discusses how doses from natural sources of radiation in our environment are
Natural ionizing radiation pervades the whole environment. Cosmic rays reach the Earth from outer space. The Earth itself is radioactive. Natural activity is present in food and drink and in the air.
We are all exposed to natural radiation to a greater or lesser extent, and for most people it is the major source of radiation exposure.
Nevertheless, humans, animals and plants have evolved in this background of natural radiation, and the general view is that it is not a significant risk to health — but there are exceptions.
Cosmic rays are mainly protons of uncertain origin in space and very high energies that reach our atmosphere in fairly constant numbers. It is known, however, that some protons with lower energies come from the sun and are given off in bursts during solar flares.
Protons are charged particles, so the number entering the atmosphere is affected by the Earth’s magnetic field — more come in near the poles than the equator — so the dose rate increases with latitude.