Natural radiation
...
discusses how doses from natural sources of radiation in our environment are
controlled.
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 radiation
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.
