The Why Files The Why Files --

Radiation reassessed

Radiation returns
In 2005, 60 years after the atomic bomb was invented, the specter of ionizing radiation again lurks behind the news:

Dry and desolate desert with mountain in foreground "Dirty bomb" attack: How deadly would the released radiation be?

Nuclear waste burial ground in Nevada: Can it operate safely?

The Department of Energy must jump enormous technical hurdles before opening this repository for nuclear waste in Nevada. Are the radiation exposure standards strict enough? Too strict? It all depends on the real health hazard of low-level radiation. Photo: NRC

Nuclear power: Safe response to global warming and energy shortages?

Depleted uranium weapons: Can they cause cancer?

CT scans and mammograms: Useful medical tools that detect disease with X-rays, or a dangerous source of extra radiation exposure?

Man sits on scanning table as doctors confer nearby.CT scans are a valuable medical tool, but they increase our exposure to ionizing radiation. Photo: Ohio Dept. of Veterans Affairs

The answer to these questions hinges on the health effects of low-level radiation. You would think we'd have a solid answer for that question. Not.

First, some definitions: Ionizing radiation -- alpha and beta particles, and X-rays and gamma rays -- is released by nuclear reactions in bombs, power plants and uranium-bearing rocks (X-rays are also made in medical equipment). Ionizing radiation can turn atoms into charged particles called ions. The electromagnetic radiation made by flashlights, magnets and cell phones cannot do this.

While we know large doses of ionizing radiation can cause disease or kill, the health impact of lower doses is more elusive. You might expect that if a large dose can harm, a smaller dose would be less harmful, but still not safe. Yet all humans are exposed to background radiation (in the United States, the average is 360 millirems per year), from radon, cosmic rays and other sources, and life expectancy continues to rise.

But what happens when we increase the exposure through exposure to medical X-rays, nuclear waste, or depleted uranium weapons? Is there a "safe-enough" level of added radiation, or will any increase above background cause more cancer?

Giant mushroom shaped plume of smoke rises into the atmosphere
August 8, 1945: Smoke rises 60,000 feet above the Japanese port of Nagasaki, after the second atomic bomb ended World War II. Long-term studies of atomic-bomb survivors at Hiroshima and Nagasaki are key evidence on the health impact of low-level radiation. Photo: NARA

It's been 60 years since the atomic bombings of Hiroshima and Nagasaki. What did they teach us about the health effects of radiation?


Megan Anderson, project assistant; Terry Devitt, editor; S.V. Medaris, designer/illustrator; David Tenenbaum, feature writer; Amy Toburen, content development executive

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