Ionizing radiation is a type of radiation with enough energy to separate electrons from atoms, thus ionizing them. This includes radiation used to treat cancer, radiation used in some types of medical imaging, radiation from natural radon gas, and radiation released by nuclear weapons and power plants. Examples of non-ionizing radiation include radio waves, light, microwave and radar. Epidemiological studies have shown that certain wavelengths of ionizing radiation can damage DNA and cause cancer.
Leukemia and most solid cancers have been linked to radiation exposure. Most solid cancer data are reasonably well described by linear dose response functions, although there may be a decrease in risks with very high doses. People exposed early in life have especially high relative risks for many types of cancer, and the risk of solid, radiation-related cancer seems to persist throughout life. The National Cancer Institute literature indicates that there are other chemical and physical hazards and lifestyle-related factors that can cause cancer.
Although radiation can cause cancer at high doses and high dose rates, public health data do not absolutely establish the occurrence of cancer after exposure at doses and dose rates below approximately 10,000 mrem (100 mSv). Studies of occupational workers who are chronically exposed to low levels of radiation above normal have shown no adverse biological effects. The Nuclear Regulatory Commission (NRC) accepts the linear non-threshold (LNT) hypothesis as a conservative model for estimating radiation risk. This dose-response model suggests that any increase in dose, however small, results in an incremental increase in risk.
Even so, the radiation protection community conservatively assumes that any amount of radiation may pose some risk of causing cancer and hereditary effects, and that the risk is greater for higher radiation exposures.
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