Barrier Attenuation of Air-scattered Gamma Radiation

Just inside the 100-ft radius line surrounding the bunker, the ground was shaped to rise up a slight ramp to create a circular-shaped plateau. The angle of the ramp was designed to insure that direct radiation would pass between 1 and 2 ft above the top of the barriers -only air-scattered radiation reached the barriers. Measurements of the attenuation provided by a horizontal barrier were made using detectors placed in a round hole in the ground, topped by the barrier material at ground level. A cobalt-60 point source was placed 100 ft from the hole. Sandbags or lead bricks were placed on the ground about 6 ft in front of the hole. The height of the lead bricks was the same height as the top of the shield. This assured that the shield was exposed only to air-scattered radiation.