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Date: | Thu, 24 Sep 2020 20:38:50 -0400 |
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>Why does cobalt used in an irradiation process leave no radiation contamination?
The cobalt-60 metal itself is the "contamination", so rather than "handle with care" the warning is "do not handle at all".
One can also make gamma rays with americium-241 (found in smoke detectors), caesium-137 (popular for industrial uses), and technetium-99m (popular for medical work) don't mess with any of them, either.
The gamma radiation that the cobalt-60 gives off is literally photons ... light, so they move at the speed of light, and as they have shortest wavelength, these particular photons have the highest photon energy, packing the most punch.
"Cosmic Rays" are also gamma rays, and they are punching tiny holes through everything all the time. There's nothing we can do about it.
A photon can't be radioactive. It's just an electron, traveling solo. But its velocity (speed of light) and its energy makes it a powerful bullet. You need several feet of concrete to stop gamma radiation.
So, the photon does its damage, and is long gone in the same instant that the damage is done. Every wound is a very tiny and clean one, and you'll never find the bullet. All that is left is the hole.
The old joke is about the freshman asked about the variables in the equation for photo energy:
"E is photon energy, h is Planck's constant, c is the speed of light in vacuum and λ.... is....is..."
"What is it?" asks the tired TA.
"The length of the Planck?" guesses the student.
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