Inspired by a thread about the SL-1 Reactor accident, I’m left wondering…How do things become “Contaminated” by radiaiation? In fiction and in the news, I’ve heard of normally non-radioactive objects becoming contaminated from nuclear accidents/explosions/waste, but I don’t know how this “works.” Do contaminated things become coated or infused with bits of radioactive material, or are they somehow becoming radioactive themselves? The way I often hear the subject described, it sounds like nuclear “cooties.”
I mean, the SL-1 incident, for example, even human corpses were contaminated. But, surely if you were to just stick a cadaver under an X-Ray machine for a few days, you wouldn’t make the flesh and bone “radioactive”…or would you?
Ranchoth
Both things happen: Objects become physically dusted with radioactive particles that continue to radiate, making the item radioactive until cleaned (hence the high-pressure hoses used around bomb sites), and atoms subjected to radioactive bombardment can transmute into radioactive isotopes, which then proceed to radiate (for example, a stable piece of Cobalt-59 will turn into the radioactive Cobalt-60 if exposed to neutron bombardment).
Contamination is a problem in the nuclear energy world, leading to many pounds (tons?) of what’s known as low-level waste (gloves, pieces of glass, etc., that are mildly radioactive from being in close contact with radioactive materials), which must be safely disposed of (typically in a deep ditch away from groundwater, IIRC).
I believe that most of the problem of contamination is due to “dusting” with radioactive materials. This is especially a problem with fallout – bombs set off in the earth or slightly above it produce huge amounts of highly radioactive material, and some of the material produced has a very long half-life and may (like strontium-90) have an affinity for certain organs, causing them to concentrate there. The Castle Bravo test produced a lot of fallout, and it contaminated the deck of the Japanese fishing ship Fukuryu Maru and its catch. The Sedan test in the Nevada desert was a shallow burial, deliberately done that way to test excavation capabilities of bombs, and I believe it’s still extremely radioactive.
The other kind of “contamination” is activation, where intense bombardment produces radioactive isotopes. You won;t get this to any reasonable degree with exposure to fallout particles, only from the initial flood of radiation from the blast, and only close by the site. A lot of the isotopes so produced are very short-lived. It’s the longer-lived stuff in the form of fine particles (the fallout) you have to worry about.
Re activation: I recall reading of an example from early nuclear tests, where defunct battleships were moored near the blast to see the effect. On exploration of one ship, a very high count was found coming from a cake of soap, whose sodium content had been converted to a radioactive sodium isotope.
For activation, you need neutrons which are produced either by a bomb, in a reactor, or in a linear accelerator. The neutrons are absorbed by the nuclei of the target material and are changed into a radioactive isotope of the material. Looks the same, smells the same, but it’s radioactive until it decays to a non-radioactive deacy product.
One of the reasons that commercial nuclear reactors create radioactive waste is because the water flowing through piping and valves causes small pieces of metal (wear products) to be introduced into the cooling water for the reactor. These wear products pass throught the reactor, are activated and subsequently settle out in lower flow areas of the cooling system, producing hot spots. During plant outages, we try to flush out these hot spots into our radioactive waste treatment facility so the workers get less radiation exposure from them.