The greatest risk of radiation exposure for most people is from radon gas. Radon is part of the uranium decay sequence, and in regions of higher uranium deposits close to the Earth's surface, radon percolates its way up and can collect in basements and tightly-insulated homes. Radiation is a natural part of our environment. Among food items, salad oil is actually very high in radioactive components. Much of the danger from cigarette smoking is due to radioactive isotopes in fertilizers that make their way into the tobacco and then into lungs, where they decay and produce radiation.
German beer contains more radioactive isotopes than American beer.
Possibly the biggest obstacle to interplanetary space travel is radiation poisoning. In order to protect astronauts from the onslaught of cosmic and solar radiation, a prohibitively large amount of heavy shielding would have to be lifted into orbit. This nuclear reactor is not used to produce electricity. By exposing certain substances to neutron radiation, some become radioactive and are then used in scientific studies. Often the isotopes produced have short half-lives.