An RCA 6655 photomultiplier tube. This tube, with a nominal diameter of 5 cm, was a 10-stage unit that operated at a cathode-anode voltage of 1250 V. It had an amplification of about one million. These photomultipliers were often coupled to scintillators (plastic or sodium-iodide based), which produced light pulses when struck by gamma rays. The signals, proportional to the gamma ray energy, provided much of the early data on nuclear decay. This particular tube was used for measurements in Bldg. 145 at CRNL. Several thousand, much improved and larger, versions of these tubes were used in the SNO neutrino experiment in Sudbury to look for scintillations in the large heavy-water vessel.
