10 



Atomic Radiation and Oceanography and Fisheries 



strontium present at a given time is deposited 

 in the sediments in about ten million years. For 

 other elements the residence times relative to 

 strontium are roughly proportional to the trans- 

 fer percentages. Thus they estimate that the 

 residence time for iron is of the order of a hun- 

 dred years. 



Introduction of radioactive materials 



Radioactive materials in large quantities can 

 be introduced into the sea from reactor wastes, 

 from weapons tests, or in warfare. 



gradients of specific activity decreasing from 

 the sites of introduction, and depending on the 

 mixing characteristics of the ocean. 



Nuclear explosions have been the principal 

 source of fission products introduced into the 

 sea to date. The total quantity of fission power 

 from such explosions so far may be estimated 

 at 40 to 60 megatons of TNT equivalent, from 

 the data summarized by Lapp (1956). This 

 corresponds, with 20 kilotons equal to 1 kilo- 

 gram of fission products (Libby, 1956a), to 

 two to three metric tons of fission products. 



TABLE 4 Fission Product Activity After 100 Days Cooling From 10" Megawatt Hours of Nuclear 



Power Production i 



Curies at Specific activity 



Isotope Half-life Tons (metric) 100 days curies per ton 2 



Kr^ 94 y 7.3 3.3 X 10' — 



Sr"* 55 d 86 2.3 X 10'' 0.128 



Sr^ 25 y 463 7.5 X 10'" 0.0042 



Y*° 62 h — 7.48 X 10'" 178 



Y"' 57 d 111 2.8 X lO'' 6,660 



Zr'' 65 d 152 3.2 X 10" — 



Nb"^ 35 d 161 6.3 X lO'" — 



Ru'"^ 45 d 46 1.3 X lO'" — 



Rh"^ 57 m — 1.3 X 10'° — 



Ru'"" 290 d 35 1.5 X 10" — 



Rh'"« 30 sec — 5.15X10'° — 



I'" 8.0 d — 5.2 X 10' 0.0743 



Cs"*' 33 y 705 5.63 X 10'° 20.1 



Ba"' 2.6 m — 5.1 X 10'° 0.728 



Ba"° 12.5 d 2 1.5 X 10" 2.14 



La"° 1.7 d — 2.5 X 10" 595 



Ce"' 28 d 45 1.5 X 10" 268 



Pr'" 13.8 d 2 1.4 X 10" — 



Ce'" 275 d 490 1.6 X 10'° 386 



Pr'" 17 m — 2.4 X 10'° — 



Pm'" 94 y 7.3 3-3 X 10' — 



Sm'" 73 y 0.7 2.0 X 10^ — 



1 Adapted from data of Culler (1954) and Revelle et al. (1955). 



2 Based on tonnage shown in Table 2. 



In Table 4 is a listing of the important fis- The amount of fission products reaching the 



sion products, their half-lives, and the quantities sea from nuclear explosions depends on a num- 



resulting from 10^^ megawatt hours of nuclear ber of factors such as the location of the burst, 



power production (Carritt and Harley, Chapter the distance above (or below) the surface, and 



6). The column "specific activity" shows the the size of the weapon or device. For the 



ratio of the quantity of radioactivity of a par- smaller devices with a TNT equivalent of 



ticular isotope to the total amount of isotopes several kilotons, most of the fallout is immedi- 



of that element in the sea for this amount of ate and local, although an appreciable fraction 



energy. The specific activity will, of course, remains in the troposphere for a few weeks 



be lower for smaller amounts of fission. It is (Libby, 1956a, b). Subsurface explosions will 



also obvious that a uniform specific activity in result in local deposition of a larger fraction of 



all parts of the sea would be obtained only if the fission products; a deep underwater burst 



the fission products were evenly distributed, will deposit practically all of the activity locally, 



Since, under any practical method of introduc- with nearly /, being in the surface layer and 



tion, this will not occur, there are bound to be about § below (Revelle, 1957). In the case of 



