I am familiar with case studies. A single case study is often a curiosity that might motivate someone to do a proper study, but not something from which you can conclude that having Americium in your body is not as dangerous as commonly claimed.

Worst case? What? Those were alpha particles. You're lucky to get them through a postcard.

Which is precisely why you don't want them inside your body, every alpha particle emitted by the delay will hit and be absorbed inside you, it is the worst. That's why the Russian chose Polonium to kill Litvinenko.

There are alpha particles of different energies, and products of decay of emitters may well not be good for your health either. Polonium besides being acutely toxic itself, decays into lead for example.

Alpha particles cannot penetrate intact human skin. But they're extremely dangerous if they're already inside your skin.

I don't know how you can classify that as "worst case exposure".