Other Interesting Aspects of Natural Radioactivity
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Natural Radioactivity in Soil
How much natural radioactivity is found in a volume of soil that is 1 square kilometer, by 50 centimeter deep? The following table is calculated for this volume (total volume is 5 • 10^{5} m^{3}) and the listed activities. It should be noted that activity levels vary greatly depending on soil type, mineral makeup and density (~1.58 g/cm^{3} used in this calculation). This table represents calculations using typical numbers.
Average Natural Radioactivity in an upper crust volume corresponding to one square kilometer by 50 cm deep, data taken from the table next page. We suppose equilibrium between 238U and 226Ra and an emanation factor of 222Rn of 0.5.  
Uranium 238 
36 Bq/kg (1 pCi/kg) 
1500 kg 
28 GBq (0.78 Ci) 
Thorium 232 
44 Bq/kg (1.2 pCi/kg) 
7900 kg 
34 GBq (0.93 Ci) 
Potassium 40 
850 Bq/kg (23 pCi/kg) 
2528 kg 
670 GBq (18 Ci) 
Radium 226 
36 Bq/kg (1 pCi/kg) 
0.78 g 
28 GBq (0.78 Ci) 
Radon 222 
28 kBq/m3 (0.76 nCi/m3) 
2.4 µg 
14 GBq (0.38 Ci) 


Total: 
>774 GBq (>21 Ci) 