Density Comparison:Uranium (U): ~18.7 g/cm³ Thorium (Th): ~11.7 g/cm³ Lead (Pb): ~11.3 g/cm³ Volume Change Potential: Transition from U or Th to Pb may result in a slight volume reduction due to lower density.
- Volume changes during radioactive decay are typically negligible on the atomic scale and often not measurable in bulk samples unless gas release or phase changes are involved.
- For engineering or nuclear applications, localized swelling or damage due to radiation (radiation-induced defects) can lead to structural changes in materials over long periods.
Do you have a specific material or decay process in mind? That might help narrow the explanation!
The time scale should be better specified in the question !
If you consider a few hours, the number of decaying atoms of the very long lived U or Th is very small, and the volume change of the sample is negligible. But the final product Pb is not yet produced after a few hours, so it is not an answer to the question that refers to Pb.
But if you consider the full decay of these elements into Pb, they will always go through the gazeous state (Radon) and the final situation depends on the capacity of diffusion of radon through the material. It may happen that a large part of radon escapes to the atmosphere (e.g. if the initial material is a powder) and its decay products then deposit here and there on the surfaces, as a very thin layer mixed with other deposits. The notion of their volume is then almost meaningless.
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