since wet sand would not flow. During a second injection the apparatus 

 did work reasonably well, and the sand was pumped to the bottom. A third 

 injection was made without the apparatus. 



It was recognized that the hopper had serious faults, and another 

 device was designed and built for use in the December 1967 tests in 

 the Point Conception area. This apparatus resembles a clamshell bucket 

 (Figure 6). However, it works in reverse: loaded with labeled sand and 

 closed at the surface, it is lowered to the bottom where a lever -spring 

 mechanism opens the bucket upon contact with the bottom. On two of three 

 occasions, scuba divers had to manipulate the jaws of the clamshell in 

 order to completely open them. With a capacity of kO liters, it proved 

 effective for placing sand as a point source in water seaward of the 

 breaker zone. 



3. Mobile Detector 



Labeled sediment used in tracing experiments can be studied by making 

 on-site measurements or by collecting samples from the environment which 

 are later analyzed in a laboratory. The latter technique is laborious 

 and time consuming, and could involve problems of radiation exposure. On- 

 site measurements minimize radiation exposure problems and provide data 

 rapidly. Ability to quickly know of the presence or absence of labeled 

 material is an aid in surveying. 



On-site measurements can be made by holding a scintillation counter 

 or Geiger-Mtiller tube against the sediment and obtaining discrete readings 

 Such a technique is usually employed in laboratory experiments, and was 

 used in the experiment reported in Section III. Distances and areas in- 

 volved in most field operations require a mobile detector system with 

 continuous readout of data. Other investigators have reported the use of 

 sled-mounted detectors (Krone, 1960b; Ingram, et al , 1965; Rakoczi, 1963), 

 Such a device has been used with some success in estuaries and protected 

 harbors, although even in these environments the sled has tipped over, 

 disrupting the surveys. Such a system would likely be unstable in the 

 surf zone, and would be totally unsuitable in rocky areas. Both con- 

 ditions exist in the Point Conception study area. The ability to work 

 in surf or topographically rough areas is required for the program to 

 have general application. A ball-like device that would roll along the 

 offshore marine bottom, through the surf zone, and up on the beach was 

 designed and built by ORNL (see Appendix C). The shape of the detector 

 vehicle resembles a cylinder with rounded ends (Figure 7). 



The outer housing of the detector vehicle is constructed of a steel 

 latticework covered by expanded metal reinforced at the bearing surface 

 by stainless steel rods. This design prevents loose stones and other 

 debris from entering the ball and possibly damaging the four 2 x 2-inch 

 cesium iodide crystals housed inside the "ball" (Figure 8). The open 

 latticework permits gamma energy emitted from the radionuclide to pene- 

 trate to the crystals. At the present time, all detectors are operated 

 to see only one isotope (or gamma ray energy) over an area of approxi- 

 mately 2 square feet. The detector housing, suspended from the axle of 



15 



