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when they use gamma rays to sanitize hospitals, what happens to the gamma rays after they're done and turn off the whatever they use to produce the rays? do they linger around - but that would harm anyone who walks in the room, right?
Gamma rays, a very high-frequency version of the same sort of radiation as ordinary light, don't linger. When they're absorbed by a material, they deposit their conserved quantities: some energy and a tiny bit of momentum and angular momentum. The gamma ray then no longer exists.
The only really distinctive residue of the radiation is that when the rays are absorbed as rather high-energy quanta, they induce some chemical changes in whatever absorbed them. That should be of little concern in a hospital, because you wouldn't ordinarily ingest the irradiated surfaces.
When gamma rays are used to sterilize food, however, there's some concern about possible chemical degradation of some nutrients. Since the radiation is not left-over in the food, it's not a direct carcinogen. The chemical changes can in principle produce some carcinogens, but other less exotic processes, especially barbecuing and high-temperature frying, are more noted for carcinogen production.
(published on 12/12/10)
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