> I'm also not sure where you got the idea that alpha emitters are the worst kind of radioactive substance; alpha radiation is easily shielded.
Ahah! I considered making an appendix especially for this one because I expected some people to make this mistake, so here we are. Notice that if you're French, the mistake isn't yours but it's the official physics course for French high-schoolers which is to blame.
First of all, alpha rays are helium nucleus, they are really heavy compared to electrons (beta rays) and thus, much more energetic (energy of an order of magnitude of a few MeV vs hundreds of keV), and gamma rays in the case of radioactivity are even lower (40 keV in case of iodine for instance).
If you stand in front of a radioactive source, the radiations comes from in front of you, you can really easily shield against alpha rays (because they are big!), but you can't really shield against gamma rays (because they are just photons), then gamma rays are the most dangerous in that specific context.
But most people aren't physicists or nuclear workers, and you don't usually end up being irradiated by a radio source (the incident you talked about earlier is a good counter example though). The major risk faced by a population is not direct irradiation, it's contamination: that means, you eat food or drink water which contains some radioactive element. And now you get the radioactive source right in your body (let say the thyroid, if we're talking about radioactive iodine). Here, there is no possible shielding, so the total energy is what matters. And regarding the different kinds of rays and their ability to pass through matter, gamma rays have some chance to exit your body without ionizing a single cell, beta have less chance, and alpha have zero chance to go out.
So yes, in terms of radio protection of populations, you fear alpha rays way more than others. And if you operated a plant you are actually allowed to release a little (and subject to regulations of course) amount of beta-emitters (tritium is released in low quantities quite often for instance) but you aren't allowed to release any single atom of alpha emitters.
Also, the list you quote contains fission products (from krypton to C14) as well as activation products. Under normal conditions (I mean, no critical accident like TMI, Chernobyl or Fukushima), most fission products stays in the fuel rod, and then they won't remain in the decommissioned plant.
Zn65 and Fe59 decay quickly, Tritium will be slowly released in the water nearby (yes, that's the normal procedure and it's happening during all the plant's life) and then you have Co60.