112 Atomic Radiation and Oceanography and Fisheries 



little with neutron energy or substitution of activity, the values all represent lower limits 



plutonium for uranium 235. For our purposes, and should be slightly larger. 



the elements of most interest produced by fis- '^9 . 



^ ■' . activity 



sion are krypton 85, strontium 90, and cesium produced 



137, raneine in half-life from 10 to 33 years; ^. . J'y?^^ 



. . ° ^ 1-1 Fission fission 



tritium, which is not a fission product, is also yield (mega- 



of great importance. Measurable additions to Radioisotope Half-life (%) curies) 



,, , f . •,.• ,. ^- r,r, J Krypton 85 10 years 0.24 2 



the geosphere of tritium, strontium 90, and str^^^i^^ ^q 28 years 5.0 15 



krypton 85 have been noted and are discussed Cesium 137 33 years 6.3 16 



in Part IV in connection with general applica- Lj^by (1956a, b) has given detailed discus- 



tions to transfer study phenomena. In this sec- sions of the fall-out patterns of strontium 90 



tion we estimate the total amounts of these and cesium 137, based on the Project Sunshine 



nuclides which have been produced ; these esti- measurements on world-wide samples. Geo- 



mates are also of some interest in connection physically, the most significant finding is that, 



with the magnitude of the disposal problem, as mentioned previously, the residence time in 



both present and future. ^^ stratosphere of material pushed through 



One result of the advent of nuclear fission ^^^ tropopause is about 10 years. The most 



is that all the krypton in the atmosphere has f ^^"^ measurements on the distribution of 



become contaminated with radiokrypton. De fi/sion products from nuclear explosions (Libby: 



Vries (1956) has measured the specific activity ^^^^^^^ before American Association for the 



of atmospheric krypton, taken in March of Advancement of Science, Washington, D.C 



1955, as 25,000 counts per minute per mole. ^^^^^.^^ ^2, 1956) indicate that the amount of 



The activity is due to contamination with kryp- ^^rontrnm 90 scattered over the surface of the 



ton 85, which decays by ^- emission with a ^^'^^ '' "°^ equivalent to an average activity 



half-life of ten years. From DeVries' measure- concentration of about 16 millicuries per square 



ment, we readily calculate that 56.4 moles, or "'^^- ^^ ^^^l^^^^^' ^^^, ^^^"^^ "°7 ^^^^ ^" *.^;^e 



4700 grams, of Kr«^ are now present in the stratosphere is equivalent to another 12 milli- 



atmosphere, and in ignorance of the rate of curies per square mile. The total amount so far 



production, we make only a small error by distributed is thus about 5 6 megacunes of Sr^o, 



assuming this figure as the total amount of °^ ^^''^ ^^.^^^ 2.4 are still in the stratosphere, 



radiokrypton produced and not correcting for ^^^' assuming purely statistical distribution, 



decay. From the fission yield of 0.24 per cent ^,«"^^ ^.3 megacunes have fallen directly into 



c - iu-^ v^4-««„ :t. ^^^J^^r. <-u.«- .^^J 02 <;nr> the sea, while about 0.9 megacunes have fallen 



for this isotope, it appears that some 23,500 , , , r t^ r , • -, 



~ 1 <cnn 1 ^c ^^o■i'^ J ^1 i-^ • ^ u ^ on the land surface. Because of the similar 



moles, or 5500 kg, of U-^^ and plutonium have ,,^,., ,/-. -.i.r r 



J c • • i-u J \- r i-u half-life and fission yield, the figures for cesium 



undergone fission since the advent of anthropo- .,, , , /, '. , °, ^ 



^- r ■ ,,. • ^ , • 137 will be almost identical to those tor stron- 



genetic fission, resulting in an atmospheric . ^ ^ • , r • 1 , 



f • •, f ^ • T. • 1 tium 90. Comparing these figures with the ones 



krypton activity of 2 megacunes. It is assumed, . . . v ^.1.1 0.1. i. ui 



'^ ■' , , ,,,/-• 1 1 given in the above table, we see that roughly 



as seems reasonable, that all fission produced ?^,,-, / 1 r n i.u i-j /: • j Z 



... ' . , \ 5.6/17.4 or -\ of all the solid fission products 



krypton finds its way into the atmosphere. r jju m c • u u j- 



•'^ •' ^ so far produced, by all fission, have been dis- 



From the fission yield data, we calculate the tributed over the atmosphere, the land, and the 



total amounts of radiostrontium and cesium gg^ j^y atomic weapons testing, 



which have been produced; the data for the xhe most important of these elements for 



three elements are shown below. Only the studying mixing rates in the sea should be 



strontium and cesium produced by detonation cesium 137, which being soluble, should be 



of nuclear weapons will escape into the atmos- an excellent tracer for the mixing rate of surface 



phere and be deposited over the surface of the ocean water down through the thermocline. 



earth and sea. Because the krypton figure is Krypton 85 should ultimately prove important 



uncorrected for decay, and because some kryp- for atmospheric mixing studies, especially for 



ton must have gone directly into the strato- comparison of mixing rates of gaseous and 



sphere and is not included in the measured solid elements across the tropopause. 



