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Originally Posted by wodin
I'm sorry; I couldn't help pointing out your confusion between radioactivity and ionizing radiation. It’s a common misunderstanding among perhaps 99% of the population. The fact is that radioactivity causes radiation, and it is the radiation that is dangerous (discounting the chemical toxicity of some of the products).
The amount of radioactivity, measured in curies, does not change; however the specific activity in curies per volume does. That is accomplished by dilution, in the case of vitrification, dilution in leaded glass.
Radiation is attenuated by two methods, as you pointed out, one is shielding by massive material, in this case the lead in the glass. The other is distance from the source which, in the case of gamma radiation, obeys the inverse square law that most of us learned about in high school physics class. Classic health physics also lists time, which means to limit the amount of time one is exposed. In this case that is moot.
So, vitrification accomplishes two objectives. The first is it attenuates the radiation utilizing shielding and distance. And second is it provides a chemically and mechanically stable environment to store the stuff.
That’s all fine in the short term, but this stuff lasts for geological periods of time. No matter how well it’s packaged, we are creating poisons that will burden our descendants for hundreds of generations.
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The only part that lasts for geological time periods is Plutonium (Half life of 242,000 years) which can be recovered and used for further nuclear fuel. The vast majority range have half-lives from a few seconds to around 5,750 years (Carbon 14) By the time you get 3-4 half-lives out, it's basically harmless.
Shielding and distance. Gamma rays are absorbed by various materials and re-reradiated as heat, just light sunlight heats rocks. Lead has the highest absorption rate of common materials. Takes about a foot of lead. Alpha particles are just Helium without the electrons, and beta are just high speed electrons.
The real jokers are neutrons. But most radioactive materials don't emit neutrons, and 10,000 feet of rock and salt will stop any of them. Cadmium is an absorber of neutrons, but chemically toxic. You used it with care. (and yes, the old Ni-Cad batteries were real toxic....