strong scattering characteristics of the γ-rays with in the slit channel.The penetration components calculated by the ray analysis method were compared with the experimental results, and it was indicated that this method of calculation should prove useful for making rough estimations of the dose rate distribution of leakage γ-rays.