packaging and shipping costs should not increase the total cost to more than 

 $500, The expense involved in a normal 50-hour test which requires approximate- 

 ly 15 working days to complete is of the order of $4,000. This figure includes 

 plant rental, power and labor charges. Thus for an increase in cost of $500. 

 to the normal cost of $4,000 a labelled sediment may be added to a test. The 

 figure appears most reasonable. 



The choice of a specific isotope depends upon the purpose and the length 

 of the test. Generally if a test were to last 2 or 3 calendar weeks (5 working 

 days per calendar week) then optimum half life would be respectively 17, 31 and 

 65 hours. In this fashion it would be possible to detect the radioisotope for 

 the duration of the test and approximately one week later the activity would 

 have essentially disappeared by normal decay. The exception to the above state- 

 ment is that as the test period increases in time and consequently the desirable 

 half life also increases it takes longer for the remaining activity to decay to 

 negligible amounts. Table 1 lists those radioisotopes which appear feasible 

 for testing programs of 1, 2 and 3 weeks. 



TABLE 1 



Isotope 



Numbers 



Numbers 



Gallium 



31 



72 



Sodium 



11 



24 



Praseodymium 



59 



142 



Lanthanum 



57 



140 



Gold 



79 



198 



Half Life Radiation Energy 



in Hours Beta Gamma 



14.3 3.15,2.52,1.5, 0.84,0.6-2.51 

 0.9,0.6 



15.0 1.39 1.37,2.76 



19.2 2.15,0.64 0.135,1.59 



40.0 1.32,1.67,2.26 1.6,0.093 -3.0 



64.6 0.963 0.41,0.68,1.1 



The safety consideration is probably the single most important factor 

 of the design of any test utilizing radioactive material. While detailed 

 safety considerations do not fall properly within the scope of this paper, the 

 importance of the subject does justify some comments upon hazard evaluation. 

 In any testing program which might be considered, several factors tend to 

 reduce any potential hazard. Assuming a total activity of 50 millicuries 

 were to be used at the beginning of the test and that this radioactive material 

 would be homogeneously dispersed over an area of some 30 to 50 square feet, 

 the activity per square foot would be approximately 1.66 to 1.0 millicuries 

 per square foot. The greatest portion of this activity would have shielding 

 above it, that is the water layer which would cover the natural sand bottom 

 under the conditions of the test. As the model beach is subjected to the 

 action of the waves there would be a relatively rapid dispersal on the active 



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