Scintillation counter, segmented shield

Claim 1

In a scintillation counter having a sample-receiving zone within a massive lead radiation shield, at least one photomultiplier tube assembly responsive to light scintillations produced from radiation emitted by said sample, said tube having an elongated shape and being removably contained within said shield, the improvement whereby said lead radiation shield is disassembleable into a plurality of segments to allow installation and removal of said photomultiplier tube, and which segments, when assembled, prevent straight-line access of external radiation through said lead shield into said samplereceiving zone or into said assembly, comprising: a sample-zone-surrounding segment having an axial cylindrical bore sufficiently large in diameter to receive one section of said elongated photomultiplier tube assembly, an intermediate segment having an axial cylindrical bore coaxial with said sample-zone-surrounding segment for receiving a second section of said photomultiplier tube assembly, said intermediate segment being longitudinally divided into two segments for radial outward movement of each segment to permit access to said second photomultiplier tube assembly section, and an end cap segment covering the bore of said intermediate segment, the parting surfaces of said segments thereby having no surfaces offering straight-line access of external radiation through said lead shield into said sample-receiving zone or into said assembly.