The average individual in the United States accumulates a dose of one rem from natural sources every 12 years. The dose from natural radiation is higher in some states, such as Colorado, Wyoming, and South Dakota, primarily because of cosmic radiation. There, the average individual gets one rem every 8 years. Natural background radiation levels are also much higher in certain local areas. A dose of one rem may be received in some areas on the beach at Guarapari, Brazil in only about 9 days, and some people in Kerala, India get a dose of one rem every 5 months.
Many people receive additional radiation for medical reasons.
In 1970, an estimated 212 million X-ray examinations were performed in the United States. The estimated average surface skin dose from one radiographic chest X-ray is 0.027 rem. The estimated average surface skin dose per abdominal X-ray is 0.62 rem. Radiation, like many things, can be harmful. Control of exposure to radiation is based on the assumption that any exposure, no matter how small, involves some risk.