ball contains the radiation detectors and is towed behind an amphibious 

 vessel on a 150-ft-long cable. Operating characteristics were found to 

 be excellent in very rough surf and moderatly rocky bottom conditions . 

 While the detector ball is unaffected by heavy surf, early surveys paral- 

 lel to the beach were limited by the ability of the tow vessel to oper- 



ate broadside to the breakers. Survey tracks were made from ~^5 

 to the beach face to overcome this problem. 



to 90 



The radiation measuring equipment shown in Fig.C-3is an underwater mobile 

 system that can be rolled along the ocean floor, efficiently detect the 

 80-keV gamma rays from Xe, and operate on the beach, in the surf zone, 

 and in the ocean to depths of 200 ft. 



Detector System 



The detector system consists of four 2- by 2-in. sodium-activated cesium 

 iodide crystals housed in 0.030 -in. -thick anodized aluminum cans. These 

 cans are mounted in a l/2-in. -thick stainless steel plate that forms the 

 bottom section of a sealed chamber attached to the axle of the ball. As 

 the ball rotates on the stationary axle, the detectors remain oriented 

 toward the surface over which the ball moves. Since the canned crystals 

 are exposed to the water pressure, a l/2-in. -thick Plexiglas light pipe 

 is used as a pressure barrier (see Fig.C-U.) Photomultiplier tubes and 

 preamplifiers are mounted in the detector chamber and are thus protected 

 from the water and pressure. 



Fig. C-4. Underwater Detector Component 

 C-10 



