Right now, everyone on Earth is bathed in a soup of radioactive energy. Alpha particles, beta particles, gamma rays, muons, neutrinos: The list is long and puzzling, and most of it has nothing to do with human activities.
The average American gets a dose of around 360 millirems of radiation per year—roughly the equivalent of 36 X-rays. About 200 millirems of that comes from radon gas, a colorless, odorless by-product of natural uranium, found in trace amounts almost everywhere. The radioactive decay of radon gas produces alpha particles (consisting of two protons and two neutrons, an alpha particle is just the bare nucleus of a helium atom), beta particles (which are actually fast-moving electrons), and gamma rays (very energetic photons). Radon is not a problem for most people, but in some locations it can accumulate in houses to dangerous levels.
Medical X-rays come in second place, dosing a person with ...
