I understand that generally, the heavier an element is, the less stable its nucleus, but why are promethium and technetium still quite radioactive, despite being nowhere near where the stable elements pretty much end?
In: Physics
The bigger the atoms the more neutrons have to be in their stable forms. The problem is that there have to be a whole number of neutrons an protons. This means that for some atoms the stable isotope is in between two possible isotopes. If you draw out the half life of each isotope you will notice that stable isotopes follows a non-linear line and that the half life for the isotopes along this line goes up and down as it gets into and out of phase of the whole number of neutrons in the isotope. There are even stable phases within heavy elements but it becomes harder to synthesize the correct isotopes the bigger the atom is.
But there are still no isotopes that is not radioactive at all. All particles will decay at some point. We have yet to measure the half life of protons but every model we have say it should be radioactive like the other particles. So while elements like Technetium and Promethium are more radioactive then other similar atoms but they too are radioactive.
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