How to build and operate a simple mass spectrometer. Please ask questions in the comments, as always. (I had to re-upload this video to fix the ending --I'm very sorry if your early comments were lost!)
Scientific American article: https://www.scientificamerican.com/article/the-amateur-scientist-1970-07/ $7.99 is a good value for the entire back issue in plain PDF format, and an example of a publisher being reasonable. I'm happy to support this.
Original Dewdney paper: https://sci-hub.tw/https://doi.org/10.1119/1.1969211
https://en.wikipedia.org/wiki/Isotopes_of_potassium
https://en.wikipedia.org/wiki/Ionization_energy
https://en.wikipedia.org/wiki/Thermal_ionization
https://en.wikipedia.org/wiki/Gyroradius
https://www.patreon.com/AppliedScience