Where do the Geiger tubes of the Museum's detector come from?

They are SBM20 model Geiger tubes (1).

These tubes are of military origin, having been manufactured for radioactivity counters of the army of the former Soviet Union. These tubes, which were mainly purchased in Ukraine and were not very expensive, are known among amateurs for their relative quality and their high reliability and robustness.

_{(1) All data and images of the tubes can be found at http://www.gstube.com/data/2398/}