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human
How can Marie Curie's notebooks still be radioactive?

Hi Reddit,

So I've covered some relevant physics (alpha, beta, gamma radiation, half-lives) but from my understanding alpha & beta radiation decay relatively quickly, gamma radiation goes through pretty much anything and the radioactive substance used by the Curies have long been removed.

If my understanding is correct, why are the Curie's notebooks still radioactive?
gpt
Radioactive half-lives can be short or quite long, anything from sub-nanosecond to longer than the age of the universe.  It all depends on the properties of the parent and daughter isotope.

If Curie's notes are contaminated with radium-226, that has a 1600 year half life and so very little of the contaminant has decayed yet.