a *1.37 °" 12.76 



= D 1.37 ♦ D 2 .76 » "IT" 17" 



where D = dose rate at detector ( photons / sec ) 



2 



cm 



1 = detector response (from above) 



—— = surface density of contaminant in 

 photons per unit time from a unit 

 surface area into a unit solid angle 



and O" = activity (in curies) 



2 7f7ZS 



(area of rectangle Xconversion factor cm /ft ) 



After substitution of the proper values and the performance of the indicated 

 mathematics the results are shown below: 



D ~ D 1.37 + D 2.76 = 3 . 841 x 1° 3 + 3.839 x 10 3 



The final calculation of absorbed dose at the detector is made with the 

 following equation: 



Da = ^a E o D 



where D a = absorbed dose 



(j. a = absorption coefficient 



for water (cm /g) 

 B Q b initial energy of photons 

 D = flux from above 



The result of the above calculation may be converted to rad/hr by the use of 

 energy and time conversion factors. Finally the total dose at a point 3 feet 

 above the center of the rectangle is equal to: 



D a = D al.37 + D a 2.76 = 0.0233 rad/hr 



It is also desirable to calculate the dose rate at some position to the side 

 of the contaminated rectangle. This has been done for a detector position 3 

 feet above beach level, 1.5 feet to the side of the rectangle, and 3 feet 

 from the end of the rectangle. The reason this calculation has been made is 

 that this is the most probable position in which a man would be standing during 

 the course of a test. The absorbed dose rate (D a ) in this position is equal to 

 0.01809 rad/hr. The above dose rates appear to indicate that with normal 

 precautions a test of the type suggested above is well within proper safety 

 limits. 



The author gratefully acknowledges the assistance of C. Eisenhauer and 

 J. Hubbell of the National Bureau of Standards without which the above calcu- 

 lation of the absorbed dose rate could not have been made. 



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