PURPOSE: To accurately detect the radiation of high energy, by locating the ionization chamber and scintillation detector in tandem.

CONSTITUTION: The gas 2 ionized with incident radiation is sealed in the ionization chamber 1, the incident window 3 and emission window 4 are formed with opposition, and a pair of the electrodes 5, 6 are located at the both sides by clipping the straight line tying the incident and emission window. Further, in the scintillation detector 7, the solidstate scintillator 9 of disc shape and the photo electron multiplier 10 are provided in the shield cylinder 8, the ray incident window of the multiplier 10 is adhered to one surface of the scintillator 9, and another surface of the scintillator 9 is opposed to the emission window 4 of the ionization chamber 1. The terminal 11 of one electrode 5 of the ionization chamber 1 is connected to the positive high voltage source 12, capacitor 13 and resistor 14 are connected in parallel with another electrode 6, the pulse from the parallel circuit is fed to the amplifying circuit 15 and the output pulse of the detector 7 is fed to the amplifying shape circuit 16, the output of the circuits 15, 16 is synthesized 17 and fed to the scaler.