The dose from natural radiation is higher in some states, such as Colorado, Wyoming and South Dakota, primarily because of increased cosmic and terrestrial irradiation. The average individual may receive 1 rem every 8 years or less. However, there are other areas in the world where natural background radiation levels are very much higher. For example, a dose of 1 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 1 rem every 5 months. In addition to natural background radiation, many people receive additional radiation exposure for medical reasons.
Medical exposures are intentional and clearly have defined benefits for the individual.
The estimated average surface skin dose per abdominal x- ray is 0.62 rem. Table 3.2 and Figure 3.1 list annual dose contributions from some of these sources. The percentage contribution of various radiation sources to the total average effective dose equivalent in the U. S. population. The possible annual dose from working 8 hours a day near a granite wall at the red cap stand in Grand Central Station, New York City, is 0.2 rem, and the average annual dose in the United States from consumer products and air travel is 0.0026 rem. Death due to radiation exposure requires high exposures.