As one beautiful image is better than many words and as I have zero artistic skills (special thanks to @robotics101 for reminding this to me), I am afraid that the only image illustrating this will be the one provided below (my poor readers…).

That is not what I've said !! But it must be difficult to have great artistic skills and great physics jokes (plus an amazing talent for physics vulgarization and clear illustrations)!

The experimental confirmation of the existence of the muon neutrino involved the production of the first beam of neutrinos ever. This beam was prepared by firing accelerated protons onto a fixed target. The particles produced in that reaction were then flying further away, over tens of metres, before decaying. The associated decay products were finally stopped by a 13.5-metre-thick wall of steel.

I like the idea of "Let's beam a big chunk of metal and see what comes through" ^^