it was one of those random, oh, this is how i learned about XYZ moment for me as well. yes, as he states in the video, i could also have read the wikipedia page (and at some point i probably still will), but his explanation went into so much new information for me that it was filled with so many "hmm, never really thought about that to even consider how it worked", but here's the info in a youtube video so now i just have answers to questions i didn't know i had

I saw that and I was like hmm. Scanning electron microscopes have sure advanced a lot since I was a grad student.

Rutherford scattering (backscattering) is proportional to atomic number. Heavier (more protons) atoms scatter more.