The Earth has been naturally radioactive since its formation. This natural radioactivity is found in the soil, rocks, air, and food, generating internal heat and contributing to environmental radioactivity.

12 1

18 0

7 0

6 0

12 0

25 2

23 1

22 2

5 0

24 1

33 2

15 0

14 2

2 0

21 4

15 2