Stability of positron annihilation lifetime measurement by digital oscilloscopes

Yachi, Hironari; Hashi, Yohei; Hirade, Tetsuya  ; Suzuki, Takenori*

Recently, it is becoming possible to apply digital oscilloscopes for positron annihilation lifetime measurement instead of use of analogue circuit (NIM modules). More than 1 million sets of wave signals from -ray detectors constructed by scintillaters and photomultiplier tubes are recorded by a digital oscilloscope and analyzed afterward by a personal computer. More than 1 million events of positron annihilation are accumulated on a multi channel analyzer (MCA) for 2-4 hours to construct one lifetime spectrum in the case of the conventional analogue lifetime measurement system. However, it is possible to measure 100 times longer time, i.e. to accumulate 100 times more counts, because of the much better stability of the positron annihilation lifetime measurement system by digital oscilloscopes. Although it is clear that the system by digital oscilloscopes is very stable, There is no indication how much it is stable and how we can construct stabler and better systems. We studied these things and can conclude that we should apply one electric power supply for all detectors and higher voltage to the detectors and full range measurement (8bit) can give better time resolution.