The sun emits vast numbers of neutrinos which can pass through the earth with little or no interaction. Solar neutrinos shine down on us during the day, and shine up on us during the night after passing through the earth almost no absorption. About 91% of solar neutrons are produced by the proton-proton fusion to produce deuterium. Neutrinos from the proton-proton fusion have low energy up to 400 keV. The flux of low energy neutrons is about 7 x 1010 neutrinos/cm2s, i.e 70 billion neutrinos per square cm per second. A square centimetre is about the size of your small finger nail. There are several other processes producing neutrinos up to 18 MeV (see figures below).
Background radiation is a natural part of the environment. The largest source of background radiation exposure comes from the natural radioactivity in rocks and soil and the inhalation of naturally occurring radon that seeps from the ground into our buildings. We are also exposed to cosmic radiation and the natural radioactivity in food and in the body. On average, Australians are exposed to about 1.5 mSv each year from natural sources, although for some the dose might be more than double that. On average, we also receive about 1.7 mSv per year from medical diagnoses and treatment.