those old test sources ,especially the black epoxy sealed ones can leaking after this long time, test this by wipe test !
found the other tread:
nice item ! was there a beryllium window in it? price is :beer:
i can recommend this geiger kit:
Soldered Mygeiger Dosimeter DIY Geiger Counter Kit w USB and SBM 20 STS 5 Tube | eBay
has dead time compensation and tube settings can changed
But only very weak because the radioactive particle and the glowing particle must be together as near as possible...thats why the vintage radium paint was milled very very fine ...nowadays in all vintage clocks the paint is burned out from the alpha emission ..even when you hold strong...