It could happen like this, in a fraction of a second: Imagine hundreds of passengers enduring waves of heat outside Terminal 1 on a busy summer day at Los Angeles International Airport (LAX). They stand in lines that weave down the sidewalk as a minivan approaches the curb, then erupts in an explosion that rips through the crowd and the terminal. An eerie cloud settles over the area. Authorities arrive and determine that the vehicle-borne IED, or improvised explosive device, was packed with cesium-137.

At the same moment, another bomb detonates in New York's Times Square. This time, the device is filled with the radioactive substance americium. 

The material used in both "dirty bombs" was easily obtained. Cesium helps to treat cancer. Americium is found in smoke detectors. What's more, cesium causes cell damage. It reduces the ability to flex muscles because of its chemical similarity to potassium. Americium particles lodge in the bones. Long-term cancers may result.

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