Volunteers are given tiny traces of a radioactively labelled drug too small to harm them, and typically just one-hundredth of the estimated full dose in a drink.

ECONOMIST: Monitor

The federal government has insisted ever since the TSA decided to install 300 full-body scanners, or strip searchers as critics call them, that getting a small dose of radiation is safe.

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Calabrese says that many poisons follow, instead, a U-shaped curve: The death rate goes down as the dose climbs from zero to a certain small amount, what you could call the optimal exposure.

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