My #photomultipliertube test box I made some years ago. Basically a tin box with a lid, made light-tight with adhesive foam made for old SLR cameras. A BNC chassis socket with a bit of coax connects the outside electronics to the voltage divider/socket/PMT.
Shown are the PMT, a test #thallium doped #sodiumiodide #scintillation crystal and a spark gap containing ¹³⁷Cs to generate predictable pulse heights.

#radioactivity #gammaspectroscopy