After watching an episode of NOVA on PBS, it occurs to me there have been quite a few atomic bombs set off over time. Each created a lot of radioactive material. Many were set off above ground, unleashing the material into the open air.
Presumably the radioactive material had a long half life.
So…where is it all now? How much is in my backyard?
Breathe deeply when you sweep out the garage on Saturday morning.
Some of it, sure. But the most dangerous materials are the ones with the shortest half-life. A short half-life material releases its energy all at once, doing a lot of damage, while a long half-life material does so gradually. So once you wait out the really fast stuff, the rest is a lot less significant.
Apparently, there’s a whole hell of a lot of it out in the Utah desert. The filming of The Conqueror (the John Wayne movie about Genghis Khan) near St. George, Utah, occasioned an astounding track record of cancer in both cast and crew. John Wayne, Susan Hayward, Pedro Armandariz, Agnes Moorehead, John Hoyt and director Dick Powell all died of cancer. By 1980, 90 of the 220 cast and crew had been diagnosed with cancer and half of those had died of it.
It probably didn’t help that most of these people, like many of their generation, were heavy smokers. (Wayne averaged between 3 and 4 packs a day during most of his adult life; that’s about one evey 12-18 minutes.) Exposure to radioactivity might be a contributing factor, but it can hardly be pointed to as the exclusive cause of death.
As for the question by the o.p., Chronos is right in saying that the most dangerous radioactive material was short-lived, and the longer-lived residual products are far outweighed by natural radioactivity from uranium-thorium-radon decay and that created by atmospheric impact of high energy cosmic radiation.
Stranger
It was fun while it lasted…
It is kind of sad really. During the golden era of above-ground nuclear tests ( 
), a large amount of tritium was injected into the atmosphere. It came down quickly in the rain. This water ended up in the ocean. This tritium tracer event is a great tool that oceanographers use to track ocean currents and how fast water moves from the surface to various depths. But it is decaying and getting weaker. So far science has not been successful in convincing the world to inject another big pulse of radioactive fallout into the atmosphere. Sigh.
[The above is true-except that I have never heard of any oceanographer wishing for more nuclear tests to continue the experiment.]
I’m never sweeping out my garage again!
So is Hiroshima completely safe to live in now? I know people live there but is it safe? 60 years doesn’t sound like much in terms of radiation half-life.
The scuttled wrecks of Scapa Flow: Scuttling of the German fleet at Scapa Flow - Wikipedia
It can go a lot further than that. Neutrino detectors are shielded in part by lead salvaged from the ballast of sunken galleons, which have been at the bottom of the ocean for centuries. Not only has it been protected from man-made irradiation for that time, but also from cosmic rays, leaving it the least radioactive lead available in the world.