| 摘要 |
PURPOSE:To enable drop of a voltage to the minimum even when a reverse bias leak current of a detector is large by a method wherein a current for compensation of a reverse-direction leak current is supplied to a current input terminal of a charge amplifier and an output voltage is inputted to a control circuit. CONSTITUTION:An output of a memory 9 controlled by a control circuit 8 is inputted to a voltage control constant-current circuit 11 through a D-A converter 10 and a constant current I is inputted therefrom to a current input terminal of a charge amplifier 2. Thereby a reverse-direction leak current is compensated. A current flowing through a feedback resistance Rf 4 of the amplifier 2 is made as small as possible. When a bias voltage is impressed on a radiation detector 1, it is increased by a very small amount by the circuit 8, the circuit 11 is adjusted at every time of the increase by the circuit 8 so that an output voltage of the amplifier 2 be within a prescribed range, and thereby the bias voltage of the detector 1 is stepped up to a final value.
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