Math GFS topic 9th grade e.g. C-14 method?

I'm doing my GFS in math this year. In our textbook (Lambacher Schweizer BaWü) there was a topic called the C-14 method, which I really liked. I've registered that as my topic now. The GFS has to be at least 15, preferably 20, minutes long, and I explained the C-14 method in 5 minutes, or if I go into a lot of detail (e.g., with the discovery of Ötzi), a maximum of 10 minutes. Does anyone have any ideas for a related topic, e.g., something to do with half-life, that I could supplement my GFS with.

Thank you very much