The CANDLES Trigger System for the Study of Double Beta Decay of 48Ca

The CANDLES trigger system is used for the study of Double Beta Decay of Ca-48. The detector of this experiment consists of CaF2 crystals as the sources and the detectors, immersed in the liquid scintillator as a 4 pi active shield. Because the decay constant of liquid scintillator (similar to a few 10ns) is a few ten times shorter than that of CaF2 scintillator (similar to 1 mu s), if we trigger the signal by the pulse height, the energy threshold of liquid scintillator lights are a few ten times lower than CaF2's one. High counting rate of the liquid scintillator causes dead time. In order to avoid this problem, we have developed a Dual Gate Trigger. In this paper, we describe the trigger system of the CANDLES experiment and its performance.