Abstract: A radiation detector includes: a detector case which has an opening portion, a reflector which is attached to the opening portion of the detector case, a plastic scintillator which is disposed inside of the detector case, with a clearance from the reflector, a light guide into which fluorescence emitted from the plastic scintillator enters, a photo multiplier tube at which the fluorescence having passed through the light guide enters, and a pre amplifier which converts an output of the photo multiplier tube into a current pulse; wherein the plastic scintillator or the light guide has a soaked layer of ammonia which is formed on a surface thereof. This radiation detector is improved in the chemical resistance to the process fluid which includes a corrosive gas.

Abstract: A radiation detector includes: a detector case which has an opening portion, a reflector which is attached to the opening portion of the detector case, a plastic scintillator which is disposed inside of the detector case, with a clearance from the reflector, a light guide into which fluorescence emitted from the plastic scintillator enters, a photo multiplier tube at which the fluorescence having passed through the light guide enters, and a pre amplifier which converts an output of the photo multiplier tube into a current pulse; wherein the plastic scintillator or the light guide has a soaked layer of ammonia which is formed on a surface thereof. This radiation detector is improved in the chemical resistance to the process fluid which includes a corrosive gas.

Abstract: An in-core nuclear instrumentation apparatus is provided with a neutron flux current detection circuit which converts a neutron flux current signal fed from a neutron detector into a voltage signal and amplifies the voltage signal with a capability to continuously vary amplifier gain. The neutron flux current detection circuit includes a current sensing resistor for converting the neutron flux current signal into the voltage signal, an amplifier for amplifying the voltage signal, wherein an equivalent resistance value of a feedback circuit of the amplifier can be controllably varied, an equivalent resistance control circuit for varying the equivalent resistance value of the feedback circuit, and an output circuit which outputs an output terminal voltage signal of the amplifier.