Other Interesting Aspects of Natural Radioactivity

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Written and developed by Prof. Tor Bjørnstad (IFE/UiO) 

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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 • 105 m3) and the listed activities. It should be noted that activity levels vary greatly depending on soil type, mineral make-up and density (~1.58 g/cm3 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)

>774 GBq (>21 Ci)