Up to a quarter of that received is due to human activity and originates mainly from medical sources. The nuclear fuel cycle does not give rise to significant radiation exposure for members of the public. Radiation protection standards assume that any dose of radiation, no matter how small, involves some possibility of risk to human health, but this deliberately conservative assumption is increasingly questioned.
Radiation can arise from human activities or it can be from natural sources.
Most of the radiation that people are exposed to is from natural sources. About one quarter of the natural radiation comes from the human body itself. The human environment has always been radioactive. Radiation arising from human activities typically accounts for up to 25 percent of the public's exposure every year. This radiation is no different to natural radiation except that it can be controlled.