and Putman, Smith and others used glass as a carrier in England. Steers 

 and Smith utilized cement to simulate pebbles and Arlman, Santema, and Svasek; 

 and Arlman, Svasek and Verkerk mention the use of zeolites to simulate sand 

 which becomes activated through ion-exchange techniques. 



When using some material to simulate the natural sediment it is required 

 that the material possess the physical and chemical characteristics of the 

 natural sediments and, also, that this simulated material react in the same 

 fashion as do the natural sediments to the wave and current energy affecting the 

 particles. These criteria may be broken down as follows: 



a) The density of the particles must be the same as that of the 

 natural sediments (excluding the presence of heavy minerals normally found in 

 natural sediments), 



b) The particle size distribution as determined hydraulically should 

 be the same as that of the natural sediments, 



c) The shape of the particles (the roundness and sphericity) should 

 closely simulate that of the natural particles, 



d) The hardness of the simulated sediments should be the same or 

 nearly the same as that of the natural particles, 



e) The chemical properties of the simulated sediment should be such 

 that there is no reaction between the artificial carrier and sea water nor with 

 those sedimentary particles normally present. 



Glass appears to possess all of the necessary characteristics. A boron 

 free soda-lime-silica glass with lead added to obtain the proper density could 

 be used as both the carrier and radioactive tracer. The sodium (Na 24 ) has a 

 half life of 15 hours and is applicable as will be shown later. It is also 

 possible to consider a high silica glass, again with lead added to obtain the 

 proper density, and the addition also of some small percentage of the tracer ele- 

 ment directly to the glass prior to melting. In this fashion a homogeneous 

 glass with density 2.65 or 2.66 grams per cubic centimeter may be achieved in 

 which the tracer element is completely and uniformly dispersed throughout the 

 glass. Grinding the glass will produce particles with low sphericity and round- 

 ness, but it is believed that passing the particles over a flame will cause both 

 roundness and sphericity to increase and thus satisfy the shape requirements. 

 The particle size distribution of the glass can be controlled very closely prior 

 to its irradiation such that the simulated sediment will be identical with, 

 within experimental error, the natural sediment. Finally the glass is sufficient- 

 ly inert chemically to cause no problem. 



The choice of label, the element incorporated in the glass which is to be 

 detected, is dependent upon a number of factors; these are the type of emission, 

 the energy of the emission, the half life, the chemistry of the element and 

 the expense of preparation. The optimum radioactive label is one which may be 

 easily detected and which will last long enough for the purposes of the experi- 

 ment or test. Under the conditions of the test, briefly described earlier, it 

 is necessary that the radioisotope emit gamma photons rather than alpha or beta 



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