FEATURE ARTICLE
Fallout from Nuclear Weapons Tests and Cancer Risks
Exposures 50 years ago still have health implications today that will continue into the future
Steven Simon, André Bouville, Charles Land
Understanding Radiation Dose
Radiation absorbed dose is the energy per unit mass imparted to a
medium (such as tissue). Almost all radionuclides in fallout emit
beta (electron) and gamma (photon) radiation. A cascade of events
follows once tissue is exposed to radiation: The initial radiation
scatters, and atoms in the body are ionized by removal of weakly
bound electrons. Radiation can damage DNA by direct interaction or
by creating highly reactive chemical species that interact with DNA.
The basic unit of the system used internationally to characterize
radiation dose is the gray (Gy), defined as the absorption of 1
joule of energy per kilogram of tissue. (The international system of
units is gradually supplanting the previous system based on dose
units of rad, but conversion is easy: 1 Gy = 100 rad.) For
perspective, it is helpful to remember that the external dose
received from natural sources of radiation—from primordial
radionuclides in the earth's crust and from cosmic
radiation—is of the order of 1 milligray (mGy, one-thousandth
of a gray) per year; the dose from a whole-body computer-assisted
tomographic (CT) examination is about 15-20 mGy, and that due to
cosmic rays received during a transatlantic flight is about 0.02 mGy.
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