State-of-The-Art Photomultipliers for Anger Cameras

A study was conducted to determine the state-of-the-art in PMT's (photomultiplier tubes) used in Anger scintillation cameras. These are end-window PMT's with transmission-mode photocathodes. Several hundred PMT's including venetian blind, box-and-grid, "tea-cup" and "gamma target" types were selected from a population of 20 000 and carefully studied. Typically the sample size for any given type exceeded 100. The best observed 57Co PHR (pulse height resolution) values were 8.0% for a two-inch PMT with box-and-grid dynodes and 8.6% for a three-inch PMT with venetian blind dynodes. No one multiplier structure was found to be superior overall. It was concluded that a small number of PMT's out of the typical population exhibit exceptionally good PHR, indicating that better PMT processing control coupled with new designs could improve the relative 57Co PHR average by as much as 10 to 20 percent. The impact of this potential improvement upon Anger camera performance is discussed.