Temperature dependence of a large liquid scintillation detector efficiency

Results of investigating the effect of temperature on the properties of a scintillation detector composed of 150-litre container filled with a white spirit liquid scintillator and a FEM-49 photomultiplier are presented. The investigation of the temperature variation effect on the FEM-49 photomultiplier show the amplification dependence on temperature to be about or less than 0.07% in the temperature range from 10 to 40 deg C. The temperature dependence of the detector efficiency has been measured by two independent methods: according to the anode current of the FEM-49 photomultiplier and the counting rate of cosmic M-mesons. The counting rate of one layer of the operating telescope with area of about 12.5 m2 has been assumed to be ''absolute'' value of muon intensity. The mean values of the efficiency temperature coefficient obtained as a result of measurements for three standard detectors are presented. From the obtained results one can draw the following conclusion: in facilities designed for measurements with a statistical accuracy of an order of the tenth part of percent, it is necessary to stabilize temperature (ΔT (<=) 1 deg C) or to introduce corrections accounting for the detector temperature dependence