Gamma counter apparatus

Claim 1

A gamma activity counter apparatus for use in automated radioimmunoassay systems which comprises a scintillator counter comprising two photomultiplier tube assemblies, each assembly having a scintillator crystal having a sample receiving zone extending vertically therethrough and a photomultiplier tube, the tube being in light-transmissive relation with the scintillator crystal and each crystal being in gamma-transmissive relation with the sample receiving zone therein; a lead radiation shield encasing said photomultiplier tube assemblies, said assemblies being removably contained within said shield and being so positioned therein that each assembly abuts upon the other, and having bores extending upwardly through the radiation shield in alignment with, and communicating with the sample receiving zones; means for lifting into said sample receiving zones a pair of sample carriers from a carrier holder disposed directly beneath and in alignment with said sample receiving zones and for lowering the pair of sample carriers; and means for incrementally and continually advancing said holders into position beneath and in alignment with said sample receiving zones, such that each incremental advance moves the holder the distance of two sample carrier spaces, where for each counting period, for any series of an even number of sample carriers, the first and the last in the series are lifted into said scintillator counter for simultaneous gamma activity counting.