It's a Packard 1000 TR Liquid Scintillation Analyzer, which is used to generate a count and energy spectrum from radioactive erm, stuff.
Where this differs is the sample is suspended in a liquid and it's the liquid itself that is the scintillator. The light is then picked up by two photomultipliers. Because the scintillation substance is in contact with or dissolved within it it's more sensitive and accurate.
The seller is quite local to me and dispose of all sorts of IT, medical and science items, in fact it's the same place i acquired the Palflash 500 Flash Light Source.
The guys there had no idea what it was and actually asked me what it's for!
So it's currently sat in the back of my van, there is some serious lead shielding around the analysis chamber and the photomultiplier tubes. Thankfully the lead should be enough to cover the cost of buying it!