Cesium-137, the longest lived by-product of a nuclear explosion, has a half-life of 30 years.
I used to think that meant that for 30 years after a nuclear bomb exploded, everything downwind would be glowing. After a massive nuclear attack, we could count on living underground for at least three decades if we wanted to survive.
Of course the anti-nuke people want you to think that. The truth is not so grim. In fact, even at ground zero, thirty days is enough for all of the most hazardous radioactive isotopes to decay. The ones that are left, well, they don't decay very fast and so they don't radiate as much and are not as dangerous. Get it? So what if you eat a tomato dusted with remote traces of uranium. With a fifty percent chance of it decaying sometime in the next fourteen billion years, what's the chance it will decay in your stomach?
I read an article today that studied the effects from the Chernobyl accident on produce grown in Austria. The plants in Austria picked up radioactive isotopes from the soil from Chernobyl fallout and so were slightly more radioactive than normal. If you ate vegetables grown downwind from Chernobyl in the first year after the accident you got three times the dose you would get if you avoided eating them for one year and then ate them for the next fifty. After the first year, the radiation drops off so rapidly that it takes fifty years to accumulate one third of the dose from that first year.
Got your year's supply?