[hkwerf]

Back when I was a physics student, I helped engineer exactly this experiment as a off-the-shelf solution for schools as a classroom experiment! We used PMTs mounted on top of coffee cans:

http://kamiokanne.uni-goettingen.de/gb/kamiokanne.htm

The FTL muons produce Cherenkov radiation in the water in the coffee cans, which is picked up by the PMTs.

Using this setup gives a much higher rate, as the surface is much larger compared to geiger tubes. Thus it's possible to quickly capture a sufficient amount of muons.

[beezle]

Memory has faded as it was in the last millenia... junior year physics lab one of the experiments was muon counting. It used two large NaI scintillators covered in foil attached to PMTs with a potential > 10kV. I don't recall exactly how we separated them, probably just some type of stand.