Say some maniacal world leader finally hits the big red button. Or maybe a terrorist takes out the local nuclear reactor. You survive the initial attack, and you’re left to endure a world poisoned by nuclear radiation. How’s that gonna feel?

Measure the dosage

When nuclear reactions get going, they spit out particles with enough energy to rip electrons off of atoms or molecules. The altered bonds produce ion pairs that are extremely chemically reactive. This is known as ionizing radiation, and it’s where the problems start.

There are many types of ionizing radiation. Take your pick from cosmic, alpha, beta, gamma or X- rays, neutrons, or from a handful more. What really matters is how much an organism is exposed to—a concept called absorbed dose.

One way to measure absorbed dose is in units of Grays (Gy). Another common unit is the sievert (Sv), which takes the Gy measure and multiples it by the type of radiation to calculate the effective dose in living tissue. The average radiation exposure during a couple of seconds of an abdominal X-ray is 0.0014 Gy—it’s a light dose, and it’s locally administered, so it’s not that bad. When you really get into trouble is with whole-body exposure, like, say, in the Chernobyl control room immediately after the explosion. There, you would soaked up 300 Sv per hour. But you wouldn’t last an hour. The dose would be lethal in just 1-2 minutes.

via What Nuclear Radiation Does To Your Body.