Chapter 2 Natural Radiation of Selected Organisms 29 



TABLE 1 Trend of Cosmic Rays with Distance our comparisons the same average radioactivities 



Above and Below Sea Level used by Libby (1955) are used here for granite 



Variation with elevation above sea level, values of ^nd sedimentary rocks, 

 intensity of ionizing component (in mrads/year) 



taken from Libby (1955). , , , f ,• •, 



Internal sources of activity 



Mrad/year 



' --^. — — ' The bodies of large animals contain a much 



Elevation in feet Equator ^'' (mag) higher concentration of potassium than is found 



33 37 in sea water. A value of 0.2 per cent is used 



5,000 40 60 herein for human tissue (Burch and Spiers, 



lO'OOO 80 120 1954) and 0.3 per cent is used for the potas- 



15,000 160 240 • . F ^ ^ ^ J 



2^000 300 450 ^^""^ concentration ot large nsh (Vinogradov, 



1953). Since radio-potassium contributes the 



Variation with depth in water values computed ^^- portion, aside from cosmic rays, of the 



from average attenuation compiled by George (1952) ,. . ,. -u .• . .i j i.^ 



Tuu • u 1 * • * •* c ^\r. o^l radiation contributing to the average dose to 



using Libby s average absolute intensity tor mean sea o o 



level. the total body of any marine organisms, the 



Percent of surface character and distribution of this important 



Depth in meters Mrad/year value natural activity has been compiled in Table 2. 



35 100 



10 10.1 28.8 



20 4.86 13.9 Geometrical factors influencing dose 



50 1.40 4.0 



100 0.47 1.35 A man standing above a granite plane surface 



200 0.15 0.42 receives from the granite roughly one half the 



300 0.074 0.21 radiation which might strike him if he were 



1,000 '.'.'.'.'.'.'.'.'.'. 0^009 ao25 completely surrounded by granite; likewise a 



4*000 .......... 0.007 0.002 man in a row boat receives from the sea only 



one half the dose which the sea gives to any 



compared to that of most natural fresh waters. submerged organism. 



The major activity in sea water comes from Potassium yields both beta and gamma ac- 



radiopotassium (Revelle, Folsom, Goldberg and tivity; roughly three fourths of the total energy 



Isaacs 1955), and only this constituent will be comes from the beta rays. Nevertheless, because 



considered here. Of the metamorphic and igne- of its short range, the beta particle from the 



ous rocks, granite has the highest activity; for potassium in the surrounding sea contributes 



TABLE 2 Potassium Radiation Data 



Distribution and Intensities 



Material Potassium content Beta rays Ga mma rays 



d/m/g mrad/yr d/m/g mrad/yr 



Sea water 0.038% (1) 0.66 2.7 0.068 0.9 



(35%o salinity) 



Man 0.2% (2) 3.5 15 0.36 2.3 (4) 



Fish (large) 0.3% (3) 5.8 24 0.3 3.7 (4) 



Physical Nature of Potassum Activity 



Beta activity = 29 d/s/gram of total potassium 

 Beta ray energy (average) = 0.5 mev 

 Gamma activity = 3 d/s/gram of total potassium 

 Gamma ray energy ^1.5 mev 



Sample Calculations for Potassium Activity 



Beta d/m/g X 1440 X 365 m/yr X 0-5 mev/d X 1-6 X 10^ erg/mev 1000 ^ ^^^^^^^ ^^^^^ ^j^j^j^ ^^^^^^^ 



100 erg/rad 

 to. Beta d/m/g X 4.2 = mrad/yr beta; and correspondingly, Gamma d/m/g/ X 12.6 = mrad/yr gamma. 



(1) Sverdrup, Johnson and Fleming (1942). 



(2) Sherman (1941). 



(3) Vinogradov (1953). 



(4) Assume half of the gamma rays from internal activity are absorbed inside the body. 



