When people go for a swim in an ocean they are literally bathing in a sea of natural radiation.
The predominant component of the radiation comes from potassium-40 which is a natural part of the earth’s environment. Tritium, a heavy cousin of hydrogen, and carbon-14 are also sources produced when high-energy protons from space smash into oxygen and nitrogen atoms in the air.
This atmospheric source of ocean radioactivity has worked on Earth for almost three billion years. Along with uranium radioactive decay products, humans live within this natural radioactive background.
