The long-term stability and reliability of photomultipliers used in Anger scintillation cameras

A test instrument has been designed to measure the stability of PMTs (photomultiplier tubes) used in Anger scintillation cameras. The instrument is composed of a number of glass capsules containing beta-emitting tritium with a blue phosphor to provide a very stable light source along with a data logger to monitor anode current. Three hundred and sixty PMTs were simultaneously tested for anode luminous sensitivity, dark current, long-term drift rate, erratic gain instabilities, and RMS noise. Results on the use of the instrument to test over 300000 PMTs are discussed, and the impact upon Anger camera reliability is assessed. It is concluded that the use of the test instrument has improved the reliability of the Anger scintillation camera through the elimination of PMTs that could compromise operating reliability. Field service of Anger cameras has been reduced by pretesting and accelerated aging of PMTs before installation into the instrument. The failure rate of PMTs tested by the instrument is less than one in 10⁷ camera hours of operation